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外加非对称扰动对园管内湍流壁面剪切应力的影响
周达文
Subtype硕士
Thesis Advisor陈家镛
1988-06-30
Degree Grantor中国科学院研究生院
Abstract为进一步考察外加扰动对湍流壁面附近的流动特性的影响,本研究采用了一种与众不同的扰动方式-外加非对称锯齿速度波形扰动,利用电化学实验技术测量了壁面速度梯度(或剪切应力)及湍流强度等对外加扰动的响应;并应用带有压力梯度松驰的涡团粘性模型进行了模拟。在相对振幅0.05-0.15、无因次振荡频率从0.0043到0.0647的范围内进行实验的结果表明:外加非对称锯齿波形扰动对湍流流动的时均性质影响不明显。相均壁面速度梯度和湍流强度响应波形与外加的非对称锯齿扰动波形相同;相均壁面速度梯度响应的非对称波形与相均湍流强度的波形变化趋势几乎正好相反,即相均速度梯度增大时,湍流强度减弱,而当相均壁面速度梯度减少时,湍流强度增大。本研究第一次通过外加扰动实验非常直观地证实了:正向压力梯度(dP/dX < 0)(即在流动的加速相)对湍流有抑制作用,而反向压力梯度(dP/dX > 0)(即在流动的减速相)对湍流有增强效应。另外相均壁面速度梯度的峰值特性和相移变化与对称扰动时的幅值特性和相位滞后的变化趋势类似,但值的大小相差较大。模型的数值计算结果表明:能较好地模拟对称扰动(特别是正弦扰动)时湍流流动的带有压力梯度松弛的粘性涡团模型,不能模拟本研究采用的非对称扰动时的管内湍流流动。要想更为有效地研究这种新的扰动方式(非对称扰动)下的湍流流动特性,需要探寻一种新的模拟方法。
Other AbstractThis study investigated the influences of a non-sinusoidal flow oscillation on the characteristics of turbulent pipe flow with a distinctive wave pattern of flow oscillation, i.e., an asymmetrical sawtooth wave, superimposed on the mean flow. The responses of the turbulent intensity of velocity gradient at the wall to the imposed flow oscillation were measured with electrochemical technique. A turbulent eddy viscosity model was used to simulate the unsteady turbulent pipe flow. From the experimental results, no significant influences of the imposed asymmetrical flow oscillation on the time averaged turbulent flow were observed at the amplitude between 0.05 and 0.15 and dimensionless oscillating freqency from 0.0043 to 0.0647. The responsed wave shape of the phase averaged wall velocity gradient and the phase averaged turbulent intensity of velocity gradient are similar to that of the imposed flow oscillation. However, the variation of the velocity gradient at the wall was nearly adverse to that of the phase averaged turbulent intensity of velocity gradient. That means the phase averaged turbulent intensity decreases with the increase of the phase averaged velocity gradient at the wall, and vice versa. This is the first time in the unsteady flow to confirm that imposing a favorable pressure gradient (dP/dX < 0, in the accelerated flows) constricts turbulence in the viscous wall region and an unfavorable pressure gradient (dP/dX > 0, in the decelerated flows) enlarges the turbulence. Both the amplitude and the phase of the phase averaged velocity gradient at the wall are related to dimensionless frequency of the flow ocillation, ω~+, in the similar way to that in the sinusoidal flow oscillation, but are in different values. The numerical results show that the relaxion model of turbulent eddy viscosity, which can adequately simulate the turbulent pulsating pipe flow with symmetrically sinusoidal oscillation, fails to simulate the asymmetrical pulsating flow. It is necessary to develop a new model to simulate the asymmetrical pulsating flow.
Pages75
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/8432
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
周达文. 外加非对称扰动对园管内湍流壁面剪切应力的影响[D]. 中国科学院研究生院,1988.
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