A PHASE-LOCKED HIGH-SPEED REAL-TIME INTERFEROMETRY SYSTEM FOR LARGE-AMPLITUDE UNSTEADY FLOWS

A high-speed phase-locked interferometry system has been designed and developed for real-time measurements of dynamic stall flow over a pitc hing airfoil. Point diffraction interferograms of incipient flow separ ation over a sinusoidally oscillating airfoil have been obtained at fr aming rates of up to 20 kHz and for free stream Mach numbers of 0.3 an d 0.45. The images were recorded on 35 mm ASA 125 and ASA 400 films us ing a drum camera. Special electronic timing and synchronizing circuit s were developed to trigger the laser light source from the camera and to initiate acquisition of the interferogram sequence from any desire d phase angle of oscillation. The airfoil instantaneous angle of attac k data provided by an optical encoder was recorded via a FIFO data buf fer into a microcomputer. The interferograms have been analyzed using software developed in-house to get quantitative flow density and press ure distributions.