Energy EngineerPh.D.

Global Fellowship

ROTRANS: Rotating Devices Performing Subsonic Supersonic Flow Transitions

WHY IS IT IMPORTANT...

Occurring shock systems in the supersonic flows, e.g. at the leading edge of the turbomachine rotor, reduce the machine efficiency drastically and threaten the responsible use of energy. The started project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. It is divided into an outgoing phase at Purdue University and a return phase at TU Berlin. During the outgoing phase, a numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. Back at the TU Berlin, the final applicability of the reduced model and the functionality of the novel concept will be assessed by a design optimization of a turbine and a compressor geometry.

What is it about...

RESEARCH SCOPE

Occurring shock systems in the supersonic flows, e.g. at the leading edge of the turbomachine rotor, reduce the machine efficiency drastically and threaten the responsible use of energy. The started project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. It is divided into an outgoing phase at Purdue University and a return phase at TU Berlin. During the outgoing phase, a numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. Back at the TU Berlin, the final applicability of the reduced model and the functionality of the novel concept will be assessed by a design optimization of a turbine and a compressor geometry.

HOW WE DO IT...

WORKPLAN

CFD SIMULATIONS
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REDUCED MODELING
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EXPERIMENTS
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OPTIMIZATION
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PROGRESS...

PROJECT RESULTS

Occurring shock systems in the supersonic flows, e.g. at the leading edge of the turbomachine rotor, reduce the machine efficiency drastically and threaten the responsible use of energy. The started project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. It is divided into an outgoing phase at Purdue University and a return phase at TU Berlin. During the outgoing phase, a numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. Back at the TU Berlin, the final applicability of the reduced model and the functionality of the novel concept will be assessed by a design optimization of a turbine and a compressor geometry.

ABOUT

Welcome to my website, where I share content related to my research on modeling, design, and analysis of compact turbines with both subsonic and supersonic flow.

SHORT BIO

ABOUT ME

Already at an early stage of my studies, I focused on complex aerothermodynamics of internal flows and turbomachinery, which quickly became my joy. In an internship and over the time of my Bachelor's thesis and Master's thesis I gained practical experience in the numerical simulation of compressor aerodynamics by means of CFD. At the end of 2013, I graduated with a Master's degree in turbomachinery and propulsion from the RWTH. During the period of my Ph.D. and an engagement as a postdoctoral researcher at the Universitat Politecnica de Valencia, Spain, I became an expert in radial turbine aerodynamics. Over the last years, I was able to profound my knowledge in CFD and was able to achieve advancements in the field of turbocharger turbine measurement methods and in the fields of one-dimensional modeling of radial turbine tip leakage flow and overall radial turbine performance. During an only four months lasting research stay at Purdue University, I was able to demonstrate the efficient use of my skills in a new working environment and on a different research topic. With the symbiotically matching know-how of the research group, the development of a novel kind of supersonic radial turbine and the registration of a provisional design patent was achieved in a very short time. With the acquired knowledge, I proposed a project together with TU Berlin and Purdue University to the European Commission and achieved the funding of our ROTRANS project as a Marie Curie Global Fellowship.

PASSION

INTERNATIONAL RESEARCHER

As a child, I could never imagine living abroad, although I always felt an inherent curiosity for different cultures. Then when I graduated from RWTH Aachen, I had the desire for continuous learning not only professionally but also in private, which pushed me towards the decision to do a Ph.D. abroad. A variety of reasons made me accept a position in Valencia, Spain. It was a professionally as well as personally truly enriching experience, even more than I could ever imagine before. Now, I see no other way than continuing on this path. Pushing for new technologies, while getting to know new places, languages, and people has become my passion. In the coming two years, I will be conducting research in the US. Following, I will move to Germany for one year to finish my Marie Curie Global Fellowship. Although this is my home country, it will be an international experience for me, after living for 8 years abroad. Definitely, I will be able to see the life in Germany from another perspective.

RESEARCH INTERESTS

TURBOMACHINERY AERODYNAMICS

Aerothermodynamic modeling of turbomachinery requires a combination of creativity, engineering know-how, and mathematical knowledge and it is a great way to take advantage of my skillset. It is exciting to see how complex phenomena can be modeled with simplified models. Indeed, first comes a deep understanding of the complex phenomena and understanding of leading dynamics. A very help tool can be carefully executed Computational Fluid Dynamics simulations. Also here I like to dig deeper and deeper into the data and to distinguish leading phenomena from less important phenomena. The understanding of the physics behind of main mechanisms makes the reduced modeling an easier task. For the design of new machines both reduced models and CFD may be used to achieve a design. For achieving fast design resutls, reduced models are of higher interest. Indeed testing your final design is very exciting as well and proves the real applicability of the machine as well as the developed design process.

RESEARCH

Rotating Devices Performing Subsonic Supersonic Flow Transitions

DESCRIPTION OF THE PROJECT

<img src=https://www.lukasinhestern.com/wp-content/uploads/2020/10/OneMinuteSlide2.png width=300 height=172 class=aligncenter size-full wp-image-174/> <p> Occurring shock systems in the supersonic flows, e.g. at the leading edge of the turbomachine rotor, reduce the machine efficiency drastically and threaten the responsible use of energy. The project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. It is divided into an outgoing phase at Purdue University and a return phase at TU Berlin. During the outgoing phase, a numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. Back at the TU Berlin, the final applicability of the reduced model and the functionality of the novel concept will be assessed by a design optimization of a turbine and a compressor geometry. To go to the project page click <a href=https://lukasinhestern.com/global-fellowship/ target=&quot _blank&quot > <b>here</b></a>.</p>

One-Dimensional Engine Modeling and Model Fitting for Steady and Transient Simulations

DESCRIPTION OF THE PROJECT

The reliability of an inhouse VGT turbocharger model was validated in multiple steady operating conditions from low engine loads up to high load and from low rotational speeds to high speeds. Also transient tipin operation was validated. The inhouse model was integrated into a commercial engine simulation tool. A engine fitting strategy had to be found to validate the turbocharger model performance independently. This was achieved for steady as well as transient conditions. In transient conditions, the controll of the suddenly changing VGT position is one of the main issues. However, with found control strategies the engine model was adjusted adequately and turbocharger model results were used for further analyis. The results could be prented at the <a href=https://doi.org/10.1115/GT2018-76470 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b>TURBO EXPO</b></a>.

