- Award ID(s):
- 1905252
- NSF-PAR ID:
- 10214067
- Date Published:
- Journal Name:
- ASME 2020 Conference on Smart Materials, Adaptive Structures and Intelligent Systems
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Large-eddy simulations (LES) over a NACA0018 airfoil at a low Reynolds number (Re = 50, 000) fluid flow are performed to investigate the effect of active flow control at different angles of attack (AOA = 10 to 20 degrees) using low amplitude surface morphing backward (opposite to the airfoil’s forward motion) traveling wave actuation on the suction (upper) side of the airfoil. The curvilinear immersed boundary (CURVIB) method is used to handle the moving surface of the airfoil. While our previous simulations indicated the effectiveness of traveling waves at near stall angle of attack (AOA = 15 degrees), the effectiveness of these waves at post-stall AOA such as AOA = 20 degrees is not understood. The actuation amplitude of the surface morphing traveling waves is a* = 0.001 (a* = a/L, a: amplitude, L: chord length of the airfoil), and the range of the reduced frequency (f* = fL/U, f: frequency, U: free stream velocity) is from f* = 4 to 16. The results of the simulations at the post-stall angle of attack (AOA = 20 degrees) show that the lift coefficient, CL, increases by about 23%, and the drag coefficient, CD, decreases by about 54% within the frequency range from f* = 8 to f* = 10.more » « less
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The main two mechanisms of morphing wall flow control are direct injection of momentum in the streamwise direction and indirect momentum transfer via triggering instabilities. Traveling waves have been shown to perform better than standing waves, probably because they can use both mechanisms. However, the relative importance of the two mechanisms is not known. To differentiate between the mechanisms, a range of parameters (frequency, amplitude, and starting location) at stall (15 deg angle of attack) and poststall (20 deg angle of attack) is tested using wall-resolved large-eddy simulations with a sharp-interface curvilinear immersed boundary method at a low Reynolds number of [Formula: see text] over a NACA0018 airfoil. The results of the simulations demonstrate that the flow is reattached within a range of nondimensional frequencies, actuation amplitudes, and starting locations of oscillation at the stall and poststall angles of attack. Significant lift enhancement and drag reduction are also observed within these ranges. The nondimensional frequency range at which the flow is reattached is found to be similar to the dominant nondimensional frequencies of leading-edge vortex shedding of the unactuated airfoil. These indicate that the indirect transfer of momentum is the dominant mechanism because direct injection of momentum increases with the increase of amplitude and frequency; that is, separation should reduce as they increase. Nevertheless, direct injection of momentum improves the performance relative to pure excitations of standing waves when instabilities are triggered.
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