Direct numerical simulation of thermal turbulence in an aero-engine blade channel

Abstract

The flow and heat-transfer phenomena are simulated by direct numerical simulation in the NACA65 blade channel with a Reynolds number equaling to 1.367×105. Induced by the strong adverse pressure gradient, the flow separations are observed on the suction surface with the multi-scale and multi-layer vortices. The DNS results indicates that the backflow transition is triggered by the small-scale spanwise-vortex fluctuations due to the viscous linear instability, and thereafter is further stretched into the quasi-streamwise vortices due to the upper K-H rolls, which generates the typical coherent structures in the flow-separation region. The Reynolds shear stresses and turbulent heat flux are found very strongly and actively concentrating in the region bounded by the blade-wall and the upper boundary of separation where the variety of ejections and sweeps are observed. These ejections and sweeps promote the momentum and heat transfers, which results in the large temperature gradients in both the near-wall and flow-separation regions. Moreover, the separation and reattachment zones present the non-similarity distributions for both the wall-normal heat flux and Reynold shear stresses due to the strong adverse pressure gradient. Therefore, the diverse profiles of velocity and temperature can be found developing in streamwise along the suction surface. However, through applying the newly-developed wall-bounded law formulations, it is demonstrated that these wall-laws are even universally capable of accurately representing these diverse velocity and temperature profiles.