JK90S Variable Nozzle Turbine Shock Wave Characteristic Research

Variable nozzle turbocharger can effectively improve the performances, fuel economy and emission fuel economy and emission level of internal combustion engine and has an optimistic application prospect. Under high load operation points with large turbine expansion ratio, on certain sudden breaking conditions, the nozzle exit is often accompanied by strong shock wave, which introduces high frequency and strong exciting forces on the impeller. The exciting force can potentially lead to impeller high frequency fatigue. In order to investigate the shock wave behavior that introduces high frequency fatigue, numerical study on the JK90 S turbine is carried out and following studies are carried out:First, the steady state calculations are performed to validate the numerical methods used in current research. The flow field and turbine performances are experimentally validated.Second, based on the analysis of the unsteady, influences of the nozzle opening on the shock wave are investigated. The changes of the shock wave position and intensity under different nozzle opening and relative positions between nozzle trailing edge and impeller leading edge are thus analyzed in details. Results indicate that the shock wave always exists, with intensity changing depends upon the relative positions between nozzle trailing edge and impeller leading edge, and the position of the shock wave is shifted upstream against the nozzle.The intensity of the nozzle shock wave under 20 degree opening is weaker than 15 degrees opening, and the position of the shock wave is shifted downstream against the nozzle.Third, investigation of the wake flow and gap leakage flow in nozzle is carried out. The results show that gap leakage introduces high flow losses in the shroud and hub region. Nozzle wake travels downstream about 0.8 nozzle pitch. With the rotation of the impeller blade, wake flow is interrupted.Finally, the analysis of pressure distribution under different nozzle opening and nozzle gap is carried out. The results show that the fluctuations of static pressure occur near the blade leading edge, with a much higher magnitude on the suction side pressure fluctuations are more severe. Along the spanwise, major pressure fluctuations locate at the midspan of the impeller. Results also indicate that the clearance flow in the tip and hub region of the nozzle introduce additional pressure fluctuation on the impeller blade surface. Key words: turbine; variable nozzle; shock wave characteristics; nozzle opening...