Feature Correlation Velocimetry for Measuring Instantaneous Liquid Sheet Velocity

Abstract

We describe a novel nonintrusive velocimetry technique for measuring the instantaneous velocity field on a liquid sheet. Short wavelength corrugations are naturally formed on the surface of a liquid sheet when the sheet interacts with ambient air. This method, called feature correlation velocimetry (FCV), relies on cross-correlation of such short wavelength corrugations visualized on the liquid sheet surface when captured using a high-speed camera. An experimental setup was created for producing a liquid sheet of known thickness and velocity. After imaging the liquid sheet with a high-speed camera, cross-correlation was employed at various spatial locations on the liquid sheet. To examine the fidelity of the method, laser Doppler velocimetry (LDV) measurements were obtained for a range of flow rates at the same spatial locations and were compared with the FCV values. The FCV values were found to be consistently within 7% of the LDV readings with the FCV measurements being consistently less than those from the LDV. In order to examine the cause of the bias error, a theoretical model of the liquid sheet has been developed. Based on the model predictions, the bias error was observed to scale as U3/2, where U is the local instantaneous liquid sheet velocity. After correcting for this bias error, a good match was observed between the FCV and the LDV readings. As an application of the FCV method, the near-nozzle region of an annular sheet exiting a spray injector has been characterized.

Estimating velocity in Gasoline Direct Injection sprays using statistical pattern imaging velocimetry

“…Statistical pattern imaging velocimetry (SPIV) can be used to extract the near-field particle velocities in transient sprays from high-speed videos. 20–24 SPIV is similar to ICV in that it is based on estimating the time correlation between the two spatial points with ensemble of samples to find the displacement. ICV is typically used to extract the mean velocity field which is an essential physical property for most of the applications.…”