The flow structures of a variable geometry turbine at operating conditions of different nozzle open positions were investigated through CFD simulations. The flow field structures of the VGT at highly off-design operating conditions were presented. The evolution of the secondary flow vortex structures was studied. CFD results show that at open nozzle position, there is a recirculation zone on the nozzle vane pressure surface, and the rotor blade is under a considerable negative incidence, which leads to a passage vortex on the pressure surface of the blade. At closed nozzle position, the flow into the rotor has positive incidence, which leads to a recirculation zone on the suction surface. At highly off-design conditions, the passage vortex caused by the misalignment of the rotor inlet flow angle and the rotor blade angle accounts the most important losses of turbine flow. The turbine flow was controlled by adjusting the blade inlet angle distribution along the leading edge while keeping the radial-fiber rotor construction. CFD simulations show that the turbine efficiencies are improved in most operating points at both open and closed nozzle conditions.

This content is only available via PDF.
You do not currently have access to this content.