Modeling Vortices in an Aqueous Medium

Presented by

Brady McDaniel

Colorado State University

Sound and Vibrations REU

in Collaboration with Dr. Bogusz Bienkiewicz

Made Possible Through the Cooperation and Funding of

Colorado State University, The National Science Foundation,

And The Army Research Office

This research projects objective was to develop a prototype that could be used to easily visualize vortices similar to the eye/eyewall of a hurricane and that of a tornado. Taking previous breakthroughs in the field by Montgomery, Vladimirov, and Denissenko (2002), and Whitehead and Porter (1978) and forming a smaller and more versatile model that could be used for teaching and experimental purposes accomplished these objectives.

The prototype works by taking water and introducing swirl or vorticity in the water by moving it in a centrifugal motion at a high speed (500 gallons per hour). This water then flows underneath a circular disk with a hole inscribed in its center, which creates a semi-slip condition. The water then flows through the circular hole of the sink and into the lower chamber. In the middle of the lower chamber there is honeycomb placed in the center in order to suppress vortical motions generated from the sink. The water then flows from the lower chamber into the overflow bucket, which catches the water and holds it there so that it can be pumped back into the system using the re-circulating sub-pump.

A key component to the prototype is the ascending return flow from the lower chamber up into the sink. In order to get the return flow it is imperative that the lower chamber is flooded which is easily obtainable since the inflow is greater then the outflow. The return flow is due to the fact that the swirling fluid in the sink has a lower pressure in its center then there is in the lower chamber. When the collision between the centrifugal flow and the flow coming up from the lower chamber is not resistant to disturbances multiple vortices are created when they are stabilized a single vortex is produced.(Lugovtsov 1982)

In most of the tests that were run a single vortex was developed. When a disturbance was presented it was observed that the flow would recover to a single vortex flow rapidly as the flow stabilized itself. Multiple Vortices were only visualized a couple times and for a limited time period. More time would be needed to find the correct swirl ratio for the given conditions that would sustain a continuous multiple vortex flow. It was also observed that the vortices needed to be viewed upside down in order to see how they would look in nature. This is due to the fact that the suction is coming from gravity, which is on the bottom in the prototype however in nature it comes from the top from a thunderstorm or by the internal energy sources for a tornado or hurricane respectively. The smaller skinnier vortices of a tornado were modeled by covering a greater amount of the hole in the sink thus mimicking the vortex of a tornado. A final observation was when a piece of Plexiglas was used to cover the hole in the sink a greater amount of suction was created. When that Plexiglas was slowly raised up from the hole a vortex formed onto the Plexiglas instead of going down the hole a 180-degree shift from the normal nature of the model. This Phenomenon needs to be studied more to see if this prototype can be used to model vortices that can be viewed in the same directions as those found in nature.

Clockwise from left to right: A hurricane eye/eyewall simulation at a normal depth using the prototype and a tornado simulation when the hole in the sink was covered partially.

Clockwise from left to right: The prototype when viewed from above and when viewed from the side.

References:

Lugovtsov, B.A., 1982: Laboratory models of tornado-like vortices. Intense Atmospheric Vortices, ed. by Bengtsson/Lighthill, Springer-Verlag.

Montgomery, M.T., Vladimirov, V.A., and Denissenko P.V., 2002: An Experimental Study on Hurricane Mesovortices. Journal of Fluid Mechanics, 9-18.

Whitehead, J.A. Jr., and D.L. Porter, 1978: Axisymmetric critical withdrawal of a rotating fluid. Dyn.Atmos. Oceans,2,1-18.