CFD Analysis of Turbocharger Turbine Aerodynamics from Design to Off-Design with Low Mass Flow Rates

DESCRIPTION OF THE PROJECT

CFD simulation of a radial turbocharger turbine were executed and analyzed. The reduced mass flow map and turbine efficiency match the experimental results in high accuracy up to extreme off-design condition where the efficiency even reaches negative values. Those simulations were executed for three different VGT positions. The high validation quality indicates the reliability of the three-dimensional flow phenomena. It was observed that a dominant reverse flow can develop at the exit of the rotor at its hub. This flow phenomena can be observed at efficiencies around 40 percent when the outlet swirl is high. <a href=https://doi.org/10.1115/GT2017-63368 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b>These</b></a> and further numerical results gave the opportunity to analyze and to characterize tip leakage flow in radial turbines.

Advanced tip leakage modeling for radial turbines

DESCRIPTION OF THE PROJECT

Tip leakage losses are one of the main contributor to the overall losses encountered in small size radial turbocharger turbine. Flow passing the tip gap does experience much less extraction of total enthalpy and at the same time high-pressure losses. The related reduction in overall power extraction and the contribution to the pressure loss is directly related to the quantity of leakage. The tip leakage flow of a turbine depends mostly on the counterplay of friction driven and pressure-driven flow. This relation depends on a variety of factors as rotational speed, blade loading, incidence angle, and tip gap height. Hence, the tip leakage flow is highly dependent on the operating condition and thus, its adequate modeling gains significant importance in one-dimensional extrapolation models. In an extended effort, these complex flow relations have been characterized and all dependent parameters were characterized with a small number of coefficients. Several papers were published on this topic within this project. The <a href=https://doi.org/10.1016/j.energy.2018.01.083 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b> first paper</b></a> proposes a one-dimensional loss model to be integrated into a meanline extrapolation model and explains the equation derivation. A <a href=https://doi.org/10.1115/GT2018-76490 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b> second paper</b></a> tries to reach a generally valid form of tip flow characterization with different tip gap heights. The <a href=https://doi.org/10.1016/j.ijheatfluidflow.2019.108423 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b> third paper</b></a> evolves the method of tip flow characterization to a mature stage.

Meanline modeling for radial turbocharger turbine performance extrapolation

DESCRIPTION OF THE PROJECT

Due to the importance of etreme off-design conditions in radial turbocharger turbines and limited capability to meassure at those operting conditions in the industry, extrapolation models are required to extend narrow supplier maps. A extrapolation model based on reduced numbers and using the advanced tip leakage model developed in another project was developed. The experimental data obtained from several VGT positions can be used for one consistent fitting. The extrapolation model is suited for the extrapolation towards unknown expansion ratios, unknown VGT positions, and to unknown speeds. The available data from the experimental campaign allowed to validate the data in an uniquely available range of measurements.

Measurement of Extreme Off-Design Conditions with Low Pressure Ratio in Turbocharger Turbines

DESCRIPTION OF THE PROJECT

Increasingly tightening government restrictions on exhaust gas emissions put urban driving cycles more and more in the focus of engine designers. During these cycles the engine accelerates and decelerates causing highly unsteady operating condition for the turbocharger turbine. Hence, the performance of these conditions needs to be known and industrially applicable turbine testing at extreme off-design condistions are a need. In <a href=https://doi.org/10.1016/j.energy.2017.02.118 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b>this project</b></a>, a new method for the measurement of these critical operating conditions was outlined. As the measurement at low mass flow rates is highly sensitive to changes in heat transfer, the turbocharger geometry was maintained conserving the heat transfer characterization of the unit. In a <a href=https://doi.org/10.1115/GT2017-63360 target=&quot _blank&quot rel= &quot noopener noreferrer&quot > <b>second step</b></a>, the developed technique was industrialized to allow manufacturers to test every unit in a suited testbench.

PUBLICATIONS

01 Jan 2024

Flow irreversibility and heat transfer effects on turbine efficiency

Applied Energy


Journal Paper Selected Lukas Benjamin Inhestern, Dieter Peitsch, Guillermo Paniagua

Flow irreversibility and heat transfer effects on turbine efficiency

Lukas Benjamin Inhestern, Dieter Peitsch, Guillermo Paniagua
Journal Paper Selected
About The Publication

The quantification of the flow irreversibilities is crucial to developing future turbomachinery. Traditionally, design correlations and efficiencies are based on comparisons to isentropic relations to quantify the deviation from an “ideal” case. However, isentropic relations typically assume one-dimensional adiabatic flow, representing a significant departure from the actual situation in turbines operating with large levels of heat transfer. In this paper, the aerothermal losses and power generation in reversible processes are derived for three-dimensional compressible flow considering heat transfer effects. A new definition of the power potential in a reversible process is proposed that can be used to perform detailed budgeting of the losses. The proposed new loss framework can be adopted locally, which enables the precise identification of the loss source. New aerodynamic and aerothermal efficiency expressions are proposed to assess shaft power extraction in combination with heat exchange. The new method enables designers to identify the regions with high loss generation in steady and also in unsteady flow conditions, offering new avenues to evaluate the loss generation mechanisms during the design phase. Therefore, our new tool is essential to developing reduced-order models for the design of future fluid machinery.

