Effect of initial conditions on mean flow characteristics of a three dimensional turbulent wall jet

The effect of initial conditions in a 200 mm x 1000 mm x 400 mm sidewall enclosure on the mean flow characteristics of a three dimensional turbulent square wall jet has been studied experimentally. The initial conditions are varied by varying the length of the nozzle; it is varied as l/h = 10, 50, and 90, where l and h indicates the nozzle length and the side of the square nozzle, respectively. The effect of nozzle length on initial velocity profiles, velocity distribution in lateral and wall normal directions, spread rate, decay of maximum mean velocity, local Reynolds number and similarity behaviour has been studied. The wall normal spread width is higher for the nozzle length l/h = 10 in the near field (x/h <= 10) but this trend completely changed after x/h >= 10. The spread rate is found independent of the initial condition of the nozzles in the fully developed region. The decay rate of maximum mean velocity is found higher for l/h = 10 in the region of (5 <= x/h <= 25), whereas decay rate becomes independent of the initial conditions in the fully developed region (x/h >= 25). The local Reynolds number variation is also estimated along the downstream directions for present case and found that the local Reynolds number (Re-x) reaches approximately 56% of the jet exit Reynolds number (Rejet) at x/h=40 for nozzle length l/h = 10, while it is 57% and 59% of Re-jet for the nozzles l/h=50 and l/h=90 respectively at the same location. The nozzle l/h = 10 attained self similar behaviour more quickly as compared to the other nozzles. The sidewall played a significant role which pushed the fluid more towards the center resulting in a lower jet half width in the wall normal direction as compared to the corresponding case, without a sidewall. The decay rates of the maximum mean velocity for all the nozzles are estimated to be 1.08 which is in the accepted range found in the literature.