Aerodynamics of a chined forebody oscillating in pitch
Mange, Richard Lewis
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https://hdl.handle.net/2142/21683
Description
Title
Aerodynamics of a chined forebody oscillating in pitch
Author(s)
Mange, Richard Lewis
Issue Date
1996
Doctoral Committee Chair(s)
Bragg, Michael B.
Department of Study
Aerospace Engineering
Discipline
Aerospace Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Aerospace
Engineering, Mechanical
Language
eng
Abstract
A low-speed experimental study of the effects of an oscillatory pitching motion on the flowfield of a chined forebody has been performed. These tests were conducted in the University of Illinois low-speed (0-240 ft/sec), low-turbulence ($<$0.1%), 3 by 4 ft, open circuit wind tunnel. The high fidelity, NC machined aluminum model was sting mounted and oscillated sinusoidally in pitch from 0$\sp\circ$ to 52$\sp\circ$ angle of attack without sideslip. The effects of reduced frequency as well as free-stream Reynolds number were investigated by running a range of tunnel velocity/model oscillation frequency combinations. Reynolds numbers, based on the 3-inch base diameter of the forebody, of 1.4 x 10$\sp5$ to 2.8 x 10$\sp5$ were tested. The experiments cover a range of oscillation frequencies from 0 to 1 Hz, corresponding to reduced frequencies, based on the 10.5-inch length, of 0 to 0.0275. Surface pressures were measured at all conditions using an array of 91 static pressure taps. Normal force and pitching moment were determined by integrating these data. Surface oil and smoke flow visualization were utilized to determine the vortex system and help interpret the surface pressure data.
Steady flow visualization revealed the importance of secondary boundary-layer separation on the leeward surface of the chined forebody. This separation was caused by a steep spanwise surface pressure gradient between the chine edge and the suction pressure peak associated with the primary vortex. Surface static pressure data indicated a hysteresis effect in the unsteady flowfield. Leeward surface static suction pressures built-up at lower angles-of-attack in the dynamic upstroke than in the steady case. The opposite was true in the dynamic downstroke. This hysteresis in leeward surface static pressures also resulted in a hysteresis in secondary boundary-layer separation, secondary vortex formation and the integrated forces and moments. These data showed increased lift in the upstroke and decreased lift in the downstroke, with negligible effects on the center-of-pressure.
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