30 May 2023

Reduced-order-modeling of the transient starting in supersonic passages

Aerospace Science and Technology


Journal Paper Selected Lukas Benjamin Inhestern, Dieter Peitsch, Guillermo Paniagua

Reduced-order-modeling of the transient starting in supersonic passages

Lukas Benjamin Inhestern, Dieter Peitsch, Guillermo Paniagua
Journal Paper Selected
About The Publication

Characterizing the time scales of starting in supersonic passages is essential for future aerospace propulsion systems, such as supersonic intakes, Rotating Detonation Engines, and power generation systems based on Organic Rankine Cycles. This paper first compares 2D URANS results with 1D Euler results to identify the equations that govern the acceleration and deceleration of the strong shock during the starting process’s time evolution. Secondly, we characterized the effect of the frequency of pulsating flows on the starting process; intermediate frequencies around 1 kHz show best startability while higher and much lower frequencies can cause unstarting. Finally, using the governing terms for the shock acceleration and deceleration in the momentum transport equation, a reduced-order model was developed and coupled with an optimization algorithm to enable rapid designs with improved flow starting capability. An optimized design demonstrated dominant startability using URANS simulations in comparison to two other geometries. The developed method represents an essential tool for reduced time-to-market solutions for aerospace propulsion components, such as inlets, supersonic turbomachinery, and nozzles.

29 Mar 2019

Measurement, Simulation, and 1D-Modeling of Turbocharger Radial Turbines at Design and Extreme Off-Design Conditions

Universitat Politècnica de València

The thesis presents novel measurement methods for the evaluation of radial turbine off-design maps, new reduced tip leakage models with a high level of detail, and various well-validated CFD analyses unveiling unknown flow patterns at these operating conditions.

Thesis Selected Lukas Benjamin Inhestern

Measurement, Simulation, and 1D-Modeling of Turbocharger Radial Turbines at Design and Extreme Off-Design Conditions

Lukas Benjamin Inhestern
Thesis Selected
About The Publication
To achieve an optimal matching between the turbocharger and internal combustion engine over a wide range of the engine operation map, their complex interaction is commonly analyzed by means of transient one-dimensional modeling. The pulsating flow of the engine exhaust gases causes high variations of turbine inlet mass flow, total pressure, and total temperature. This pushes the turbocharger turbine operation towards extreme off-design conditions. Hence, wide turbine operation maps are required as input for the one-dimensional models. The measurement of turbine maps is typically restricted by compressor choke and surge. At the same time, only minor geometrical changes are required to maintain the important thermal characteristics of the turbocharger. In this thesis the turbocharger compressor was converted into a centrifugal turbine to assist the axis rotation when the turbine produces or even consumes low power. For enhancing the power output from the compressor wheel, an IGV was placed upstream of the compressor inlet. To reduce the effort for adiabatizing, a simple correlation only dependent on fluid temperature measurements was developed. Further test monitoring strategies were documented that can assist the measurement of off-design conditions. With the obtained off-design data a CFD setup for the achievement of convergent results in extreme off-design conditions was validated. To reduce the problem of high swirl angles in the turbine outlet when operating with low mass flows, the outlet duct was extended and a tapered duct had to be attached just before the domain outlet. By means of the well validated CFD results, three-dimensional flow effects were analyzed. Operating in high off-design conditions the outlet swirl and thus, the static pressure gradient was so high that the flow collapses and a reverse flow develops. This reverse flow reenters the rotor and mixes again with the main flow. On one hand this effect produces pressure losses and locally negative torque at the hub. However, on the other hand the reentering flow increases the mass flow locally and restricts the flow section close to the hub. Hence, blade loading and local torque production are increased close to the shroud. Although a clear change in the stage loading vs. flow coefficient plot was noticed as soon as the reverse flow occurs, no clear impact on the efficiency can be seen. Further analysis of tip leakage flow over a wide range showed the importance of friction driven flow and incidence induced leakage flow in off-design condition. In general, greater tip leakage losses were observed as further the turbine operates away from the design point. Furthermore, it was stated that a commonly used correlation for the characterization of tip leakage flow is not capable of reproducing either qualitative trends nor quantities when the tip gap height or the operating point is varied. Finally, the observed effects were modeled in one-dimensional form. A tip leakage loss model that is capable of reproducing the found trends and shows good extrapolation capability was developed. Results were validated using three-dimensional CFD data. As a result, it was possible to develop a novel method for tip leakage flow characterization, which can model tip leakage flow momentum and velocities for varying tip gap heights in design and off-design conditions. Following, a complete one-dimensional extrapolation model for adiabatic turbine efficiency maps was developed. Taking advantage of the newly developed tip leakage model and other findings from the CFD campaign, good extrapolation quality in terms of speed, blade-to-jet speed ratio and VGT opening was achieved. High accuracy of the results was stated by the comparison with the initially measured wide range data.
07 May 2020

Design and Numerical Analysis of Flow Characteristics in a Scaled Volute and Vaned Nozzle of Radial Turbocharger Turbines

Energies

This paper represents an interesting analysis of the Reynolds and Mach similitude applied on the volute and stator vane passage in a radial turbine. The geometry of an originally sized and upscaled radial turbine has been analyzed and compared.

