Study on a new pressure loss model of T-junction for compressible flow with particle image velocimetry test

Abstract

The energy transfer and conversion of exhaust gas flowing across junctions of exhaust manifold plays an important role in determining performance of turbocharging system. With the increase of engine boost pressure, exhaust gas velocity increases significantly, which increased compressibility of exhaust gas flow simultaneously. The existed exhaust T-junction models that do not take gas compressibility into consideration are not capable to simulate the exhaust gas flow with high boost pressure good enough. In order to predict pressure loss coefficients of high-pressure gas flow with higher accuracy, this paper developed a new T-junction models in which compressibility of gas flow was taken into consideration. A particle image velocimetry (PIV) test rig was established to provide data for investigating influences of flow parameters on the flow state and thermodynamic parameters in the T-junction. The results show that there are obvious streamline contractions in the internal flow field of the junction, and the formed boundary streamline divides the junction into two regions, as the flow ratio increases, the absolute value of the vorticity increases, and the vorticity in most areas of the branch joint is zero. In addition, the flow ratio of the branch pipe and the main pipe and the Mach number of the outflow affect the flow of the junction. Based on the results of the PIV test, a new pressure loss coefficient T-junction model for compressible flow is proposed. The new model has good prediction accuracy of the pressure loss coefficient and the prediction accuracy of the exhaust pressure wave increases by 4.43% when the pressure coefficient model is used in one-dimensional simulation program.