PIV on the surface

Abstract

New approach to surface flow visualization based on combination of oil film method with PIV approach is presented. Oil film is seeded with optically contrast particles and two or more images of these contrast particles are acquired at some time interval at desirable flow parameters. Cross-correlation analysis of these images allows to determine parameters of oil film movement and, as a result, to restore surface flow parameters. Surface streamlines can be restored correctly since the directions of oil shift vectors are coincident with the direction of surface streamlines. Shear stress distribution can be visualized since the magnitudes of oil shift vectors are proportional to shear stress value. Since oil film is moved along the model surface the restoration of surface streamlines is completely correct. Specific feature of presented method is that the model can move between acquisition of images, so this model movement should be determined and subtracted from particles movement to get the correct surface flow parameters. Since only small shift of oil film is analyzed, multiple tests with different airflow parameters can be made using single model preparation. Since oil viscosity can be varied within a wide range and can be fitted to expected shear stress value, different flow types ranging from low-speed to high-speed can be studied using this method.