Investigation of Unsteady Boundary Layer Induced by Propagating Compression Wave : 1st Report, Experiment Using Laser Differential Interferometry

Abstract

The unsteady boundary layer induced by propagating compression wave has been investigated by means of a recently developed laser differential interferometry (LDI) method using Wollaston prisms. The difference of the two detector signals in LDI will therefore be essentially free of vibrations and laser output variations. LDI can be made more sensitive to optical path changes by 2 to 3 orders of magnitude than in classical interferometry. The sensitivity was sufficiently high to record the density variations by compression waves. The measurements of the time-dependent profiles gave detailed information on the process of formation of the unsteady boundary layer induced by propagating compression wave in a constant-area duct. It was found that the laminar-to-turbulent transition in unsteady boundary layer flow, which describes the density profiles at a strength of the initial compression wave from 9 kPa, exists.