Parks College Parachute Research Group

Experimental Study of Fluid-Structure Interactions on a Cross Parachute: Comparison of Wind Tunnel Data and Drop Data With CFD Predictions

J. Potvin, L. Esteve, B.Brocato, and G. Peek - Parks College Parachute Research Group
R. Alamat and J. Little - Paranetics Technology Inc.
Richard Benney and Keith Stein - Soldier Systems Command, U.S. Army Natick Research, Development, and Engineering Center

Presented at the 15th AIAA Aerodynamic Decelerator Systems Conference, Toulouse, France, June 9-11, 1999



Abstract

A series of wind tunnel tests was recently funded by the U.S. Air Force to study the feasibility of a "drogue-to-main" cruciform parachute system to be used in ballistic cargo airdrops of the HALO type. Although most of that effort has concentrated on the design of such a system and on a wind tunnel study of several drogue-to-main concepts [1], a significant amount of work has also been invested in the comparison of wind tunnel results with data of a CFD simulation of the same wind tunnel experiment [2].

The comparison was also extended to data gathered during actual drops from a flying ram-air parachute of the same wind tunnel model with data of an "open air" CFD simulation. Comparing wind tunnel data with CFD data should be beneficial to both methods of parachute study since, on one hand, it helps validating the algorithmic approximations and turbulence modeling used in CFD codes, and on the other hand, help researchers understanding the details of wind tunnel systematic errors such as model blockage, wall boundary layer effects and parachute model construction [3, 4].

The comparison is focusing on the measurement of the drag force generated by a standard cruciform parachute built out of two 1 ft -by- 3 ft panels, and of its surrounding pressure environment. The comparison is performed in a speed range of 8 to 80 mph. As discussed in more details in reference [1], the wind tunnel is of an open-type, featuring a 55"-long, 40"-deep and 28"-tall test section in which wind speeds of up to 120 mph can be reached. In order to improve our understanding of the effects of construction details on parachute inflated shape, several materials were used to build the models, including low and high permeability fabric, spandex webbing and nylon tapes. Photographs of the model parachutes used can be seen here.

The paper will present and discuss the following results:

1) measurements of the tunnel's flow quality (as defined in reference [5]);

2) comparison of parachute drag areas obtained from test drops and "open air" CFD simulations (speed range 8 to 50 mph; zero-porosity parachute);

3) comparison of parachute drag area and pressure distribution obtained in the wind tunnel and in CFD simulations of the same experiment (speed range 40 to 100 mph; zero-porosity parachute);

4) comparison of the drag area generated by models made of different fabric and reinforcing tapes.

Acknowledgements

The authors are grateful for the invaluable help provided by Mr. M. Barcklage. We are also grateful to Professor K. Ravindra and Mr. F. Coffey from the Department of Aerospace and Mechanical Engineering, Saint Louis University, for their aeronautical and tunnel expertise. Finally, the authors want to thank the U.S. Air Force Office of Scientific Research for providing the financial support so vital to these experiments.

References

1. Potvin, J., Esteve, L., Peek, G. and Alamat, R.; "Wind Tunnel Study of Cruciform Parachutes Folded in Various Configurations"; this conference; AIAA-99-zzzz.

2. Stein, K., Benney, R., Kalro, V., Tezduyar, T., Bretl, T. and Potvin, J.; "Fluid-Structure Interaction Simulation of Cross Parachute: Comparison of Numerical Predictions with Wind Tunnel Data"; this conference; AIAA-99-xxxx.

3. Macha, J. M.: "An Introduction to Testing Parachutes in Wind Tunnels"; AIAA-91-0858.

4. Rae, W. H. and Pope, A.; "Low-speed Wind Tunnel Testing"; 2nd ed., John Wiley and Sons, New York 1984.

5. Saric, W. S. and Reshotko, E.; "Review of Flow Quality Issues in Wind Tunnel Testing"; AIAA-98-2613.



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