圆湍射流控制的实验研究

Experimental Study on the Control of a Round Turbulent Jet

本文以圆湍射流为对象，研究了初始扰动参数的改变对湍流拟序结构发展的影响。当雷诺数Ｒｅ＝２９３８，５６４０，１１７５０，以及扰动Ｓｔｒｏｕｈａｌ（Ｓｒ）数在０～０．９范围变化时，通过流场显示，对射流喷口附近过渡区的拟序结构演变过程进行了观测。实验发现，在Ｓｔｒｏｕｈａｌ数为０．５左右时，射流核心区长度最短，拟序结构的发展最显著，且对Ｒｅ数不敏感；拟序结构随初始扰动振幅的增大而增长，但扰动幅值增大到一定程度后，涡的增长趋于不明显。本研究为通过控制湍流拟序结构进而控制湍流提供了初步依据。

The role of initial disturbance parameters (the frequency and amplitude of a sine vibration) on the evolution of coherent structures of a round turbulent jet is examined experimentally.The jet flow Reynolds numbers,which is determined by the mean jet exit velocity and the nozzle diameter,are 2 938,5 640,11 750 respectively.The disturbance frequency is governed by the dimensionless Strouhal number,which falls into the range of 0～0.9 in present research.Detailed instantaneous images of the coherent structures in the proximal region ( x/D <10) of the round jet have been obtained.It is shown that a minimum length of the potential core regime and the full extents of the jet coherent structures emerge in the neighborhood of 0.5 of the Strouhal number.The influence of Reynolds numbers on the coherent structures becomes insensitive at these Strouhal numbers.The effect of the disturbance amplitudes on the development of the large scale structures is also studied.The variance of the structures induced by the disturbance is no longer detective when the disturbance amplitude excesses a certain value.The current research provides the basis of investigating the control of turbulent shear flows through coherent structures.