Abstract
An improved low-Reynolds-number k-ε model is adopted to predict turbulent flows with a nonstationary boundary. The performance of the adopted model is first contrasted with direct numerical simulation data of the turbulent plane Couette-Poiseuille flow. Detailed flow structure is captured accurately by the model, in particular the reduction of the shear stress and, hence, the turbulent kinetic energy due to the presence of the moving wall. The validity of the present model in computing complex flows within rotating disk cavities is further examined. Flows with two different rotational Reynolds numbers are investigated, and the predicted mean and turbulence results are also contrasted with measurements. The influence of rotation on the flowfield and turbulence modeling is investigated by sensitizing the turbulence model coefficient to rotational Richardson number, and the effect is found to be marginal. Because the internal flow structure of the rotating disk cavities is induced by the diffusive transport of the tangential momentum from the rotor into the interior, the predicted thickness of the Ekman layer is found to be critical to the correct predictions. The adopted model reproduces correctly the gradual thickening of the Ekman layers from small to large radii, which is due to the transition from laminar to turbulent regimes, especially on the rotor side within the disk cavities. The elevated level of turbulence on the stator side compared to that on the rotor side is also predicted correctly by the present model.