Heat transfer and flow visualization of swirling impinging jet on flat surface using helicoid inserts

Abstract

The heat transfer and flow structure of swirling impinging jet on a flat surface with helicoid inserts are experimentally and numerically analyzed. The study is focused on flow dynamics intended to describe the influence of swirl on the mechanics of impingement by varying the number of helicoid surfaces named as single, double, and triple helicoid inserts. A helicoid surface may be considered as having an infinite number of adjacent helical curves that rotates symmetrically about Z axis. The thermochromic liquid sheet and oil film technique are used to visualize the heat transfer characteristics and flow structure on the impinging surface, respectively. The numerical analysis is carried out for Swirl number Sw = 0.75 and Reynolds number value of 23,000 and for jet exit to impinging surface distance of H/D = 1, 2, 3, 4 using CFD. The flow characteristics of swirling jet are also compared with circular impinging jet. The flow characteristics are presented in terms of axial velocity variation and the distribution of vorticity and velocity vectors are also visualized. In addition turbulent statistics are also presented. The axial component of velocity of jet leaving triple helicoid at the stagnation region is relatively lower than single and double helicoids due to the presence of axial recirculation zones and the tangential velocity component of triple helicoid is higher in the region which corresponds to radial distance r/D = 0–0.4, 0–0.8, and 0–1.4 at H/D = 1, 2, and 3, respectively, compared with single and double helicoids. The axial velocity component exhibits flat profile for the single and double helicoids at increased H/D distances (H/D = 4). The vorticity distribution is relatively more intense for triple helicoid at the downstream of jet near the wall jet region causing it to entrain more ambient air compared with single and double helicoids.