Separation of a supersonic boundary layer, or equivalently a hypersonic
boundary layer in a region of weak global interaction, flowing over a
compression ramp is considered. For small ramp angles, the flow in the vicinity
of the corner is governed by the classical supersonic triple-deck structure
which accounts for 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 supersonic triple deck and show
that for larger ramp angles the flow becomes unstable in the form of stationary
wave packet which forms near the corner.
Funded by: Air Force Office of Scientific Research and National Defense Science and Engineering
Graduate Fellowship
Hypersonic boundary-layer separation on a cold wall is considered with
particular emphasis on the effect of the wall cooling on separation and the
instability observed in Cassel, Ruban and Walker (1995). The flow is characterized by two parameters:
one related to the level of wall cooling and another which depends upon the
average Mach number across the boundary layer. The sign of the latter
parameter determines whether the flow is subcritical or supercritical.
Numerical solutions were obtained for both subcritical and supercritical
boundary-layer flows over the compression ramp geometry with various ramp
angles and levels of wall cooling. Wall cooling of subcritical boundary layers
was found to have a strong destabilizing effect, and wall cooling of
supercritical boundary layers was found to have a stabilizing effect. The
effect of wall cooling on separation is also dramatic and depends upon whether
the boundary layer is subcritical or supercritical. If the boundary layer is
subcritical, wall cooling limits the downstream influence of the ramp, and if
the boundary layer is supercritical, wall cooling limits the upstream influence
of the ramp. In either case a sufficient level of wall cooling was found to
eliminate separation altogether for the ramp angles considered. In addition,
comparisons between the present numerical results and the strong wall cooling
case considered by Kerimbekov, Ruban and Walker (1994) are given and appear to
confirm their scalings for the strong wall cooling case.
Funded by: Air Force Office of Scientific Research, NASA Lewis Research Center and National Defense Science and Engineering
Graduate Fellowship