Impact by double scroll on variable geometry turbine performance

Abstract

Abstract This paper describes the numerical study for the development of a double scroll(DS) turbine stage combined with a variable geometry system (VGS). Our conventional VGS turbine stage is composed of a mono-scroll housing, variable nozzles and a turbine wheel. A potential to improve engine performance by applying a DS with VGS turbine stage (DS-VGS) was shown by the study. In addition, a DS-VGS has some advantage in the layout for V type engine. Therefore, this study has focused on clarifying the characteristics of aerodynamic performance of a DS-VGS, since the understanding of these fundamental characteristics is important for product development. The differences of performance between a mono-scroll with VGS and a DS with VGS were evaluated as the starting point. In the development for a vaneless DS turbine so far, it has been clarified that the distance from tongue to turbine wheel is one of the important parameters for performance. Therefore, numerical simulations were performed with different tongue-to-nozzle distances. Further, from reliability point of view, the influences of a DS on nozzle moments and aerodynamic forces on nozzle have been examined. The interesting characteristics of a DS-VGS compared to a mono-scroll with VGS are shown.