Evaluation of PISFV Method in Subsonic Wind Tunnel

Abstract

Particle image surface flow visualization (PISFV) method was proposed recently. The idea of the method is to measure some small shift of an oil film applied on the investigated object surface and to restore the complete pattern of surface flow numerically. Optically contrast (luminescent) hard particles are added to the oil film and at least two images of the particledistribution on the model surface are acquired at some time interval in the flow by a CCD camera. Processing of such images using cross-correlation analysis (similarly to PIV method) provides the determination of particle displacement vectors. Possible model shift on the images should be subtracted from particle displacement to obtain oil shift vectors. The direction of oil shift coincides with the direction of the surface streamlines. That allows to reconstruct these streamlines. The shear stress field can be calculated from oil shift magnitude if oil film thickness is known. Even the small oil shift for a few pixels of image is sufficient for surface flow visualization. Oil redistribution on investigated surface is insignificant and several flow regimes can be studied using one oil film application.