Laminar-Turbulence Transition over the Rotor Disk in an Enclosed Rotor-Stator Cavity

Abstract

Large eddy simulation (LES) of transitional and turbulent flow are performed for a range of rotational Reynolds numbers, 4 × 104 ≤ Reω = b2ω/ν ≤ 4 × 105, in both an enclosed rotor-stator annular and an enclosed rotor-stator cylindrical cavities of aspect ratio G = (b − a)/h = 5, where a and b are, respectively, the inner and outer radii of the rotor disk and h is the distance between the rotor and stator disks. Although it is well-known that the Cross-Flow instability plays an important role in the transition process to turbulence in the rotor boundary-layer, the spiral patterns related to the Streamline-Curvature (S-C) instability became dominant in this study. In addition, the structures due to secondary instability appear in the outward side of the primary spiral patterns. These structures obtained from LES are in agreement with experimental visualizations performed in this study. The results suggest that S-C instability is excited and becomes dominant in the rotor side since the rotor boundary-layer is perturbed by disturbances emanating from the stator side. Subsequently, secondary instabilities result from the interaction of the dominant S-C instability with the main flow. These instabilities seem to be the probable source of laminar-turbulence transition in the rotor boundary-layer for the present case.