Instability characteristics induced by roughness elements in the rotating-disk boundary layer of a rotor-stator cavity

This study targets the stability issues of rotating-disk boundary layer in a rotor-stator cavity within the context of the incompressible Navier-Stokes equations, incorporating a drag model representative of roughness elements. Consequently, 32 azimuthally uniformly distributed roughness elements have been positioned within the computational domain. Owing to the inviscid crossflow instability inherent to the rotating-disk boundary layer, the roughness elements induce crossflow vortices with an azimuthal wave number k=32. Upon saturation of the crossflow vortices, a transition to turbulence does not immediately ensue; instead, a series of azimuthal Fourier modes constituting self-sustaining, spatiotemporally coherent traveling spiral waves mode emerge downstream. At higher Reynolds numbers, these traveling spiral waves mode reach saturation and are followed downstream by a transition to turbulence. Notably, to the best of the authors' knowledge, this is the first instance where selective excitation of crossflow vortices with a specific wave number in the rotating-disk boundary layer within a rotor-stator cavity has resulted in a transitional process ultimately dominated by traveling mode spiral waves. This process is distinct from the one observed over a single rotating disk, where the crossflow vortices, after reaching a certain Reynolds number, govern the transition to turbulence in the von Kármán boundary layer. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)Flow instabilityRotating turbulenceTransition to turbulenceTurbulence