Single entry mixed flow turbine performance prediction with 1-d gas dynamic code coupled with mean line model

It is a well known fact that turbocharger works with pulsating exhaust flow in its entire operating life, hence the need to predict unsteady performance. This paper presents the unsteady performance prediction resultof a single entry nozzleless mixed flow turbine under steady flow and 60 Hz pulsating flow at 43.0 rps/ √ K operating speed. The modeling method coupled one-dimensional gas dynamic modelwith a mean-line model to predict the turbine efficiency by appropriate losses consideration. The coupled method assumes that the turbine volute has a large volume and length, so that unsteadiness effect of the pulsating flow is significant while the rotor is assumed to behave quasisteadily. A pressure drop boundary is used to simulate pressure drop across the turbine volute. The coupled method was validated with the experimentally measured steady state results of the same turbine. Experimentally measured total conditions of the flow were used as inlet conditions for the model during unsteady analysis. The predicted isentropic power averaged results show convincing match with the experimental data. This will set forward a systematic approach for engine designers to evaluate turbine performance beyond what will be normally provided by turbocharger manufacturers, which is the steady state map. Keyword: Turbine, performance prediction, onedimensional gas dynamic model, mean-line model, losses INTRODUCTION Turbocharging technology is believed to play a crucial role in the engine downsizing development towards reducing green house emissions. In a case study conducted by Drescher [1], it was found that engine downsizing may contribute up to approximately 24% of the overall achievable fuel efficiency optimization. Due to the lower cost increment per unit CO2 reduction, internal combustion engine is forecasted to be the main powertrain source at least for the following two decades [2]. Computational turbine modeling is a powerful analysis tool yet much cheaper option in conjunction with the development of turbocharging technology, such as in the engine-turbocharger matching and optimizing exhaust system. In this paper, a precise modeling method for unsteady turbine performance prediction, which subsequently able to be used in engine model will be presented.