Journal Paper Selected Andrés Omar Tiseira Izaguirre, Roberto Navarro García, Lukas Benjamin Inhestern, Natalia Hervás Gómez

Design and Numerical Analysis of Flow Characteristics in a Scaled Volute and Vaned Nozzle of Radial Turbocharger Turbines

Andrés Omar Tiseira Izaguirre, Roberto Navarro García, Lukas Benjamin Inhestern, Natalia Hervás Gómez
Journal Paper Selected
About The Publication

Over the past few decades, the aerodynamic improvements of turbocharger turbines contributed significantly to the overall efficiency augmentation and the advancements in the downsizing of internal combustion engines. Due to the compact size of automotive turbochargers, the experimental measurement of the complex internal aerodynamics has been insufficiently studied. Hence, turbine designs mostly rely on the results of numerical simulations and the validation of zero-dimensional parameters as efficiency and reduced mass flow. To push the aerodynamic development even further, a precise validation of three-dimensional flow patterns predicted by applied computational fluid dynamics (CFD) methods is in need. This paper presents the design of an up-scaled volute-stator model, which allows optical experimental measurement techniques. In a preliminary step, numerical results indicate that the enlarged geometry will be representative of the flow patterns and characteristic non-dimensional numbers at defined flow sections of the real size turbine. Limitations due to rotor-stator interactions are highlighted. Measurement sections of interest for available measurement techniques are predefined.

10 Feb 2020

Design, Optimization, and Analysis of Supersonic Radial Turbines

Journal of Engineering for Gas Turbines and Power

This paper describes the design optimization of a novel type of radial supersonic turbine. The design can be coupled with any kind of detonation combustor with axial outflow and even subsonic inflow can be utilized for efficient power harvesting. The final design has been filed as a patent.

Journal Paper Selected Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua, José Ramón Serrano Cruz

Design, Optimization, and Analysis of Supersonic Radial Turbines

Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua, José Ramón Serrano Cruz
Journal Paper Selected
About The Publication
New compact engine architectures such as pressure gain combustion require ad hoc turbomachinery to ensure an adequate range of operation with high performance. A critical factor for supersonic turbines is to ensure the starting of the flow passages, which limits the flow turning and airfoil thickness. Radial outflow turbines inherently increase the cross section along the flow path, which holds great potential for high turning of supersonic flow with a low stage number and guarantees a compact design. First, the preliminary design space is described. Afterward a differential evolution multi-objective optimization with 12 geometrical design parameters is deducted. With the design tool autoblade 10.1, 768 geometries were generated and hub, shroud, and blade camber line were designed by means of Bezier curves. Outlet radius, passage height, and axial location of the outlet were design variables as well. Structured meshes with around 3.7 × 106 cells per passage were generated. Steady three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) simulations, enclosed by the k-omega shear stress transport turbulence model were solved by the commercial solver CFD++. The geometry was optimized toward low entropy and high-power output. To prove the functionality of the new turbine concept and optimization, a full wheel unsteady RANS simulation of the optimized geometry exposed to a nozzled rotating detonation combustor (RDC) has been performed and the advantageous flow patterns of the optimization were also observed during transient operation.
03 Dec 2019

Radial turbine sound and noise characterisation with acoustic transfer matrices by means of fast one-dimensional models

International Journal of Engine Research

This article presents a method for generating lookup tables for acoustic transfer matrices by means of fast one-dimensional simulations of thoroughly validated fidelity, in terms of both acoustics and extrapolation capabilities. The presented method allows to reduce the computational cost of one-dimensional turbine acoustic simulations.

Journal Paper Antonio Torregrosa, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Pablo Soler

Radial turbine sound and noise characterisation with acoustic transfer matrices by means of fast one-dimensional models

Antonio Torregrosa, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Pablo Soler
Journal Paper
About The Publication
Estimating correctly the turbine acoustics can be valuable during the engine design stage; in fact, it can lead to a more optimised design of the silencer and aftertreatment, as well as to better prediction of the scavenging effects. However, obtaining the sound and noise emissions of radial turbocharger turbines with low computational costs can be challenging. To consider these effects in a time-efficient manner, the acoustic response of single-entry radial turbines can be characterised by means of acoustic transfer matrices that change with the operating conditions. Exploiting the different time-scales of the acoustic phenomena and the change in the operating point of the turbine, lookup tables of acoustic transfer matrices can be computed. Then, the obtained characterisation can be used in mean-value engine models. This article presents a method for generating these lookup tables by means of fast one-dimensional simulations of thoroughly validated fidelity, in terms of both acoustics and extrapolation capabilities. Due to the inherent behaviour of radial turbines, the number of computations needed to fill the lookup tables is relatively small, so the method can be used as a simple preprocessing phase before mean-value simulation campaigns.
30 Jun 2019

Design, Optimization and Analysis of Supersonic Radial Turbines

ASME Turbo Expo 2019 in Phoenix, Arizona

This conference paper describes the design optimization of a novel type of radial supersonic turbine. The design can be coupled with any kind of detonation combustor with axial outflow and even subsonic inflow can be utilized for efficient power harvesting. The final design has been filed as a patent.

