Effect of Compressibility at High Subsonic Velocities on the Moment Acting on an Elliptic Cylinder
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS LANGLEY FIELD VA LANGLEY AERONAUTICAL LABORATORY
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An extended form of the Ackeret iteration process is utilized to calculate the compressible flow at high subsonic velocities past and elliptic cylinder. The angle of attack with respect to the direction of the undisturbed stream is assumed small and the circulation is fixed by the condition that the trailing end of the major axis be a stagnation point. The expression for the moment acting on the elliptic cylinder is derived and shows a first-step improvement of the Prandtl-Glauert approximation. In addition, a second-step improvement is obtained in the Prandtl-Glauert approximation for the lifting force acting on the elliptic cylinder. By means of these two results it is possible to calculate the effect of compressibility on the position of the center of pressure as a function of the thickness coefficient and of the stream Mach number. Tables and corresponding graphs are included to illustrate numerically the theoretical results derived. For example, it is found that, for an elliptic profile of thickness coefficient 0.15 and a stream Mach number 0.80, the center of pressure moves rearward a distance 2.6 percent of the chord from its position in the incompressible flow.
- Fluid Mechanics