Development of the Focused Malley Probe as a Local Aero-Optical Measurement Technique

Abstract

A novel local aero-optical measurement technique, termed the focused Malley probe, is presented, where two converging-diverging laser beams passing through a wind tunnel are used to perform localized aero-optical jitter and convective speed measurements. Validating experiments were conducted using a subsonic speed tunnel with a small diameter cylinder placed in the middle of the test section to create local aero-optical distortions in the wake downstream. Measurements were performed in the wake downstream of the cylinder, in the freestream upstream of the cylinder, and in the turbulent boundary layer upstream of the cylinder. Spectral analysis of the cross-correlations between two beams in these preliminary experiments clearly demonstrate the ability of the focused Malley probe under certain conditions to measure convective velocity primarily near the focal point. In the case when the focal points were placed inside the cylinder’s wake, a spectral peak corresponding to the shedding frequency was clearly resolved despite the presence of the corrupting effects from the boundary layers at the walls of the tunnel. Various experimental and data processing requirements to obtain accurate results are also discussed.