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首页> 外文期刊>International Journal of Heat and Fluid Flow >Effect of pressure gradients on the different stages of roughness induced boundary layer transition
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Effect of pressure gradients on the different stages of roughness induced boundary layer transition

机译：压力梯度对粗糙度诱导边界层过渡不同阶段的影响

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摘要

The physical mechanisms of roughness-induced transition (RIT) in pressure gradient boundary layers are studied using direct numerical simulations. Recent investigations have examined RIT processes in zero-pressure-gradient boundary layers (Suryanarayanan et al., 2019). The present study uses a vorticity dynamics point of view to examine how these processes are altered by a locally accelerating or decelerating flow that strains the vorticity field and creates a net vorticity flux at the wall. Flow acceleration is imposed on specific streamwise extents of the flow. This provides an understanding about how the fundamental mechanisms in different stages of RIT are affected by pressure gradients. The present results suggest that both lift-up and subsequent amplification of the unsteady perturbations are mitigated by flow acceleration. The effect on lift-up is explained by the compression (i.e. large negative value of the stretching term) of the wall-normal vorticity by negative dv/dy. Consistent with earlier experimental observations on spots and wedges, favorable pressure gradients reduce turbulent wedge spreading and nearly arrest the spreading when sufficiently strong. This result is also explained in terms of vorticity dynamics.
机译：使用直接数值模拟研究了压力梯度边界层中的粗糙感应过渡（RIT）的物理机制。最近的研究已经检查了零压力梯度边界层中的RIT过程（Suryanarayanan等，2019）。本研究使用涡流动力学的观点来检查这些过程的局部加速或减速流程如何改变涡旋场，并在壁上产生净涡流通量。流量加速度施加在流量的特定流动范围内。这提供了关于如何受压梯度的不同阶段的基本机制如何受到压力梯度的影响。本结果表明，通过流量加速来减轻升升和随后的不稳定扰动的扩增。通过阴性DV / Dy的壁正常涡度的压缩（即，拉伸项的大负值）解释对升降的影响。与早期的斑点和楔形的实验观察一致，有利的压力梯度减少湍流楔形蔓延，并且在足够强烈的时差分蔓延。该结果也在涡旋动态方面解释。

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