Two-axes Scheimpflugfocusing for particle image velocimetry

Abstract

The objective of this work is to demonstrate the capabilities ofa two-axes, three-dimensional particle image velocimetry (PIV)system for future use as a large-scale wind tunnel researchtool. A two-axes PIV system provides the capability for cameraplacement virtually anywhere within three-dimensional spacerelative to the laser sheet plane of measurement. TheScheimpflug focusing method is applied in two orthogonal axesto achieve off-axis focusing. The two-axes, three-dimensionalPIV system uses off-axis stereoscopic viewing to determine twoperspective measurements of a three-dimensional velocity fieldwithin the laser sheet. A unique calibration procedure is usedto determine the optical parameters that describe the positionof the camera systems and which are necessary to perform thethree-dimensional reconstruction of the displacements. This paper presents the calibration procedure as well as a method forreconstructing the three-dimensional particle displacements forthis two-axes, three-dimensional PIV system. This two-axes,three-dimensional PIV system was demonstrated by measuringthree-dimensional displacements of a target. Maximuminstantaneous errors are estimated as 2% or less for all velocity components. These error estimates are for instantaneousdisplacements and include all error sources. The two-axes,three-dimensional PIV system was also used to make measurementsof the freestream velocity within a wind tunnel. Theout-of-plane freestream component of velocity measured by thePIV system differed from the expected value by less than 1.1{%}.