An experimental study of the relationship between forces and moments and vortex breakdown on a pitching delta wing
Soltani, Mohammad Reza
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https://hdl.handle.net/2142/22695
Description
Title
An experimental study of the relationship between forces and moments and vortex breakdown on a pitching delta wing
Author(s)
Soltani, Mohammad Reza
Issue Date
1992
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
Language
eng
Abstract
Wind-tunnel experiments were performed to study the complex flow mechanisms on a 70-deg. sharp leading-edge delta wing model at both static and dynamic conditions at a Reynolds number of 1.43 $\times$ 10$\sp6$. Large amplitude oscillatory motions were produced by sinusoidally pitching the model over a range of reduced frequencies. Ramp motions were obtained using an initial sinusoidal increase in angle of attack and hold. Aerodynamic forces and moments were obtained from a six-component internal strain-gauge balance. In addition, smoke flow visualization was conducted to study the development, and breakdown of the leading-edge vortices under static, dynamic, and ramp conditions. The visualization experiment was performed at a Reynolds number of 0.16 $\times$ 10$\sp6$.
Static forces compared well with previously published data. The non-linear vortex lift and the movement of the burst point over the wing surface were related to changes in the measured lift-curve slope. Asymmetrical bursting produced by testing the model at nonzero sideslip angle, had a significant influence on the magnitude of the measured forces and moments.
Dynamic data varied substantially with reduced frequency. Large forces and moments overshoots, a delay in dynamic stall, and a hysteresis loop between the values of aerodynamic loads in upstroke and downstroke motion were observed. The dynamic vortex breakdown point was seen to reach the trailing-edge at a smaller angle of attack than it did when in the static case. However, at large angles of attack, its position lagged that of the static model. The magnitude of the rolling moment coefficient was strongly influenced by the reduced frequency.
For the ramp motion case, aerodynamic forces and moments closely followed those of the oscillatory case during the pitch-up motion. However, upon cessation of the motion, the persistence of the dynamic effects was a strong function of the pitch rate. Terminating the motion at 24 deg. angle of attack produced lower lift and normal force values when the data were compared to their static values. This was caused by the early bursting phenomenon observed during the dynamic motion, thus reducing dynamic lift and normal force coefficients.
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