Computational analysis of unsteady flow in turbine part of turbocharger

Abstract

Turbocharging technique is widely employed in internal combustion engines to improve the performance and to reduce the exhaust emissions. Flow analysis through the turbocharger has been a guiding method to optimize the turbocharger design. Usually, the turbocharger turbine is analyzed at steady states. But in practical scenario the turbine operates with unsteady flow due to the reciprocating motion of exhaust port and creates unsteady environment in the turbine. In order to increase turbine efficiencies and effective engine turbocharger matching, proper understanding of unsteady flow physics within the turbine is essential. Currently the turbine and compressors maps are obtained by using 1D code which includes extrapolation techniques. These methods neglect heat transfer and windage effects, hence resulting in lower aerodynamic efficiencies. Three dimensional analysis could lead to a better estimation of the flow field, helping the designer to build a high efficiency turbocharger. The present article concentrates on investigating unsteady flow field in the turbine part of a turbocharger. The necessary unsteady conditions at turbine inlet were obtained using commercially available one dimensional engine simulation software AVL Boost. A turbocharged twin cylinder CRDI diesel engine test rig was modelled within the workspace. The exhaust mass flow rate, pressure and temperature were recorded as a function of crank angle. These results were used as the boundary condition for the 3D analysis of the turbine. ANSYS CFX tools were used to solve the unsteady case. The turbine geometry was generated using ANSYS bladegen. The model selected for analysis is k-? turbulence Model. The pulsating performance, effect of secondary flows and entropy generation are discussed in the paper. © Springer India 2017.