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 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.

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.

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.

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.