Development and implementation of novel flow control techniques for nonslender delta wings

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2017
Çelik, Alper
Understanding and controlling the physical phenomenon behind the aerodynamics of low to moderate swept delta wings has been a challenge for researchers during the last few decades, which is stimulated by their widespread use in unmanned combat air vehicles (UCAVs) and micro air vehicles (MAVs). Although delta wings are capable of generating high lift and stable flight performance at high angle of attack, the problems related to lack of conventional flow control surfaces compel the researchers to explore new means of flow control techniques on delta wings. In the current study, it is aimed to control the flow structure of low swept delta wing with sweep angle of Λ=45o using novel passive flow control techniques. The experiments are conducted in a low speed wind tunnel using the techniques of laser-illuminated flow visualization, surface pressure measurements, and particle image velocimetry (PIV). Three different passive flow control methods are developed and investigated including bioinspired edge modification, bioinspired material modification, and passive bleeding, where the details of each are described in the paragraphs below. Bioinspired edge modifications are studied based on similarities between delta wing shapes and cetacean flukes. Reynolds number is varied within the range of 104 < {u1D445}{u1D452} < 2.5×104 and the attack angles are 4 ≤ {u1D6FC} ≤ 12. The results indicate that the edge modification deteriorates the flow structures compared to the base wing planform within the operational range tested in the current study. Passive bleeding, using the inherent pressure difference between the suction and pressure side of the wing, is studied to investigate its effect on the flow structure of a 45 deg swept delta wing. Three different bleeding configurations are tested to identify the effectiveness of the control technique for a broad range of attack angles 6 ≤ {u1D6FC} ≤ 16 deg at Reynolds numbers 104 < {u1D445}{u1D452} < 105. The results indicate that all bleeding configurations alter the flow field over the planform, where a proper bleeding induces significant improvement on the overall flow pattern. At sufficiently high angle of attack the recovery of the vortical structures with significant increases in the magnitude of suction pressure coefficient −{u1D436}{u1D45D}, which implies the elimination of three-dimensional surface separation is achieved. On the contrary, at low attack angles, the bleeding causes reduction in the magnitudes of suction pressure coefficient −{u1D436}{u1D45D} in general, indicating a loss in suction performance of the planform. The bioinspired material modification study is based on flexion ratio concept inspired from animal propulsion. For this purpose, the experiments are conducted for a broad range of Reynolds numbers 104 ≤ {u1D445}{u1D452} ≤ 105 and attack angles 8 ≤ {u1D6FC} ≤ 30 deg using four different 45 deg swept delta wings of flexion ratios a/S = 0.3, 0.5, and 0.7 along with a base planform. The results indicate that the partial flexibility of the delta wing does not induce notable variation in the flow structure over the wing within the Reynolds number ranges tested in the current study.
Citation Formats
A. Çelik, “Development and implementation of novel flow control techniques for nonslender delta wings,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.