Density Field Measurement of Thermal Convection at High Rayliegh Number Coupling with Sound Field by Digital Speckle Photography

Laser speckle photography is a well-established optical method which can be applied to quantitative measurements of density fields of fluid flows in wide dynamic range. This method is extended to efficient digital method based on cross-correlation processing, called digital laser speckle photography. The digital images of laser speckle pattern are acquired by PC, and the same algorithm with cross-correlation PIV can be applied to reconstruct the local density gradient vector. In this investigation, the method is applied to density field analyses of a thermal convection constrained by coupling with an acoustic standing wave induced in a horizontal closed duct.