A STUDY OF FLOW BEHAVIOUR IN RADIAL AND MIXED FLOW TURBINES WITH VARIABLE NOZZLE VANES FOR A TURBOCHARGER

摘要

A mixed flow turbine with variable nozzle vanes is developed along with its radial counterpart for the wheel size of about 30 mm, suitable for turbocharger of 1.5 lit. engine capacity. In order to understand the flow behaviour inside the turbines, computational fluid dynamics studies are conducted for both the radial and mixed flow turbines. Flow through the turbine stage is discussed with velocity distribution in the meridional plane. In addition, the loss coefficients for the nozzle vanes and turbine wheel are estimated. At nozzle vanes opening of 50% mass flow parameter and for the turbine expansion ratio of 1.5, the flow velocities at the exit of the nozzle vanes are found to be about 120 to 170 m/s for the radial flow turbine and 150 to 180 m/s for the mixed flow turbine. Higher level of uniformity in flow is also observed for mixed flow turbine stage compared to the radial. The maximum Mach number is observed on the middle of the turbine wheel, and the same is less than unity for both the turbines. Both the nozzle and rotor loss coefficients for mixed flow turbine are lower than the values observed for the radial flow by about 6% and 15% respectively.