Numerical study on three dimensional unsteady flow of a high pressure gas turbine stage

Unsteady flows such as wake flow, separated flow and shedding vortices are the main factors inducing the excitation force on turbine blades. To obtain the unsteady flow field in a high pressure gas turbine stage, the numerical model and calculation method have been developed by adopting RNG k- turbulence model, dual time step method, sliding interface model and structure grid. The complex unsteady pressure distribution on the rotor and stator blades are obtained and analyzed, which shows the stator/ rotor blade interference effect and reveals the source of unsteady aerodynamic blade force, then the pressure is integrated around the rotor blade profile to give the unsteady aerodynamic blade force, based on that data, frequencies of unsteady disturbances and excitation force factors are obtained by spectrum analysis. As shown in the plot of forces, the forces are sinusoidal periodic variation. The largest excitation force occurs at the frequency of 2000Hz, corresponding to the blade passing frequency. Meanwhile, the first order excitation force factor is also obtained, and it is agreement with the data which comes from Traupel method and engineering practice.