Conference Paper Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua, José Ramón Serrano Cruz

Design, Optimization and Analysis of Supersonic Radial Turbines

Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua, José Ramón Serrano Cruz
Conference Paper
About The Publication
New compact engine architectures such as pressure gain combustion require ad-hoc turbomachinery to ensure an adequate range of operation with high performance. A critical factor for supersonic turbines is to ensure the starting of the flow passages, which limits the flow turning and airfoil thickness. Radial outflow turbines inherently increase the cross section along the flow path, which holds great potential for high turning of supersonic flow with a low stage number and guarantees a compact design. First, the preliminary design space is described. Afterwards, a differential evolution multi-objective optimization with 12 geometrical design parameters is deducted. With the design tool AutoBlade 10.1, 768 geometries were generated and hub, shroud, and blade camber line were designed by means of Bezier curves. Outlet radius, passage height, and axial location of the outlet were design variables as well. Structured meshes with around 3.7 million cells per passage were generated. Steady three dimensional Reynolds averaged Navier Stokes (RANS) simulations, enclosed by the k-omega SST turbulence model were solved by the commercial solver CFD++. The geometry was optimized towards low entropy and high power output. To prove the functionality of the new turbine concept and optimization, a full wheel unsteady RANS simulation of the optimized geometry exposed to a nozzled rotating detonation combustor (RDC) has been performed and the advantageous flow patterns of the optimization were also observed during transient operation.
05 Nov 2019

Unsteady Heat Transfer Assessment of Supersonic Turbines Downstream of a Rotating Detonation Combustor

ASME Turbo Expo 2019 in Phoenix, Arizona

A radial supersonic turbine and an axial supersonic turbine were numerically exposed to the outflow of a rotating detonation combustor. Isothermal simulations allowed the evaluation and comparison of heat transfer phenomena in these novel types of turbines.

Conference Paper Zhe Liu, Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua

Unsteady Heat Transfer Assessment of Supersonic Turbines Downstream of a Rotating Detonation Combustor

Zhe Liu, Lukas Benjamin Inhestern, James Braun, Guillermo Paniagua
Conference Paper
About The Publication
The supersonic outlet conditions from a rotating detonation combustor exhibit fluctuations in temperature and pressure that exceed 200% of their mean level. Such unsteady conditions will induce a large convective heat loading onto a downstream supersonic turbine. Hence, the precise evaluation of the thermal load to the vane and rotor is essential to the design of adequate cooling strategies. In this paper, a numerical framework is proposed to compute the convective heat transfer on two types of supersonic turbines: axial and radial outflow. The fluctuations imposed at the turbine inlet were obtained from a nozzle coupled to a rotating detonation combustor. Both radial and axial turbines were designed and subsequently analyzed with full stage unsteady simulations using an Unsteady Reynolds Averaged Navier–Stokes solver. The inlet boundary conditions to the turbine are based on CFD results from a rotating detonation combustor. The unsteady adiabatic convective heat transfer coefficient was obtained from two simulations performed at a fixed homogeneous wall temperature. The heat flux variation in span-wise and stream-wise direction is analyzed in detail. Budgeting of the unsteady heat flux mechanism was performed to identify the driving contributor of the heat transfer within the turbine and finally both designs are compared.
01 Aug 2019

An innovative losses model for efficiency map fitting of vaneless and variable vaned radial turbines extrapolating towards extreme off-design conditions

Energy

A novel extrapolation model, which can be fitted with the data of different VGT positions at the same time is explained. The results have been validated with numerous experimental data. Novel tip leakage models were used. Only reduced input numbers can be used.

Journal Paper Selected José Ramón Serrano, Francisco José Arnau, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern

An innovative losses model for efficiency map fitting of vaneless and variable vaned radial turbines extrapolating towards extreme off-design conditions

José Ramón Serrano, Francisco José Arnau, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern
Journal Paper Selected
About The Publication
Pulsating flow in automotive turbocharger turbines makes it necessary to know performance characteristics in difficult to measure off-design conditions. Physically-based extrapolation models can be used to extrapolate towards unmeasured map regions. However, for model parameter fittings common maps have low numbers of measurement points per speedline available. Measurements with different variable geometry turbine (VGT) openings amplify the available data and help to characterize the turbine in a wider aerodynamic range. Nevertheless, physical models able to fit the data of several speeds and VGT positions with the same set of fitting parameters are rare. Thus, a model that is capable of fitting all speeds and VGT positions simultaneously and with the capability of extrapolating reliably towards low pressure ratios, unmeasured speeds, and VGT openings has been developed. The model is based on novel and commonly used loss correlations combined in an innovative way and have been validated in a wide range of pressure ratios towards extreme off-design conditions. By deactivating stator passage effects, the model can also extrapolate efficiency maps of vaneless turbines. The set of loss models is able to reproduce the measured data in good quality for tested turbines with a very reduced number of fitting coefficients.
01 Aug 2019

Contribution to tip leakage loss modeling in radial turbines based on 3D flow analysis and 1D characterization

International Journal of Heat and Fluid Flow

Tip leakage flow is characterized in a new manner. It was shown that the tip leakage flow of a wide range of operating points including extreme off-design points and with varying tip gap heights can be characterized with only three parameters. Found coefficients with one geometry are valid for changed tip gap geometries.

Journal Paper Selected José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern

Contribution to tip leakage loss modeling in radial turbines based on 3D flow analysis and 1D characterization

José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern
Journal Paper Selected
About The Publication

The characterization of tip leakage flow plays an important role for one-dimesional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional tip leakage momentum ratio, a novel correlation has been derived. This allows a consistent characterization for variable tip gap sizes over a wide range of operating conditions. The correlation has been validated by means of CFD data with high variety in reduced speed tip gap geometry and expansion ratios. Results of the novel number show significant improvements of quantitative and qualitative results over a wide range of running conditions in comparison to existing correlations. Furthermore, correlations for tip leakage velocities, that can easily be used in one-dimensional models, have been derived. Finally, it has been demonstrated, that the influence of inlet flow momentum on the tip leakage flow can be analyzed with presented correlations.

