An experimental study on the flow characteristics of a three-dimensional turbulent wall jet in a limited space

To examine the effect of a vertical plate positioned in front of a rectangular orifice on the time-averaged flow characteristics of a three-dimensional turbulent wall jet,we measured three important quantities: U velocity profiles,velocity half-width,and maximum velocity decay rate with various Reynolds numbers and submerged depths by using particle image velocimetry (PIV). The jet flow field was found to be divided into three major decay regions in terms of the maximum velocity decay exponents:a natural three-dimensional turbulent wall jet region (region I),a vertical plate affecting region (region II),and a near-wall region (region III). In region II,the focus of the present study,the variations in the three measured quantities with downstream distance were found to be independent of the Reynolds number. Compared with the natural wall jet,the confined jet developed substantially faster,and the spread rates in both the longitudinal and lateral directions were significantly higher,owing to the presence of the vertical plate. The spread rate in the symmetry plane was 0.043 within the range of H—1.75H. The lateral spread rate was slightly sensitive to a water depth interval of 0.5H,and the growth rate correspondingly increased from 0.205 to 0.270. Furthermore,the maximum velocity decayed dramatically in this region,with an exponent value of 1.095,and was independent of water depth. The flow characteristics of region II,compared with the natural case,were similar to those in the radial decay region. Therefore,the flow field in region II appears to have fully developed and entered into the radial decay region in advance.