Boundary-layer separation control using laser-induced air breakdown
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abstract
Modification of the flow separation characteristics of a laminar airfoil using a remotely located high-power laser was experimentally investigated in a low-speed, low-turbulence wind tunnel. A laminar airfoil model (chord length of 500 mm) was designed and fabricated to emulate the flight characteristics of a small aircraft. At 0 deg angle of attack, the airfoil model was determined to have an incipient laminar separation bubble on its lifting surface between 67 and 80% chord. A strong laser-induced breakdown was generated 2 mm upstream of the leading edge by focusing a collimated beam emitted from a 900 mW laser at 1064 nm through a convex lens. The high-temperature plasma generates a shock wave and a cell of heated air that travels along the airfoil lifting surface and interacts with the boundary-layer flow. Two-component particle image velocimetry was used to map the transient and steady-state flow. The hot, low-density fluid induced significant exchange of momentum between the freestream and the incipient separation zone, leading to reattached flow for a period lasting seven orders of magnitude longer than the plasma lifetime. These results show promise that laser-based energy-deposition approaches can be used for effective flow-control applications.
