Numerical Investigation of Ekman Layer Transition in Rotating Flows

Abstract This study relates to laminar-turbulent transitions in Ekman layers within high-pressure compressor (HPC) disk cavities, a critical aspect for optimizing gas turbine performance and heat transfer management. Using Direct Numerical Simulations (DNS), the research focuses on the transition mechanisms in radial outflow in rotating cavities, emphasizing the effects of noise and geometric modifications such as grooves. The results demonstrate that absolute instability governs the transition in steady Ekman layers on plane discs. The addition of a groove with a depth equal to the thickness of the Ekman layer significantly advanced the onset of turbulence. In the grooved configuration, instability emerges at r/b = 0.47, compared to r/b = 0.62 the smooth case, corresponding to a 43% reduction in the local rotational Reynolds number (Rer=ωr2v). White noise primarily influences the early convective instability phase, it has minimal impact on the absolute instability region, where flow dynamics remain unchanged. Conversely, the groove enhanced turbulence intensity by promoting the breakdown of large-scale vortices into smaller structures, amplifying shear stress, and increasing core tangential velocity to agree with measurement. These findings highlight the critical role of flow disturbances on transition and the potential role of geometric features in modifying instability mechanisms, offering insights into turbulence control strategies for thermal performance in rotating disk systems. Future studies will further explore the combined effects of surface modifications on flow stability and heat transfer in HPC cavity configurations.