Effects of location of excitation on the spiral vortices in the transitional region of a rotating-disk flow

Abstract

The laminar-turbulent transition of a rotating-disk flow dominated by global instability is studied by solving the full Navier-Stokes equations in direct numerical simulations. A flow field in the 2π/32 region is computed using a periodic boundary condition. The flow field is disturbed in two ways. In the first case, a disturbance is introduced at the Reynolds number, Re≈ 600, while in the second case, a disturbance is introduced at Re≈ 650. In both cases, wall-normal short-duration suction and blowing are used to disturb the flow field. When a disturbance is added upstream at Re≈ 600, the wavenumber 64 component becomes dominant when the flow reaches a steady state, whereas when a disturbance is added downstream at Re≈ 650, the wavenumber 96 component becomes prominent. The transition points are different between the two cases. In addition, in both cases, the distances between neighboring spiral vortices are quite the same when measured at the locations where the turbulence begins.

An adjoint approach for computing the receptivity of the rotating disc boundary layer to surface roughness

“…Since absolute instability and transition to turbulence occur within the same band of Reynolds numbers, Lingwood (1996) suggested that the absolutely unstable mechanism is the primary cause for the breakdown of the laminar flow. Several recent investigations on a rotating disc of finite radius suggest that absolute instability can establish globally unstable behaviour if disc edge effects are accounted for (Healey 2010;Imayama et al 2013;Pier 2013;Appelquist et al 2015Appelquist et al , 2016Lee et al 2017Lee et al , 2018. Additionally, Pier (2003) suggests that a secondary absolute instability develops near the primary absolute instability, providing an alternative route to turbulence.…”

Flow measurement around the edges and curved outer surface of a rotating disk

“…The flow structures on the flat surface of an infinite rotating disk in a still fluid are often explained in terms of flow instabilities (Lingwood 1995;Itoh 1996;Lee et al 2017). The surrounding fluid is sucked toward the disk surface and driven outward by centrifugal force.…”