Visualization of Instantaneous Density Distribution Based on BOS for Supersonic Flow
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摘要: 瞬态密度场的可视化对于超声速流场复杂流动机理研究有着重要的参考价值.设计了基于脉冲激光照明的瞬态密度场可视化系统，针对非对称尖锥模型在Ф=120 mm激波风洞开展了双方向密度场可视化应用研究，获得了Ma=6条件下激波流场清晰的瞬态和长曝光背景纹影图像.研究表明，瞬态背景纹影图像曝光时间为10 ns，能够有效"冻结"超声速流场；相对于长曝光纹影图像，瞬态图像显示了更小时间尺度的流场密度场，且突起较多，分布不均匀.结果表明，瞬态密度场可视化技术能够揭示瞬态激波流场的密度场细节，为超声速和高超声速流场复杂流动机理的深入理解和研究提供了一种有效方法.Abstract: Visualization of instantaneous density distribution has long been used to contribute to the understanding of complex flows. Using short pulse laser as illumination source, the visualization system of instantaneous density distribution was designed based on background orieted schlieren(BOS) technique. The laser pulse width is 10 ns. Experimental research was carried out with a non-axisymmetrical cone model in the Ф=120 mm shock wind tunnel. The instantaneous and long exposure schlieren images were obtained clearly under the condition of Ma=6. It is shown that the practical integral duration of obtained density distribution of the supersonic flowfield can be very short, as the effective exposure time of capturing instantaneous flow image is 10 ns, which is the pulse width of laser illumination. Compared to the long exposure schlieren images, the instantaneous images display more small time-scale details of supersonic shock flowfield. And it is found that even in a relatively steady shock flowfield during 1 ms, the instantaneous flowfield can be inhomogeneous and distributed with lots of isolated blocks. The experimental results indicate that the visualization system can reveal details of instantaneous shock wave flowfield. It is helpful for deeper study on complex flow mechanism. The visualization system of instantaneous density gradient distribution can be used in various kinds of supersonic or hypersonic flows.
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图 3 测量系统光路图
Figure 3. Schematic diagram of arrangement of optical path in wind tunnel test
图 7 激光脉冲瞬态照明斑点背景
Figure 7. Dot background image captured under instantaneous laser illumination
图 8 1#方向斑点位移量瞬态分布云图(10 ns)
Figure 8. Instantaneous displacement distribution in 1# direction(10 ns)
图 9 2#方向位移量瞬态分布云图(10 ns)
Figure 9. Instantaneous displacement distribution in 2# direction(10 ns)
图 11 1#方向斑点位移量时均分布云图(1 ms)
Figure 11. Long exposure displacement distribution in 1# direction(1 ms)
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