Variable Nozzle Turbocharger Nozzle Design And Unsteady Flow Field Analysis

Due to its flow cross-section can change in working conditions, variable nozzleturbocharger can form a good match with vehicle. Thereby, it enhances engine power,acceleration and other properties more efficiently than other turbochargers. Thus it isincreasingly used in the vehicle engine. But the high-cycle fatigue of the rotor blade leadingedge to some extent hindered the further promotion of variable nozzle turbine. The shockwave, tip clearance leakage flow in turbine flow field are considered to be the main causeof failure, so the research of turbine vane channel flow and the change patterns of unsteadyflow phenomena becomes imperative. In this paper, the main work is done:In this paper, JK90S variable nozzle turbocharger’s nozzle had been modified tooptimize the design, and two kinds of retrofit solutions are made. The first program was toincrease the number of nozzle vanes to increase blade consistency, increasing the degree ofoverlap of adjacent blades to accelerate airflow longer distance. After the air got enoughpower, the air drove a turbine rotor in the nozzle channel. The second solution was tochange the nozzle vane type which had thick leading edge, this type can adapt to flow anglewhich always changes in resulting pulse supercharging.Numerical models were established for both programs and were verified the validity ofthem. Steady numerical calculations of the two turbines were completed, then, we got morecomprehensive characteristics. Then, we analysed unsteady flow field in order to explorethe various features of the unsteady flow characteristics and their impact on the turbine.Through the comparison of the rotor-static surface in the two programs, we found that thesecond airfoil’s flow acceleration was better, but also it appeared shock wave. Leaf type andthe degree of opening of the nozzle could affect the intensity and location, and also affectedthe flow field near the upstream of the rotor blades. Because of different blade types, wake’sintensity changed, the wake traveled along the circumferential direction and wouldn’t causea pneumatic impact on the rotor blades. Tip leakage flow of the two programs weredifferent in intensity. When it spread to the downstream, it would affect the flow fielddownstream of the rotor at the leading edge. With the rotation of the turbine, the regionalimpact would continue to change. Compared to the wake, shock wave and gap leakage flowhad more impact on the flow field in the downsteam, they both produced a strongdisturbance near the rotor blade leading edge. As to the second program had better performance, the program of this article nozzlewere manufactured, and the turbine characteristics tests were conducted. The test resultsshow that the flow range of the turbocharger of the second program became wider, it couldform better match with various engine operating conditions, and the ability of the nozzle toadjust the flow became stronger.