Investigation of Wells turbine performance using 3-D CFD

The aerodynamics of the Wells air turbine has been studied using a three-dimensional, unstructured mesh flow solver for the Reynolds-averaged Navier-Stokes equations. Calculations have been performed for a monoplane device comprised of six blades at a stagger angle of 90 degrees under the conditions: Reynolds number equal to 8×10⁵, tip Mach number 0.4, solidity 0.5 and hub to tip ratio 0.6. Four flow coefficients representative of low, medium and high loading conditions have been considered. It is shown that the method is able to predict with reasonable accuracy the variation of pressure drop across and efficiency of the turbine with flow coefficient. However, stalling of the device is predicted too early. It is suggested that, counter to the received wisdom, the effect of the tip clearance flow is more significant in the process of turbine stall than the flow at the hub. The incidence at the hub is actually lower than at the tip, and it is hypothesized that this is due to the higher local solidity at the hub