Large eddy simulation of turbulent flow and heat transfer in a channel with one wavy wall

Abstract

Large eddy simulation (LES) has been applied to turbulent thermal fields in a channel having one wavy wall for Prandtl number = 0.7. Wall wave amplitude is changed in three steps. Increasing the wall wave amplitude, a flow separation bubble comes to appear and a separated turbulent shear layer develops above the separation bubble. Additionally, in the up-slope region of the bottom wavy wall, near-wall streamwise vortices are generated with larger population. These two turbulence features, i.e., the separated shear layer and the near-wall streamwise vortex, play an important role for the heat and momentum transfer near the wavy wall. So, the characteristics of the separated shear layer and the near-wall streamwise vortices are discussed in relation to the turbulent heat transfer. For this purpose, vortical flow structures aligned toward the streamwise direction and turbulent thermal fields around the vortices were captured and the statistical quantities relating to the turbulent thermal fields were scrutinized. Especially, attention is paid to the effect of the near-wall streamwise vortices on the turbulent heat transfer and the conditionally averaged patterns of turbulent thermal fields around the streamwise vortices were established. The results obtained indicate that the near-wall streamwise vortices produce the strong events of Q T4 and Q T6. Here, Q T4 and Q T6 are cold sweep-like motion and hot ejection-like motion, respectively. Especially, Q T4 event makes the gradient of fluid temperature near the wall steeper in the up-slope region and consequently enhances the heat transfer at the bottom wavy wall. Furthermore, with increasing the wall wave amplitude, the near-wall streamwise vortices were strengthened and as a result the wavy wall heat transfer is more noticeably enhanced. In practical view point, if pumping power is kept the same, better heat transfer performance can be achieved with increasing wall wave amplitude.