30 May 2018

Method for Non-Dimensional Tip Leakage Flow Characterization in Radial Turbines

ASME Turbo Expo 2018 in Oslo, Norway

The friction driven and pressure-driven flow has been quantified by means of CFD results. A relation of tip clearance specific Reynolds numbers has been found to represent an adequate number for the consistent characterization of tip leakage flow.

Conference Paper José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern

Method for Non-Dimensional Tip Leakage Flow Characterization in Radial Turbines

José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern
Conference Paper
About The Publication

Tip leakage loss characterization and modeling plays an important role in small size radial turbine research. The momentum of the flow passing through the tip gap is highly related with the tip leakage losses. The ratio of fluid momentum driven by the pressure gradient between suction side and pressure side and the fluid momentum caused by the shroud friction has been widely used to analyze and to compare different sized tip clearances. However, the commonly used number for building this momentum ratio lacks some variables, as the blade tip geometry data and the viscosity of the used fluid. To allow the comparison between different sized turbocharger turbine tip gaps, work has been put into finding a consistent characterization of radial tip clearance flow. Therefore, a non-dimensional number has been derived from the Navier Stokes Equation. This number can be calculated like the original ratio over the chord length. Using the results of a wide range of CFD data, the novel tip leakage number has been compared with the traditional and widely used ratio. Furthermore, the novel tip leakage number can be separated into three different non-dimensional factors. First, a factor dependent on the radial dimensions of the tip gap has been found. Second, a factor defined by the viscosity, the blade loading, and the tip width has been identified. Finally, a factor that defines the coupling between both flow phenomena. These factors can further be used to filter the tip gap flow, obtained by CFD, with the influence of friction driven and pressure driven momentum flow.

30 May 2018

Analysis of Unsteady Energy Fluxes in a Turbocharger by Using a Holistic Model Extrapolating Standard Lookup Tables in Full Engine Operating Map

ASME Turbo Expo 2018 in Oslo, Norway

Energy fluxes were assessed over the entire operating range of a Diesel engine. The isentropic transient turbine power and its use was analyzed in detail and also over the entire operating range. Map regions of high energy losses were identified and confirmed.

Conference Paper José Ramón Serrano, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Stephane Guilain, Hadi Tartoussi

Analysis of Unsteady Energy Fluxes in a Turbocharger by Using a Holistic Model Extrapolating Standard Lookup Tables in Full Engine Operating Map

José Ramón Serrano, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Stephane Guilain, Hadi Tartoussi
Conference Paper
About The Publication

One dimensional modeling can give important insights into the needs of engine and turbocharger design. In this paper a holistic turbocharger model that calculates besides transient effects also heat transfer, friction losses, extrapolated adiabatic turbine and compressor maps has been validated over the range of an entire diesel engine map. Due to its capability of calculating heat fluxes in very different conditions turbocharger maps measured in hot as well as maps measured in cold conditions can be used as input data of the model. The turbocharger model has been validated in a high number of running conditions and has been compared against a reference model to highlight its advantages. Since the model can calculate data that are difficult to measure as complex internal turbocharger heat transfer, entropy, and adiabatic efficiency pulses, these numbers have been analyzed. It has been found out that the analyzed turbocharger loses relatively high amounts of heat especially at its highest efficiency zone. Further, the importance of the isentropic power during the valley in engine exhaust gas flow pulses has been highlighted. Apart from the peak energy a big part of isentropic energy is available in the valley of the pulse. Finally, a specific coefficient has been proposed to quantify the available energy rate in the valley of the pulse.

15 Mar 2018

Turbocharger turbine rotor tip leakage loss and mass flow model valid up to extreme off-design conditions with high blade to jet speed ratio

Energy

Derived from the Navier Stokes equations for flow in a cylindric thin passage a tip leakage loss model was derived. In comparison with validated CFD data the model shows extraordinary extrapolation ability when only a few data are given at design condition.

Journal Paper José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern

Turbocharger turbine rotor tip leakage loss and mass flow model valid up to extreme off-design conditions with high blade to jet speed ratio

José Ramón Serrano, Roberto Navarro, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern
Journal Paper
About The Publication

Due to the power consumption restriction of the turbocharger compressor, common turbine maps are rather narrow. To extrapolate them, reliable physical submodels are needed that are valid for broad ranges. Plenty of research has been done referring to tip leakage losses in axial and traditional radial turbomachinery. However, less effort has been put into the tip leakage analysis of radial turbocharger turbines, whose characteristics including high rotational speed and geometry are rather different. Commonly developed tip leakage loss models in radial turbines are mainly based on correlations with the rotational speed, while in axial turbomachinery they are mainly based on blade loading assumptions. Wide range computational fluid dynamics (CFD) data of a medium sized automotive turbine have been used to analyze tip leakage mass flow under extremely diverse running conditions. To be able to fit a model in a broad range of the map, blade loading and rotational speed have to be considered. A novel tip clearance model has been derived from the Navier Stokes Equations. The model owns a dependency on the rotational speed and the blade loading. With this approach CFD data have been fitted in a very good quality to model the tip leakage mass flow rate and tip leakage losses.

