Two and three component velocity measurements in a wind tunnel using PIV

This paper describes the development of particle image velocimetry (PIV) to measure instantaneous spatial distributions of velocity in flows generated around models in a low speed wind tunnel with a test section 3m wide by 1. 5m high. The difficulties associated with using PIV in air at this scale, a nd how they can be overcome, are discussed. Stereoscopic PIV is used to cor rect errors due to parallax that are present in velocity components measure d in the plane of a light sheet when there is an accompanying flow through the sheet. This technique is also used to measure all three components of v elocity in planes across a flow. It is found that apparently good estimates of a mean flow field can be obtained by averaging as few as ten instantane ous measurements of the flow field. The flows studied are generated by a 1/ 8 scale model of an aircraft for which the wing sweep can be varied. Measur ements of velocities associated with the main vortex structures generated o ver the wing are presented for a sweep angle of 70 degrees. Measurements of velocities recorded in the wake of a large fuel tank mounted below the win g, for a wing sweep of 45 degrees, are also shown.