Accession Number : ADA334703

Title :   The Effect of Interaction on Boundary-Layer Separation and Breakdown

Descriptive Note : Final rept.

Corporate Author : AIR FORCE RESEARCH LAB BOLLING AFB DC

Personal Author(s) : Cassel, Kevin W.

PDF Url : ADA334703

Report Date : DEC 1993

Pagination or Media Count : 254

Abstract : It is common in boundary-layer flow at high Reynolds numbers involving separation for an interaction to be provoked between the viscous boundary layer and the inviscid external flow. The effect that this viscous-inviscid interaction has on both steady and unsteady boundary-layer separation is investigated. In part 1 the unsteady boundary-layer separation process is considered in the context of two-dimensional incompressible flow. In regions of adverse streamwise pressure gradient along solid surfaces, it is common for the boundary layer to erupt away from the surface in a narrow streamwise region. Classical non-interacting boundary-layer solutions of such flows breakdown within a finite time, but the thickening boundary layer induces an interaction with the outer inviscid flow during the first interactive stage in order to relieve the singularity. Numerical solutions were obtained of the first interactive stage formulated in Lagrangian coordinates. These results show that the viscous-inviscid interaction causes the flow to become unstable, resulting in a breakdown of the first interactive stage. The instability is of a high-frequency inviscid type and is shown to be characterized by large complex wavespeeds. In part 2 separation of a hypersonic boundary layer flowing over a compression ramp is considered, both with and without wall cooling. For small ramp angles, the flow in the vicinity of the corner is governed by the triple-deck structure which accounts for the viscous-inviscid interaction. The flow over the compression ramp exhibits separation in the corner for ramp angles above a critical value. Numerical solutions have been obtained for the hypersonic triple deck and show that for larger ramp angles the flow becomes unstable in the form of a stationary wave packet which forms near the corner.

Descriptors :   *FLOW SEPARATION, *BOUNDARY LAYER FLOW, PRESSURE GRADIENTS, ALGORITHMS, THESES, VORTICES, COMPUTATIONAL FLUID DYNAMICS, FLOW FIELDS, TWO DIMENSIONAL FLOW, UNSTEADY FLOW, INVISCID FLOW, VISCOUS FLOW, REYNOLDS NUMBER, INCOMPRESSIBLE FLOW, BOUNDARY LAYER CONTROL, HYPERSONIC FLOW.

Subject Categories : Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE