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Description
The effect of a cross-stream jet applied to the turbine nozzle guide vane (NGV) on the flow in a rotor-nozzle turbine stage is studied. A parametric study is conducted on the impact of jet location. Preceding the jet flow investigation, two commercial software programs, including Ansys CFX and Ansys Fluent, are assessed for the simulation of a generic turbine NGV flow with Reynolds Averaged Navier-Stokes models. The NGV computations are conducted for two operating conditions. The results for several turbulence models that are available in both CFX and Fluent are tested, including the k − , k − ω, and k − ω transition shear stress transport (SST) turbulence models. The pressure and temperature fields outside the boundary layer region display only minimal differences between the softwares and models. The prediction of transition locations in the boundary layer show significant differences. Despite meeting resolution requirements, CFX’s scalable wall functions predicts erratic and wrong boundary layer behavior. Because the performance of the softwares is comparable and because CFX has grid generators specially designed for turbine blades and an unsteady simulation capability for rotor-nozzle stages, we choose CFX for further simulation. The cross-stream jets are modeled as point sources and are placed at several locations on the suction side and pressure side of the NGV. The suction side jets induces flow separation, which in turn reduces the effective nozzle throat area. A trailing edge jet applied to the pressure side alters the Kutta condition of the nozzle. This leads to a more favorable angle of attack for the rotor. A combined pressure and suction jet flow increases flow turning of both the nozzle and rotor, improving lift and at some locations, reducing drag for the rotor.
