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Numerical investigation of thickness-to-chord ratio on aerodynamic characteristics and flow field of a low swept delta wing

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2019
Cesur, İsmail Sadi
Recent years revealed the increased interest in Unmanned Combat Air Vehicles (UCAVs) and Unmanned Air Vehicles (UAVs) which utilize delta wing planforms, making the Delta wing studies more prominent. Delta wings are characterized by two counter-rotating vortices on leading edges formed by the detached shear layer from the windward side of the planform. Those vortical structures lower the pressures on the suction side of the wing therefore contributes to the increase of the lifting and maneuvering capacity of the wing. Present study, involving Computational Fluid Dynamics (CFD) simulations, investigates the effects of the thickness-to-chord ratio of a low swept delta wing on the aerodynamic characteristics and the flow field. In the present study, a delta wing planform having a 35 degrees of sweep angle with two thickness-to-chord ratios are numerically examined at Reynolds Numbers, RE = 35000 & 300000 and angles of attack ranging from 4° to 40°. A mesh independence study is conducted and CFD results are validated by the data of an experimental study. SST k-ω turbulence model with the extension of curvature correction function is utilized due to its success of yielding the most accurate results. When flow field results are investigated it is seen that the vortex breakdown phenomena and three-dimensional flow separation occur much sooner with the increase of both thickness-to-chord ratio and Reynolds number, such that in some cases steady vortex structure breaks down right at the apex of the wing. The results also indicate that thickness-to-chord ratio has a significant effect on the aerodynamic coefficients and the flow field, such that, with the increase in t/c ratio drag coefficient, CD increases at all angles of attack, ratio of the lift and drag coefficients, CL/CD decreases. Moreover, CL and Cm values are decreasing with the increase of t/c ratio with the exception for the region till the stall angle of attack is reached. Post stall values of CL and Cm are higher for the thin wing. With the increase in the Reynolds number, all aerodynamic coefficients are increased when it is compared to the lower Reynolds Number results. However, individual trend of the aerodynamic coefficients mentioned above remains the same. To conclude, the aerodynamic coefficients and flow field are highly affected by the thickness-to-chord ratio, which in turn might prove to be a useful tool to control the flow field, and a step to improve the numerical calculation methods to acquire the vortical structures.