Concentration profiles in shallow turbulent wakes

The present study deals with the noninvasive measurement of concentration i n the intermediate shallow turbulent wake region using a video-imaging tech nique. The pow depths considered in the present study are small compared to the width of the channel and the generated wakes are categorized as shallo w. On the basis of the observed behavior. the wakes are classified as deep- shallow wakes and shallow-shallow wakes. The topology of the dye concentrat ion distribution in the near and intermediate wake region indicates that th e vortex structure tends to be preserved when the flow depth is relatively high a,ld the dominant eddy structures are similar to that noticed in conve ntional two-dimensional,wakes. In shallow-shallow wakes, the conventional K arman vortex street appears to be annihilated or intermittent. The lateral concentration distribution at several axial stations covering the first thi rty body widths are considered for analysis. The instantaneous concentratio ns are observed to be several times higher than the corresponding mean valu es. Attempts are also made to determine the paths traversed by the vortex c ores and the vortex, core convection velocity. The axial variation of the w ake half-width with depth of bow is also examined. A model is developed to predict the spread of the wake with downstream distance fr-oil the test bod y. A friction length scale is introduced in the model to account for the ir influence of depth and bed friction on the development of the wake.