A study of turbulence under conditions of transient flow in a pipe
A study of turbulence under conditions of transient flow in a pipe
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DOI：
10.1017/s0022112099007016
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发表时间：
2000-04-10
影响因子：
3.7
通讯作者：
Jackson, JD
中科院分区：
文献类型：
--
作者：
He, S;Jackson, JD
以水为工作流体，对管道内完全发育的瞬态流动进行了详细的研究。在稳定的初始值和最终值之间施加线性增加或减少流量的偏移。用三束双分量激光多普勒风速仪同时测量局部速度的轴向和径向分量，或轴向和周向分量。从测量结果中得到了整体平均速度、均方根速度波动和湍流剪应力的值。作为对斜坡型瞬态湍流的第一次真正详细的研究，本研究为湍流动力学的某些基本方面提供了新的信息和有价值的见解。湍流场对施加的流量漂移的响应有一些显著的特征。已经确定了三种不同的延迟：湍流产生响应的延迟；湍流能量在三个分量间再分配的延迟以及与湍流径向传播有关的延迟。在目前的研究条件下，最后一点是最明显的。提出了一个无量纲延迟参数tau(+)[=根2 tau U-tau 0/D]来描述它。发现湍流的第一响应发生在湍流产生峰值的壁面附近区域。湍流的轴向分量比其他两个分量反应更早，积聚得更快。响应通过湍流扩散的作用向管道中心传播，其速度取决于偏移开始时的雷诺数。在核心区，湍流能量的三个分量以相似的方式响应。湍流强度在加速流动时减小，在减速流动时增大。这主要是由于湍流的延迟响应造成的。提出了一个无量纲的斜坡速率参数gamma [= (dU(b)/dt)(1/U-b0)(D/U-tau 0)]，它决定了湍流传播延迟所导致的湍流能量与拟定常流能量的差异程度。
A detailed investigation of fully developed transient flow in a pipe has been undertaken using water as the working fluid. Linearly increasing or decreasing excursions of flow rate were imposed between steady initial and final values. A three-beam, two-component laser Doppler anemometer was used to make simultaneous measurements of either axial and radial, or axial and circumferential, components of local velocity. Values of ensemble-averaged mean velocity, root-mean-square velocity fluctuation and turbulent shear stress were found from the measurements.Being the first really detailed study of ramp-type transient turbulent flow, the present investigation has yielded new information and valuable insight into certain fundamental aspects of turbulence dynamics. Some striking features are evident in the response of the turbulence field to the imposed excursions of flow rate. Three different delays have been identified: a delay in the response of turbulence production; a delay in turbulence energy redistribution among its three components; and a delay associated with the propagation of turbulence radially. The last of these is the most pronounced under the conditions of the present study. A dimensionless delay parameter tau(+)[= root 2 tau U-tau 0/D] is proposed to describe it. The first response of turbulence is found to occur in the region near the wall where turbulence production peaks. The axial component of turbulence responds earlier than the other two components and builds up faster. The response propagates towards the centre of the pipe through the action of turbulent diffusion at a speed which depends on the Reynolds number at the start of the excursion. In the core region, the three components of turbulence energy respond in a similar manner. Turbulence intensity is reduced in the case of accelerating flow and increased in decelerating flow. This is mainly as a result of the delayed response of turbulence. A dimensionless ramp rate parameter gamma [= (dU(b)/dt)(1/U-b0)(D/U-tau 0)] is proposed, which determines the extent to which the turbulence energy differs from that of pseudo-steady flow as a result of the delay in the propagation of turbulence.