Interferometric Measurements in a Turbine Cascade Using Image-Plane Holography

Abstract

A holographic technique used to produce image plane interferograms with white light reconstruction is described. This was used to study the transonic flow in a passage of a turbine stator cascade at a typical Reynolds number, Mach number, and free stream to blade surface temperature ratio. Both absolute holographic interferograms (fringes of constant flow density) and differential holographic interferograms (changes of density in 100 μsecs) are presented showing fine details in the boundary layer flow, trailing edge shocks, and wake structure. By counting the fringes on the interferograms, the free stream and surface Mach numbers and boundary layer temperature gradients can be determined.