Oscillation and heat transfer in upward laminar impinging jet flows

Upward, laminar, axisymmetric, pipe-issued, submerged impinging jets, with the water as the working fluid, are numerically investigated. The impingement surface is subjected to heating, which causes the wall jet to prematurely separate from the impingement surface and turns the following region into a dead zone where the heat transfer rate deteriorates. Effects of (1) the inlet-based Reynolds number, (2) the heating-rate dependent Grashof number, and (3) the impingement-surface height to the inlet-diameter ratio are examined in detail. It is found that the separated jet oscillates when the Richardson number of the flow is moderate, but it separates without any oscillation when the Richardson number is large. The flow oscillation also induces cyclic fluctuations in on-surface quantities, such as, the Nusselt number, the surface temperature, and the skin-friction coefficient. The flows slowly approach to statistically steady states where oscillation parameters and heat transfer properties tend to stabilize about fixed values.