FLOW VISUALIZATION
FOR SUPERSONIC FLOW PAST A WEDGE
The Mach 4.0 nozzle will be used in the supersonic wind tunnel. This permits the use of
the top mounted sting to support models (wedge, cone, blunt body). The wedge used is
approximately 29 degrees total angle and can be mounted at various angles to the flow.
Each surface of the wedge has a static pressure tap (or several connected taps).
1. Instrumentation
(a) PSI pressure measurement system and computer
(b) Optics for schlieren and/or shadowgraph
(c) Nikon Digital camera
2. Measurements
(a) Static wall pressures on the wedge surfaces at three model angle settings (0, 5, 10
degrees).
(b) Settling chamber stagnation pressure
(c) Schlieren and shadowgraph photos of the wedge mounted in the test section. A test
model (wedge) will be installed in the test section in the optical path to produce an
oblique shock. “Mach lines” from the top and bottom tunnel walls will also be present.
The schlieren and/or shadowgraph mirrors, light source and slit should already be
aligned. If necessary, adjust the schlieren knife edge and camera. Obtain schlieren
and/or shadowgraph pictures during supersonic operation. Each student will receive
digital photos for each angle of attack.
Schlieren and Shadowgraph Methods
General Description
Optical methods are very powerful and relatively simple ways of studying supersonic
flows. Such flows involve large density changes which lead to large changes in the index
of refraction. Uniform light beams will be distorted by the index of refraction changes,
providing visualization of the flow features. Read one or more of the listed references
that are ON RESERVE IN THE LIBRARY.
A double-mirror schlieren and/or shadowgraph system, like the one shown in figure 1 is
set up in the supersonic lab. The mirrors are spherical, axial mirrors, 11.75 inches in
diameter with a focal length of approximately 82.4 inches. An additional plane mirror
“folds” the optical path located on the camera side. The light source and knife-edge
should be located on the opposite sides of the collimated optical path and as near as
possible to it to minimize the off-axis aberrations (coma and astigmatism). The light
source is a 1-2 microsecond General Radio Strobatac which can be remotely triggered
with a cable switch (button).
The schlieren is sensitive to the spatial derivative of density (and thus index of
refraction) in the flow field. A shadowgraph is sensitive to the second derivative of the
density, so it displays sharp variations, as across a shock, more clearly. All originating