30 Jun 2017

Extremely Low Mass Flow at High Blade to Jet Speed Ratio in Variable Geometry Radial Turbines and its Influence on the Flow Pattern: A CFD Analysis

ASME Turbo Expo 2017 in Charlotte, North Carolina

The numerical setup used in other papers was described in this paper. A detailed mesh analysis is presented. At extreme off-design condition with low mass flow, a recirculation region was identified in the outlet of the turbine rotor. This recirculation has its origin at the hud and grows continuously with decreasing overall mass flow.

Conference Paper José Ramón Serrano, Antonio Gil, Roberto Navarro, Lukas Benjamin Inhestern

Extremely Low Mass Flow at High Blade to Jet Speed Ratio in Variable Geometry Radial Turbines and its Influence on the Flow Pattern: A CFD Analysis

José Ramón Serrano, Antonio Gil, Roberto Navarro, Lukas Benjamin Inhestern
Conference Paper
About The Publication

In urban driving the turbocharger turbine faces high changes due to frequent acceleration and deceleration so that extremely low mass flow can occur. However, the flow behavior in turbocharger turbines at these extreme off-design conditions is rather unknown. So the development of physically-based models for extrapolating the usually narrow experimental turbine maps and advanced measurements to increase the range of turbine maps has been in the focus of many researchers. To provide valuable information about those flow characteristics, this paper supplies a detailed analysis at low mass flow in a radial turbocharger turbine. The turbine has been experimentally characterized under steady flow from normal operating working conditions up to extreme off-design points, where the turbine could even work with negative efficiency. Since heat transfer significantly affects the turbine efficiency calculation when turbine power is low, the experiments have been executed under quasi-adiabatic conditions and residual heat fluxes have further been corrected. This paper takes advantage of these data to validate adiabatic CFD simulations in a wide operating range, from optimum efficiency point up to negative turbine power. Stationary and transient three-dimensional CFD simulations of the turbocharger turbine have been performed. The numerical campaign covers a wide range of operating conditions, providing different flow patterns. The obtained results show that the secondary flow field changes appreciably with mass flow rate. At low mass flows, a further backflow region develops over the entire circumference close to the hub, significantly constricting the effective turbine area and provoking mass flow instability. The highlighted flow phenomena will allow to improve state of the art extrapolation models and might help designers to understand turbine flow operating under extreme off-design conditions.

30 May 2017

Methodology to Evaluate Turbocharger Turbine Performance at High Blade to Jet Speed Ratio Under Quasi Adiabatic Conditions

ASME Turbo Expo 2017 in Charlotte, North Carolina

An experimental methodology to measure turbocharger turbines at low mass flow rates was improved and the industrialization of this previously introduced technique was achieved. Additionally, a heat transfer model that can be applied to quasi-adiabatic tests was developed.

Conference Paper José Ramón Serrano, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Holger Mai, Andrea Rinaldi, Adrian Miguel-Sanchez

Methodology to Evaluate Turbocharger Turbine Performance at High Blade to Jet Speed Ratio Under Quasi Adiabatic Conditions

José Ramón Serrano, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Holger Mai, Andrea Rinaldi, Adrian Miguel-Sanchez
Conference Paper
About The Publication

While turbocharging already combines high specific rated engine power with low fuel consumption, there is still potential for optimization to achieve prospective demands for fuel efficiency with low emissions. Using engine exhaust energy, the turbine underlies pulsating flow conditions from high towards zero mass flow at almost constant blade speed. The average turbine efficiency is then affected for the high blade to jet speed ratio conditions, which is very important at low engine loads during urban driving conditions. Since turbocharger performance is very sensitive for the overall engine efficiency, a very accurate measurement of the characteristic maps is desired to evaluate the thermodynamic behavior of the turbocharger and to ensure best possible matching. This paper presents a methodology to extend the turbine performance at low expansion ratio and to characterize the adiabatic efficiency in a wide operating range. This enables measuring turbines on a hot-gas test bench at very high blade to jet speed ratio and very low turbine flow to develop, improve, and validate reliable turbocharger models that can be used for full engine simulations. The industrial applicability has been proven from very low turbine power up to negative turbine power output simply based on using inlet guide vanes (IGV) upstream of the compressor. By generating a swirl in the compressor wheel rotating direction and pressurizing the inlet air, the compressor can be run as a turbine. Thus, the compressor provides power to the shaft and the turbine can be driven with very low flow power. The test campaign has been realized under quasi-adiabatic conditions to limit the heat transfer. While measuring at three different oil temperatures, the impact of remaining internal heat transfer has been taken into account. A turbocharger heat transfer model has also been used to correct residual heat flows from the obtained data set for all oil temperatures.

15 Apr 2017

Radial turbine performance measurement under extreme off-design conditions

Energy

An experimental method to measure turbocharger turbine performance at very low mass flow rates has been introduced. The method allows measurements without modifications of the turbocharger unit which is of high importance to maintain the thermal characterization of the unit. Achieved data were used for the validation of CFD models and one-dimensional models of other papers.

