Higher-order moments of velocity fluctuations in the wake of a short stack

Abstract

The effect of jet velocity relative to the crossflow velocity on the higher-order moments of velocity fluctuations characteristics in the wake of stack is reported in this study. The cross-flow Reynolds number was ReD = 2.3×104 and the jet-to-cross-flow velocity ratio was varied from R = 0 to 3. The stack was partially immersed in a flat-plate turbulent boundary layer, with a boundary layer thickness-to-stack-height ratio of δ/H = 0.5 at the location of the stack. The skewness factor, flatness factor and triple correlations are found to be influenced by the flow regime. The deviation of skewness and flatness factors from the Gaussian fluctuation values of zero and 3 are more pronounced outside the wake centre region due to the presence of the separated shear layers and vortex structures. The high values of the skewness and flatness factors for all values of velocity ratio within the vicinity of the stack free end are related to the tip vortex structures near the stack free end which decrease in strength as the value of R increases. In addition, the separated shear layers from both sides of the stack contribute to the high values observed away from the wake centreline.