Parks College Parachute Research Group

Accelerating Disk Drag: Theory and Applications

J. Potvin
Saint Louis University, St. Louis, MO 63103

Presented at the 20th AIAA Applied Aerodynamics Conference, St. Louis, MO, June 24 -26, 2002, Paper AIAA-2002-3055




Abstract

We present a new model of the drag force generated by bluff bodies accelerating in a static fluid, and also accelerating in a headwind or decelerating in a tailwind, while sustaining an external force proportional to acceleration. Specific equations for the evolution of the drag coefficient are derived from the disk tow tank data of Iversen and Balent (Journal of Applied Physics, 22, pp. 324 - 328, 1951). Expressions for the drag force caused by motions in a tailwind and in a headwind are then derived using Galilean transformations of the tow tank data, which involved a static fluid environment far ahead of the moving disk. Application of these results to powered disk-like bodies are discussed. The validity of applying disk data to other bluff bodies is shown to be strongly dependent on the acceleration modulus. Prandtl's mixing length hypothesis is used to derive a useful formula from which this assessment is made. Finally, the issue of dynamical similarity for turbulent flows is revisited and extended to account for the unsteadiness of the flow that exists ahead of the disks.



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