Measurement of separating flow structures using a multiple-cameraDPIV system

摘要

A novel multiple-camera system for the recording of digitalparticle image velocimetry (DPIV) images acquired in a two-dimensionalseparating/reattaching flow is described. The measurements wereperformed in the NASA Langley Subsonic Basic Research Tunnel as part ofan overall series of experiments involving the simultaneous acquisitionof dynamic surface pressures and off-body velocities. The DPIV systemutilized two frequency-doubled Nd:YAG lasers to generate two coplanar,orthogonally-polarized light sheets directed upstream along thehorizontal centerline of the test model. A recording system containingtwo pairs of matched high resolution, 8-bit cameras was used to separateand capture images of illuminated tracer particles embedded in the flowfield. Background image subtraction was used to reduce undesirable flarelight emanating from the surface of the model, and custom pixelalignment algorithms were employed to provide accurate registrationamong the various cameras. Spatial cross correlation analysis withmedian filter validation was used to determine the instantaneousvelocity structure in the separating/reattaching flow region illuminatedby the laser light sheets. In operation the DPIV system exhibited a goodability to resolve largescale separated flow structures with acceptableaccuracy over the extended field of view of the cameras. The recordingsystem design provided., enhanced performance versus traditional DPIVsystems by allowing a variety of standard and non-standard cameras to beeasily incorporated into the system