压缩-膨胀湍流边界层平均摩阻分解

Decomposition of mean friction drag in compression-expansion turbulent boundary layer

采用直接数值模拟对来流马赫数2.9、24°压缩-膨胀折角构型中激波与湍流边界层干扰问题进行了研究。重点关注膨胀折角法向高度对激波干扰区以及下游平板边界层流动的影响。研究发现,当高度足够大时,激波干扰区内未受下游膨胀波的影响,此时的流动特征与传统的压缩折角干扰构型一致。高度较小时,脱体剪切层的再附过程受到下游膨胀波的加速影响,导致再附点向上游移动,分离泡发生剧烈收缩。对上、下游平板湍流边界层应用了平均摩阻分解技术,比较了湍流边界层在平衡和非平衡状态下的差异。分析发现,膨胀折角区域的高摩阻现象主要与摩阻分解后的C_(f1)项与C_(f3)项相关。高度变化对C_(f1)项影响较小,而对C_(f2)项影响显著。高度变化体现在:下游平板上Görtler涡结构强度以及层流化现象对C_(f2)项贡献的差异。

The interaction between the shock wave with Mach number 2.9 and the turbulent boundary layer in the configuration of 24°compression-expansion corners is investigated by using direct numerical simulation.The influence of normal height of the expansion corner on the shock wave interaction region and downstream boundary layer is analyzed.It is found that when the height is large enough,the shock wave interaction region is not affected by the downstream expansion wave,and the characteristics are consistent with those of the traditional compression corner configuration.While the height is small,the reattachment process of the detached shear layer is accelerated by the downstream expansion wave,which causes the reattachment point to move upstream and the separation bubble to shrink dramatically.The decomposition of mean friction drag is applied to the turbulent boundary layer of the upstream and downstream plates,and the difference between the turbulent boundary layer in equilibrium and nonequilibrium state is explored.It is found that the high friction in the expansion corner is mainly related to the C_(f1) term and C_(f3) term in the decomposition of mean friction drag.The height has little effect on the C_(f1) term,while significant effect on the C_(f2) term.Height variation is reflected in the contribution of the Görtler vortex and re-laminar phenomenon on the downstream plate to the C_(f2) term.