Rolling Hills Research Corporation
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has developed a comprehensive set of classroom experiments for the
University Desktop Water Tunnel that demonstrate the basic principles of
fluid dynamics. Each experiment includes a ready-to-use model and detailed
documentation describing the underlying theory and presents
illustrations of sample results. New for
2014: the second generation of the prepared experiments is now
available. The model coatings have been improved for longer model life.
The interior routing of the dye tubes has been refined to better balance
the dye flow out of all of the surface dye ports.
experiment requires a model support system to conduct the tests. RHRC offers two different model support systems for the University
Desktop Water Tunnel: a sting mount, and a wall mount.
is a description of the model support systems and the five classroom
experiments that are currently offered.
experiment documentation is included separately with each experiment
purchased. When purchased as a set, the four experiments, the
dye wand and the model mounts come in a protective case. Below is a brief description of the four experiments that are
A dye wand is
available to help visualize streamlines and streaklines in the flow. The
dye wand has a fairing that reduces the interference from vortices shed
from the tube. The dye wand is normally mounted in a pair of holes
located just upstream of the test section. The wand may also be attached
at any of the wall mount screw locations. The position of the dye wand
can be adjusted by loosening either of the two thumb screws and sliding
the wand up and down or side to side. Any of the three colors of dye can
be connected to the wand.
cylinder experiment consists of two long cylinders, one with dye ports
that is stationary, and one without dye ports that rotates about its
center axis. The stationary cylinder is used to show the regular pattern
of shed vortex “streets”. The dye wand is positioned upstream to
show the difference in the streamlines with and without rotation, and
provides an explanation of how lift is produced.
visualize the circulation influence of the rotating cylinder. It is
instructional to compare these streamlines to those observed with the
airfoil experiment shows not only the streamlines associated with a
lifting surface, but also the way it is effected by changes in
angle-of-attack. Surface dye ports are used to show the boundary layer
separation behavior that occurs as the angle-of-attack is increased.
forebody/projectile experiment demonstrates the extremely strong vortex
pair that is created in the wake of a cylindrical body at high
angles-of-attack. This type of flow field plays a very important part in
the directional stability and control of aircraft and missiles at high
angles-of-attack. Small asymmetries or miniature control strakes can
cause these vortices to become very powerful side force and yawing
delta wing aircraft experiment is a fine example of a vortex dominated
flow field. Very important parameters such as the vortex burst position
are clearly visible, and can be studied as a function of
angle-of-attack, sideslip and roll angle. The model has a removable
vertical tail and moveable control surfaces. The experiment write-up
discusses not only the non-linear aerodynamics, but also the roll of
vortices in limit cycle motions such as wing rock.
sting mount is machined from aluminum and anodized to protect it from
corrosion. The entire assembly bolts to the top of the water tunnel test
section with two screws. There is only one position in the tunnel that
the sting can attach, and it is located at the furthest downstream
position. This locates the model near the center of the test section.
Each experiment that uses this mount comes with its own sting. The sting
slides into a mounting adapter on the C-strut, and is secured by two set
screws. If a homemade experiment is to be mounted on the C-strut, the
sting should be made of ¼” stainless steel rod. The C-strut can be
locked in position by two small thumb screws, which must be loosened in
order to adjust the position without damaging the assembly. The C-strut
can be manually rotated with a small knob, which is attached to a gear,
that meshes with a rack on the C-section.
C-strut has engraved marks every 5º
to indicate the model angle-of-attack. An
additional line is etched on the clamping portion of the support and is
used to indicate the zero position, as determined in RHRC's lab. Both
the matching zero lines are tagged with a light blue paint dot. This
pointer is calibrated to indicate the position where the sting would be
parallel to the tunnel flow. In addition, a stick-on pointer can be used
to indicate any other reference desired. If a different reference point
is desired, a new sticker may be applied. The C-strut provides an angle
range of approximately -35º
to +50º. In order to achieve
even higher angles of attack, the adapter that attaches the sting to the
C-strut can pivot upward an additional 15º.
To change the adapter angle, simply loosen the two screws, pivot the
adapter, and re-tighten the screws. In addition, the angle-of-sideslip
can be adjusted by loosening the thumb screw on the top of the mount. An
angle indicator shows the angle-of-sideslip.
wall mount is made primarily of clear plastic so that it won't obscure
the view of the test section. Because of this material choice, the wall
mount should be handled with care to avoid damaging it. There are two
configurations possible with the wall mount: push-rod adjustable
angle-of-attack, and continuous rotation. Experiments such as RHRC's
Rotating Cylinder use a pulley and hand crank to provide rotation.
Experiments like an RHRC's Airfoil use a push-rod control for
adjusting discrete angles-of-attack.
wall mount is composed of two major pieces, one for each side of the
tunnel. The most complicated piece, the one containing both the hand
crank and the push-rod, is mounted on the side of the tunnel opposite
the speed control. Two screws attach each side to the tunnel, which are
accessed through holes in the top of the rectangular, black, mounting
frame. There are two mounting positions available for the wall mount,
one in the front of the test section for observing wake behavior, and
one near the center of the test section. Experiments are attached to the
wall mount by sliding the stainless steel pivot pins into the ball
bearings at the bottom of the wall plates. The experiment must be
mounted on the wall mount before the mount is attached to the tunnel. In
the case of the rotating cylinder, the rubber drive belt must be put in
position before the pin is slid into the bearing. The push rod should be
connected by sliding it over the appropriate control pin on the model,
for non-rotating experiments, prior to installation in the tunnel as
purchased as a set, the four experiments, the dye wand and the model
mounts come in a protective case.