Flow Mechanism of λ-type Pseudoshock Waves in a Straight-Square Duct

Abstract

This paper is concerned with the internal structure of λ-type pseudoshock waves in a straight-square duct. The experiments were carried out for M₁=1.77, where M₁ Was the flow Mach number just ahead of the pseudoshock wave, using a two-component, dual-beam laser Doppler velocimeter (LDV) and double exposure laser holographic interferograms. The velocity distributions in the pseudoshock wave were measured in detail. The variations of velocity and boundary layers displacement thickness were clarified. Especially, the displacement thickness increased at the shock wave locations and decreased in the regions between the shock waves. The velocity distributions calculated by the density distributions, which were measured by using the holographic technique, were compared with the results from LDV. It was found that the central flow in the pseudoshock wave was closely related to the isentropic flow, while the flow near the wall was closely related to the adiabatic flow.