62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009;
Minneapolis, Minnesota
Session K1: Invited Session: Unsteadiness of Shock Wave / Boundary Layer Interactions
2:40 PM–3:15 PM,
Monday, November 23, 2009
Room: 205A-D
Chair: Alexander Smits, Princeton University
Abstract ID: BAPS.2009.DFD.K1.1
Abstract: K1.00001 : Unsteadiness of Shock Wave / Boundary Layer Interactions*
2:40 PM–3:15 PM
Preview Abstract
Author:
Noel Clemens
(The University of Texas at Austin)
Shock wave / boundary layer interactions are an important feature of
high-speed flows that occur in a wide range of practical configurations
including aircraft control surfaces, inlets, missile base flows, nozzles,
and rotating machinery. These interactions are often associated with severe
boundary layer separation, which is highly unsteady, and exhibits high
fluctuating pressure and heat loads. The unsteady motions are characterized
by a wide range of frequencies, including low-frequency motions that are
about two orders of magnitude lower than those that characterize the
upstream boundary layer. It is these low-frequency motions that are of most
interest because they have been the most difficult to explain and model.
Despite significant work over the past few decades, the source of the
low-frequency motions remains a topic of intense debate. Owing to a flurry
of activity over the past decade on this single topic we are close to
developing a comprehensive understanding of the low-frequency unsteadiness.
For example, recent work in our laboratory and others suggests that the
driving mechanism is related to low-frequency fluctuations in the upstream
boundary layer. However, several recent studies suggest the dominant
mechanism is an intrinsic instability of the separated flow. Here we attempt
to reconcile these views by arguing that the low-frequency unsteadiness is
driven by \textit{both} upstream and downstream processes, but the relative importance of
each mechanism depends on the strength (or length-scale) of separation. In
cases where the separation bubble is relatively small, then the flow is
intermittently separated, and there exists a strong correlation between
upstream velocity fluctuations and the separation bubble dynamics. It
appears that superstructures in the upstream boundary layer can play an
important role in driving the unsteadiness for this case. It is not clear,
however, if the upstream fluctuations directly move the separation point or
indirectly couple to a global instability. In cases where the separation is
strong (and the bubble large) then the bubble pulsates owing to a global
instability, as has been suggested by other researchers. In this case
upstream turbulence may serve mainly as a source of broadband fluctuations
that seed the large-scale instability of the separated flow.
*The author's work on this topic has been sponsored, over many years, by AFOSR and ARO. This support is gratefully acknowledged.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2009.DFD.K1.1