1 Supersonic Drag Reduction with Repetitive Laser Pulses through a Blunt Body

A drag over a flat-nosed cylinder with repetitive laser pulse irradiations ahead of it were experimentally measured in a Mach-1.92, in-draft wind tunnel. Laser pulses were focused using a plane-convex lens fabricated on the nose of the cylinder at a repetition frequency of up to 10 kHz and power of 70 W at a maximum. The drag was measured using a low-friction piston which was backed by a load cell in a cavity at a controlled pressure. Under the experimentally available operation conditions, an up-to-3 % drag reduction and an efficiency of energy deposition of about 10 were obtained. Mechanisms of the drag reduction are analyzed based on experimental flow visualization and numerical simulation. Nomenclature A = cross-sectional area of cylinder model c = constant D = drag D0 = drag without energy deposition E = laser energy per pulse FL = force to/from load cell FO = resultant force from O-rings f = laser pulse repetition frequency l = distance between cylinder nose and laser focus P = static pressure P0 = atmospheric pressure Psub = static pressure in sub-chamber t = time originated in (first) laser pulse iradiation U0 = test flow speed VL = output voltage of load cell VL,O = output voltage of load cell during wind tunnel run without laser energy depositions VL,W = output voltage of load cell during wind tunnel run with laser energy depositions W = time-averaged laser power = fE D = constant determined in calibration E = constant determined in calibration 'D = decrement in drag due to energy depositions K = efficiency of energy deposition I