Direct numerical simulation for laminarization of turbulent forced gas flows in circular tubes with strong heating

Abstract

The direct numerical simulation (DNS) of turbulent transport for a gas with variable properties has been conducted to grasp and understand the laminarization phenomena caused by strong heating. In this study, the inlet Reynolds number based on a bulk velocity and pipe diameter was taken as Re =4300 as in the experiments by Shehata and McEligot (1998) . The measured wall temperature distribution was applied as a thermal boundary condition. The number of computational nodes used in the heated region was 768×64×128 in the z -, r - and φ -directions, respectively. Turbulent quantities, such as the mean flow, temperature fluctuations, turbulent stresses and the turbulent statistics, were obtained via DNS. Predicted mean velocity and temperature distributions and integral parameters agreed well with the experiments. The Reynolds shear stress, indicating turbulent transport of momentum, decreases along the streamwise direction. The cause of this reduction can be considered to be that the fluid behavior changes drastically in the near wall region due to strong heating which induces significant variations of the gas properties and, in turn, acceleration and buoyancy effects. In a visualization of the results, one sees that the vortical structures are primarily suppressed within the first section of the heated region ( z / D =0–5) and are not regenerated further downstream.