Prepared Classroom Experiments 

RHRC 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.

Each 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. 

Below is a description of the model support systems and the five classroom experiments that are currently offered.

Class Experiments

Complete 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 currently offered.

Dye Wand

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

The 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.

Streamlines visualize the circulation influence of the rotating cylinder. It is instructional to compare these streamlines to those observed with the airfoil model.

Airfoil

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

The 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 moment producers.

Delta Wing Aircraft

The 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

The 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.

The 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

The 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.

The 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 well.

Protective Case

When purchased as a set, the four experiments, the dye wand and the model mounts come in a protective case.