We show that a rather simple, steady modification of the streamwise velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarizes. Two different devices, a stationary obstacle (inset) and a device which injects fluid through an annular gap close to the wall, are used to control the flow. Both devices modify the streamwise velocity profile such that the flow in the center of the pipe is decelerated and the flow in the near wall region is accelerated. We present measurements with stereoscopic particle image velocimetry to investigate and capture the development of the relaminarizing flow downstream these devices and the specific circumstances responsible for relaminarization. We find total relaminarization up to Reynolds numbers of 6000, where the skin friction in the far downstream distance is reduced by a factor of 3.4 due to relaminarization. In a smooth straight pipe the flow remains completely laminar downstream of the control. Furthermore, we show that transient (temporary) relaminarization in a spatially confined region right downstream the devices occurs also at much higher Reynolds numbers, accompanied by a significant local skin friction drag reduction. The underlying physical mechanism of relaminarization is attributed to a weakening of the near-wall turbulence production cycle.

中文翻译：

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通过管道中流向速度剖面的稳定修正进行再分层

我们表明，对管道中的流向速度剖面进行相当简单、稳定的修改会导致湍流完全崩溃并且流动完全重新分层。两种不同的装置，一个固定的障碍物（插图）和一个通过靠近壁的环形间隙注入流体的装置，用于控制流动。这两种装置都修改了流向速度分布，使管道中心的流动减速，而近壁区域的流动加速。我们使用立体粒子图像测速仪进行测量，以调查和捕获这些设备下游的再分层流的发展以及负责再分层的具体情况。我们发现总的再分层高达 6000 的雷诺数，由于再分层，远下游距离的表面摩擦减少了 3.4 倍。在光滑的直管中，流量在控制装置的下游保持完全层流。此外，我们表明，装置下游的空间受限区域中的瞬态（临时）再分层也发生在更高的雷诺数下，伴随着显着的局部皮肤摩擦阻力降低。再分层的潜在物理机制归因于近壁湍流产生周期的减弱。我们表明，在设备下游的空间受限区域中的瞬态（临时）再分层也发生在更高的雷诺数下，伴随着显着的局部皮肤摩擦阻力降低。再分层的潜在物理机制归因于近壁湍流产生周期的减弱。我们表明，在设备下游的空间受限区域中的瞬态（临时）再分层也发生在更高的雷诺数下，伴随着显着的局部皮肤摩擦阻力降低。再分层的潜在物理机制归因于近壁湍流产生周期的减弱。