![]() Stage 1 is the triggering phase which is brought about by the adverse pressure gradient on the suction surface between the location of maximum thickness, i.e., the shoulder, and the trailing edge (TE). This leads to the evolution of reverse flow within the boundary layer, which at this stage is still non-interactive. The separation bubble forms on the suction surface, which is undergoing a prescribed motion. Here, the unsteady flow separation is best characterized by zero apparent vorticity at the surface. Vorticity is invariant with respect to the moving coordinates, and hence, the need for an equivalent Moore-Rott-Sears (MRS) criterion can be avoided. In stage 2, the vorticity generated near the wall accumulates in the separation bubble which grows. This region is further characterized by sharp local pressure changes and the onset of interaction with the outer flow. Next, in stage 3, a strong interaction develops between the separation region and the outer inviscid flow region, and the accumulated vorticity within the separation bubble erupts as a double-sided vorticity layer. The time scale of this eruption is of O(Re −2/11) which is a very fine scale for high-Re flows. Finally, in stage 4, there is viscid-inviscid interaction as the free shear layer emanating from the leading edge (LE) experiences Kelvin-Helmholtz instability, rolls up and is sheared off by the erupting vorticity plume, to form an energetic dynamic stall vortex.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |