| The energy saving and CO2 emission reduction of internal combustion engine are of great significance.The technology of reducing the displacement is the main technology of energy saving for internal combustion engine.Turbocharging is the key to achieving reduced displacement.Turbine is the core component for energy recovery from the exhaust gas.Improving the turbine performance is important to the development of high-performance supercharging technology.Existing studies have shown that twin-entry turbine has great advantages on the transient performance and scavenging.In the actual conditions,the two limbs of the twin-entry volute are in partial admission conditions.Based on the full 3D CFD flow analysis,this paper develops the performance prediction model for twin-entry turbine and realizes the coupling with the performance model of the internal combustion engine.The main contents are as follows.According to the flow characteristics,the turbine is divided into three control surfaces:volute inlet,rotor inlet and rotor outlet.Based on the one-dimensional aerodynamics and thermodynamic theory,the basic performance prediction model is established.The model of turbine loss is discussed in detail.Losses in the volute include the pressure,swirl and blockage losses.Losses in the rotor include the incidence,rotor passage,clearance flow and disk friction losses.The detailed flow mechanism analysis of a type of self-designed turbine with twin-entry volute is carried out by means of full 3D CFD simulation under different partial admission conditions.The results show that rotor performance is higher in the case of shroud-in（SI）than hub-in（HI）.The flow mechanism analysis shows that the volute produces significant leaf height distortion in the rotor inlet under different partial admission conditions,which further transmits to the rotor and produces vortexes of different topologies near the leading edge of the rotor inlet.The vortex structure gradually evolves toward the rotor exit,leading to the formation of the vortex structure near the exit tip for HI.While the vortex structure is mainly gathered near the hub side of the rotor for SI,resulting in the higher increase of entropy for HI.The flow analysis shows the detailed flow characteristics of the exit field for twin-entry volute.Based on the analysis of the flow,a performance prediction model of twin-entry volute is established.Based on the experimental measurements and the CFD simulation results,the model is verified and verified.The results show that the flow capacity and efficiency of the single-entry turbine are in good agreement with the experimental results.The results of the twin-entry turbine model are compared with the CFD simulation data,and the results are in good agreement,which proves that the model has high reliability.At the same time,sensitivity analysis of the main model parameters is carried out based on the model.Finally,based on the characteristic line method,the boundary between the turbine model and the gas system of the internal combustion engine are processed.The model of turbine is coupled with the performance model of internal combustion engine.Based on the coupling model,the influence of the main geometric parameters of the turbine on the performance of the internal combustion engine are discussed. |
