Evaluation of Closure Hypotheses Using Recent Experimental Data on the Similarity Region of Swirling Jet Flow
Paper in proceedings, 2007
An experimental recent study by Shiri et al. using laser Doppler anemometry showed that the growth rate enhancement due to swirl (c.f.\ Gilchrist, Naughton) does not persist in the far-field of a swirling jet flow with moderate swirl numbers (0.15 and 0.25). The results were consistent with the equilibrium similarity theory of Ewing in which the mean swirl velocity was argued to decrease downstream as $1/(x-x_o)^2$, while the mean stream-wise velocity decreased as $1/(x-x_o)$. The investigation included all three velocity components of the turbulence quantities at a swirl number of $S=0.25$, and all moments to third order were obtained (except those involving both the azimuthal and radial components simultaneously). As noted by George, if there were an effect of the source conditions on the similarity profiles, it is in the second and higher moment profiles where it would be expected to appear. The second and third-order moments are quite close to the earlier non-swirling results; some are collapsing perfectly, others have a slight difference. Regardless, the results are of considerable interest, since many of the quantities measured are those which must be modeled in all second-order closure models. This evaluation is of particular interest since both the mean azimuthal and mean radial velocities were obtained directly, meaning that both continuity and momentum balances were possible. The primary goal of this paper was originally to carry out such evaluations, but that work is still in progress. Here the swirl is shown to have a negligible effect on the overall Reynolds normal and shear stress balances.
Laser Doppler Anemometry