Abstract
Pump-turbines were always running at partial condition with the power grid changing. Flow separations and stall phenomena were obvious in the pump-turbine. Most of the RANS turbulence models solved the shear stress by linear difference scheme and isotropic models, so they could not capture all kinds of vortexes in the pump-turbine well. At present, partially-averaged Navier-Stokes (PANS) model has been found to be better than LES in simulating flow regions especially those with less discretized grid. In this paper, a new nonlinear PANS turbulence model was proposed, which was modified from RNG k-ε turbulence model and the shear stresses were solved by Ehrhardt's nonlinear methods. The nonlinear PANS model was used to study the instability of “S” region of a model pump-turbine with misaligned guide vanes (MGV). The opening of preopened guide vanes had great influence on the “S” characteristics. The optimal relative opening of the preopened guide vanes was 50% for the improvement of the “S” characteristics. Pressure fluctuations in the vaneless space were analyzed. It is found that the dominant frequency at the vaneless space was twice the blade passing frequency, while the second dominant frequency decreased as the preopening increased.
Highlights
Pump-turbine, which was one of the key components in a pumped storage power station, played an important role in the optimization of power network
For predicting the fluctuation of the dominant scale of vortexes, the traditional Reynolds-averaged Navier-Stokes (RANS) method suffers from inherent physical limitations [1, 2], which could not capture the flow with all kinds of scales
The simulation results of the “S” characteristics with synchronized guide vane (SyV) based on partially averaged Navier-Stokes (PANS) model agree well with experimental data
Summary
Pump-turbine, which was one of the key components in a pumped storage power station, played an important role in the optimization of power network. The study of instability of a pump-turbine should overcome the difficulties in the simulation of strong vortex and separation flow. For predicting the fluctuation of the dominant scale of vortexes, the traditional Reynolds-averaged Navier-Stokes (RANS) method suffers from inherent physical limitations [1, 2], which could not capture the flow with all kinds of scales. Speziale [5] proposed a new turbulence model that combines the advantages of RANS method with those of LES [6]. Partially averaged Navier-Stokes (PANS) model has been found to be better than that of the LES in flow regions where simulations suffered from poor near-wall. The instability of a pump-turbine was studied by the nonlinear PANS model
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