Skin friction measurements using oil film interferometry and Preston tube at subsonic/transonic regime
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摘要: 在0.6m×0.6m亚跨超声速风洞中,采用油膜干涉测量技术(OFI)和Preston管方法开展了马赫数0.4~0.8下的平板模型表面摩擦应力测量实验研究。模型头部经过椭圆化处理,避免出现流动分离。实验发现:在亚跨声速条件下,两种方法的测量结果具有很好的一致性;油膜粘性对摩擦应力测量结果影响很小;当来流马赫数或总压发生变化时,摩擦应力系数随来流动压或马赫数与雷诺数的乘积(Ma·Re)的增大而减小。在Ma=0.4和0.6时,观测到一种类似斑纹的干涉图像,基于其特性分析,提出以此作为一种转捩判据的设想;在Ma=0.8时,未观察到类似斑纹,根据油膜图像和数值模拟结果判断,模型头部出现了分离泡,边界层由分离诱导转捩。Abstract: Measurements of skin friction on a flat plate model were conducted in the 0.6m×0.6m subsonic/transonic/supersonic wind tunnel. Oil film interferometry (OFI) and Preston tube technique were applied to obtain the skin friction data at Ma=0.4~0.8. In order to avoid flow separation, an elliptical leading edge was employed. Results indicate that the agreement between OFI and Preston tube is very well. Viscosity of oil film has little influence on the skin friction measurement. When the stream's Mach number or the total pressure changes, the skin friction coefficient decreases along with the increase of the dynamic pressure or the product of Mach number and Reynolds number (Ma·Re). A freckle-like interference pattern was observed at Ma=0.4 and 0.6, and an assumption based on the new pattern was proposed to determine the transition location. According to the oil motion and CFD results, a separation bubble rather than the new pattern appears at Ma=0.8, and it is responsible for the transition of boundary layer.
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Key words:
- OFI /
- Preston tube /
- skin friction /
- transition /
- separation
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表 1 实验状态参数
Table 1. Parameters of test conditions
Ma Cf(x=55mm) q/Pa Re(L=0.6m) Ma·Re 0.400 (Conventional) 0.0052 9 740 4.95×106 1.98×106 0.577 (Pressured) 0.0040 26 970 9.90×106 5.71×106 0.600 (Conventional) 0.0045 20 350 7.20×106 4.32×106 0.800 (Conventional) 0.0037 32 830 9.40×106 7.52×106 表 2 斑纹图像位置(斑纹中心)
Table 2. Positions of freckle-like interference pattern
Ma Re(L=0.6m) x/mm 0.4 4.95×106 32~33 0.6 9.90×106 27~28 -
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