Research On Aerodynamic Axial Force Of Turbocharger Under Different Operating Conditions Of Engine

From the initial development to wide application,turbocharger has become a core technology of fuel vehicles.The aerodynamic axial force is also one of the important factors affecting the stability,efficiency and reliability of turbocharger,and its formation mechanism is the focus and difficulty in the field of turbocharger research.Therefore,this paper discusses the internal flow mechanism of turbocharger and the influence of engine operating conditions on the aerodynamic axial force of turbocharger.According to one-dimensional model of an engine built by GT-power,the inlet and outlet parameters of turbocharger under steady and unsteady conditions are obtained by numerical simulation.The three-dimensional flow numerical simulation of turbocharger is carried out by CFX with the modified parameters as the boundary conditions for three-dimensional calculation,aiming to analyze the internal flow and aerodynamic axial force of turbocharger.The following rules are obtained:There exists difference between pressure distribution of compressor blades under unsteady condition and steady condition,which is caused by restrained Coriolis force from vortices.The meridional streamline analysis shows that the intensity of the vortices varies only in the radial direction.In other words,the limit streamline of the case has a dense flow at the top of the blade under steady state;whereas it appears a clear boundary and a reverse rotating flow at the entrance with high load under unsteady state.Under different operating conditions,there is little difference between the steady-state pressure distribution in turbine and the unsteady-state of it.The axial force of turbocharger is composed of wheel back force,blade force and hub force.The blade force obtained under unsteady condition is quite different from that under steady condition in both numerical value and variation trend,for the reason that generation of vortices restrains the action of Coriolis force.Under unsteady condition,the variation trend ofblade force is fluctuated due to the unbalanced axial pressure of blade;and the change of wheel back force is mainly affected by clearance leakage flow.In this case,the influence of rotational speed and load on leakage flow is greater than that under steady state condition.Moreover,the change of hub axial force is consistent under both steady and unsteady conditions;while the difference of axial resultant force is existed between steady and unsteady conditions,among which the difference of wheel back force is the dominant factor.