STUDYING THE UNSTEADY, THREE-DIMENSIONAL CHARACTERISTICS OF FLOW REATTACHMENT(Separation and Reattachment)

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This paper reports on the results of using thermal-sensitive liquid crystal to study the unsteady, three-dimensional characteristics of flow reattachment on a rectangular block. The aspect ratio of the block, i. e., streamwise length versus height, was 2. A liquid crystal film sensitive to a temperature range of 40℃-50℃ was applied on the top surface of the block. The experiment was made with the block heated to 49.5℃, subjected to a uniform flow at room temperature in a low-speed wind tunnel. The liquid crystal images obtained by a CCD camera were expressed in terms of the hue level distributions for quantitative analysis. At Re=5.37×10^4, the video images show that the reattachment length x_R was varying between 1 to 1.5h, where h denotes the height of the block. Comparing the video images obtained at every 1/15 seconds, roughly 20 x_R/U_0, revealed the low-frequency unsteadiness of flow reattachment. Moreover, the finger-type image patterns noted immediately downstream of flow reattachment appeared unsteady in time and random in space. The spanwise extents of these structures were estimated to be 0.5-0.8h or 0.3-0.5x_R, which were suspected to be associated with the vortical structures developed in the separated shear layer.
一般社団法人日本機械学会の論文
2005-10-05