PREDICTION OF THE STEADY AND NONSTEADY FLOW PERFORMANCE OF A HIGHLY LOADED MIXED-FLOW TURBINE

This paper describes a method for predicting the performance under bot h turbine inlet steady state and non-steady state flow conditions of a mixed flow turbine used for turbocharged internal combustion engines. The mixed flow turbine steady state performances computed with the st eady state performance prediction method are in good agreement with th e experimental results obtained in the Imperial College turbocompresso r cold air test rig. The unsteady state performance is computed using a one-dimensional model based on the solution of the unsteady one-dime nsional flow equations. These equations are solved in the volute by a finite difference method using a four-step explicit Runge-Kutta scheme . The instantaneous volute exit condition is provided by the steady st ate rotor performance prediction model with the assumption of a quasi- steady state flow in the rotor. The computed instantaneous performance s are in reasonable agreement with published experimental data for the same mixed flow turbine. The unsteady flow model is also used to stud y the effects of the frequency and the amplitude of the pulse on the p erformances of the mixed flow turbine.