后向台阶绕流低频脉动特性的强化传热研究

Effect of Low Frequency Fluctuation on Heat Transfer Enhancement in Backward-Facing Step Flow

后向台阶绕流是包含丰富流动现象的典型分离再附流动,在工程中应用广泛。这里针对过渡流下后向台阶绕流低频脉动特性对传热的影响展开研究,重点分析了主回流区再附着点下游传热得到强化的原因。结果表明:过渡流下的低频脉动特性诱导流动在壁面附近形成旋涡,这些旋涡的运动破坏了速度边界层的均匀发展,同时加强了冷热流体的混合,从而强化了底面传热,再附着点下游局部区域的传热比层流时提升了3倍以上。随着雷诺数的继续增大,近壁旋涡的形态发生变化,促使流体冲击壁面的角度增大,低速回流范围减小,从而进一步强化了底面传热。

The backward-facing step flow is a typical separation and reattachment flow with various flow phenomena.It is widely involved in industry.The effects of low frequency fluctuation on heat transfer in the transitional flow over a backward-facing step are studied.The reason for heat transfer enhancement downstream of the reattachment is analyzed.The results show that the vortices in the vicinity of channel wall are induced by the low frequency fluctuation in the transitional flow.The velocity boundary layer is destroyed and the mix of cold fluid and hot fluid is enhanced by these vortices.Thus,the heat transfer of bottom wall is enhanced more than 3 times in the local area downstream of the reattachment.The vortex shape changes with the increase of Reynolds number,which leads to the increase of attack angle and the decrease of backflow region.Thus,the heat transfer of bottom wall is further enhanced.