Journal Paper Selected José Ramón Serrano, Andrés Tiseira, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Hadi Tartoussi

Radial turbine performance measurement under extreme off-design conditions

José Ramón Serrano, Andrés Tiseira, Luis Miguel García-Cuevas, Lukas Benjamin Inhestern, Hadi Tartoussi
Journal Paper Selected
About The Publication

During automotive urban driving conditions and future homologation cycles, automotive radial turbines experience transient conditions, whereby the same operate at very high blade speed ratios and, thus, at very low power outputs. Under those conditions, the turbine power output might not be enough to feed the mechanical power needs of the compressor. Typical fast one-dimensional full engine simulations rely on steady-state performance maps to characterize the turbocharger. Due to the restricting compressor braking power, extreme off-design measurements cannot be obtained in standard gas stands without using an external brake instead of the compressor or without using a motor attached to the turbocharger shaft. Such turbocharger assemblies cause shaft balancing issues inherent to the connection to a brake operating at high rotational speeds or need basic changes of the turbocharger geometry. This paper presents a novel approach for turbine performance map measurements at very low expansion ratio and very low mass flow without the aforementioned issues. The method uses the turbocharger compressor as a centrifugal turbine, providing mechanical power to the shaft and enabling turbine performance measurements from points of very high expansion ratio up to very low pressure ratio. It is even possible to measure at almost zero flow rate in the turbine when it consumes shaft power instead of producing it. This experimental procedure that can be applied to whatever turbocharger produces valuable information for the development and validation of turbine performance models aiming to extrapolate its behaviour at off-design conditions.

RESUME

ACADEMIC AND PROFESSIONAL POSITIONS
  • Present
    2020
    BERLIN, GERMANY

    Marie Curie Research Fellow

    TECHNICAL UNIVERSITY BERLIN

    Occurring shock systems in the supersonic flows, e.g. at the leading edge of the turbomachine rotor, reduce the machine efficiency drastically and threaten the responsible use of energy. The started project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. It is divided into an outgoing phase at Purdue University and a return phase at TU Berlin. During the outgoing phase, a numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. Back at the TU Berlin, the final applicability of the reduced model and the functionality of the novel concept will be assessed by a design optimization of a turbine and a compressor geometry.
  • Present
    2020
    WEST LAFAYETTE, UNITED STATES

    VISITING RESEARCHER

    PURDUE UNIVERSITY

    During the outgoing phase of the Marie Curie Global Fellowship, the project aims at developing a new understanding of the shock establishment and high-frequency response within the rotor. A numerical analysis of the observed phenomenon will be conducted to develop a reduced model based on 3D characteristics. This model will thoroughly be validated by advanced experimental measurements. The aim is to transfer a fully validated model, which can be used for the design of transonic turbines and compressors.
  • 2020
    2019
    VALENCIA, SPAIN

    POSTDOCTORAL RESEARCH ASSISTANT

    Universitat Politècnica de València (UPV)

    One-dimensional simulations of an entire internal combustion engine and validation of integrated inhouse coded turbocharger compound considering a novel extrapolation model (developed during PhD thesis) were performed. Further, CFD simulations of turbocharger turbines at choked conditions were performed and supervised. Studies of scaled turbocharger geometries considering similitude analysis were supervised and CFD simulations were launched. Finally, turbocharger acoustics were numerically assessed at pulsating and steady flow conditions.
  • 2018
    2018
    WEST LAFAYETTE, UNITED STATES

    Visiting Scholar

    PURDUE UNIVERSITY

    Development of a novel concept of supersonic radial turbines with axial inflow. The design was optimized by means of a multiobjective optimizer. The heat transfer and aerodynamic performance of the final design exposed to the outflow of a rotating detonation combustor were numerically assessed. A provisional design patent has been filed.
  • 2013
    2013
    COLOGNE, GERMANY

    Graduate Student Assistant

    German Aerospace Center (DLR)

    A Study on the meshing and simulation of semi-clearances of variable stator vanes was performed. Occurring divergence problems related to meshing strategies were successfully analyzed. Effective advice for the meshing of semi-clearances and tip clearances could be given to enhance the numerical stability of the simulations.
  • 2013
    2012
    AACHEN, GERMANY

    Bachelor's Student

    RWTH Aachen University

    The numerical validation of a radial compressor and compressor map calculation of a mixed flow compressor was conducted. The validation of a publicly available test case, which was frequently used in the literature led to the conclusion that an important pressure loss was previously neglected. The neglect was cause of rather big differences between test case and simulation results. Further, the aerodynamics of a mixed flow compressor were analyzed and compared to common radial compressor aerodynamics.
EDUCATION
  • 2019
    2014
    VALENCIA, SPAIN

    Doctor of Philosophy (PhD)

    Universitat Politècnica de València (UPV)

    The pulsating flow of the engine exhaust gases causes high variations of turbine inlet mass flow, total pressure, and total temperature. This pushes the turbocharger turbine operation towards extreme off-design conditions. My thesis supplies new insights into the three-dimensional flow field under these conditions as well as a novel one-dimensional extrapolation model and new loss sub-models. Additionally, an experimental procedure for this hardly measurable conditions was developed.
  • 2016
    2014
    VALENCIA, SPAIN

    Master's degree in Reciprocating Internal Combustion Engines

    Universitat Politècnica de València (UPV)

    The master program is oriented to give profound insights into the entire system and a complete energetic understanding of internal combustion engines.
  • 2013
    2013
    AACHEN, GERMANY

    Master of Science (M.Sc.) in Energy Engineering

    RWTH Aachen University

    Studies were mainly focused on turbomachinery and jet propulsion. Courses treated aerodynamics, thermodynamics and technical combustion, and further topics around general energy engineering.
  • 2013
    2008
    AACHEN, GERMANY

    Bachelor's degree in Mechanical Engineering

    RWTH Aachen University

    At this prestigious engineering school, the theoretical fundamentals of a broad range of engineering disciplines are taught.
HONORS AND AWARDS
  • 2020
    BRUSSELS, BELGIUM

    Marie Curie Global Fellowship (H2020-MSCA-IF-2019)

    EUROPEAN COMMISSION

  • 2018
    VALENCIA, SPAIN

    TRAVEL GRANT

    UNIVERSITAT POLITÈCNICA DE VALÈNCIA (UPV)

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