Growth of Spiral Vortices in a Globally Unstable Region on a Rotating Disk

Abstract

Results: Four cases with azimuthal domain sizes of 2π/10, 2π/70, 2π/80 and 2π/90 are compared. In all cases, a short-duration wall-normal random suction and blowing is introduced from the wall at the beginning of the computation. In the computation for the wider size 2π/10 domain, wavenumber components of 70, 80 and 90 are all found to co-exist in the flow field, with the wavenumber 80 component being much stronger than the other two components. The strength of the wavenumber 80 component is equivalent to the narrower domain case. For the other two wavenumber components of 70 and 90, the strengths in the wider domain case are much lower compared to the corresponding narrower domain cases. When the same wavenumber components are compared between the wider and narrower domain computations, no difference can be found, indicating that each wavenumber component grows by the global instability.