Control of Flow Past a Wing Section with Plasma-based Body Forces
AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH AIR VEHICLES DIR/ AERONAUTICAL SCIENCES DIV/COMPUTATIONAL SCIENCES BRANCH
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The response of the flow past a stalled NACA 0015 airfoil at 15 deg angle of attack and Reynolds number of 45, 000 to body forces originating from radio-frequency asymmetric dielectric-barrier-discharge actuators is described via direct numerical simulations. The theoretical model couples a phenomenologically derived averaged body force with a high-order 3-D compressible Navier-Stokes solver. The body force distribution is assumed to vary linearly, diminishing away from the surface until the critical electric field limit is reached. Various magnitudes and orientations of the force field are explored, ranging from vertically upwards away from the body to vertically downwards towards the body. The imposed body forces couple to the non-linear inertial terms and the pressure gradients to engender a complex sequence of events. A significant streamwise component assures the reduction or elimination of stall with the formation of a stable wall-jet. When the only component of the force vector is pointed normal to and away from the surface, no control effect is achieved. On the other hand, when the force vector is directed towards the surface, a shallower separation region is observed, accompanied by unsteady boundary layer development. At the low Mach number considered 0.1, the work done by the force has little impact on the solution, and density variations remain less than 5. Relaxation effects are explored by abruptly switching off the force, and estimates of response times are noted. The lack of a proper spanwise breakdown mechanism for the separated shear layer in 2-D simulations results in large coherent structures, whose response in transient and unsteady asymptotic states differ significantly from those observed in 3-D. Nonetheless, if the force is sufficiently effective to eliminate separation, the flowfield becomes generally two-dimensional and steady in the vicinity of the airfoil, and the overall results from 2-D and 3-D analyses yield similar results.
- Operations Research
- Fluid Mechanics