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首页> 外文期刊>Experiments in Fluids: Experimental Methods and Their Applications to Fluid Flow >Assessment and application of quantitative schlieren methods: Calibrated color schlieren and background oriented schlieren
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Assessment and application of quantitative schlieren methods: Calibrated color schlieren and background oriented schlieren

机译：定量纹影方法的评估和应用：校准的彩色纹影和背景取向的纹影

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Two quantitative schlieren methods are assessed and compared: calibrated color schlieren (CCS) and background oriented schlieren (BOS). Both methods are capable of measuring the light deflection angle in two spatial directions, and hence the projected density gradient vector field. Spatial integration using the conjugate gradient method returns the projected density field. To assess the performance of CCS and BOS, density measurements of a two-dimensional benchmark flow (a Prandtl-Meyer expansion fan) are compared with the theoretical density field and with the density inferred from PIV velocity measurements. The method's performance is also evaluated a priori from an experiment ray-tracing simulation. The density measurements show good agreement with theory. Moreover, CCS and BOS return comparable results with respect to each other and with respect to the PIV measurements. BOS proves to be very sensitive to displacements of the wind tunnel during the experiment and requires a correction for it, making it necessary to apply extra boundary conditions in the integration procedure. Furthermore, spatial resolution can be a limiting factor for accurate measurements using BOS. CCS suffers from relatively high noise in the density gradient measurement due to camera noise and has a smaller dynamic range when compared to BOS. Finally the application of the two schlieren methods to a separated wake flow is demonstrated. Flow features such as shear layers and expansion and recompression waves are measured with both methods. [References: 16]
机译：评估并比较了两种定量的纹影方法：校准的彩色纹影（CCS）和背景取向的纹影（BOS）。两种方法都能够测量两个空间方向上的光偏转角，从而能够测量投影的密度梯度矢量场。使用共轭梯度法进行空间积分将返回投影密度场。为了评估CCS和BOS的性能，将二维基准流（Prandtl-Meyer膨胀风扇）的密度测量值与理论密度场以及从PIV速度测量值推断出的密度进行了比较。还通过实验光线跟踪模拟对方法的性能进行了先验评估。密度测量结果与理论吻合良好。而且，CCS和BOS彼此之间以及相对于PIV测量返回可比较的结果。实践证明，BOS对风洞的位移非常敏感，需要对其进行校正，因此有必要在积分过程中应用额外的边界条件。此外，空间分辨率可能是使用BOS进行精确测量的限制因素。由于摄像机噪声，CCS在密度梯度测量中遭受的噪声相对较高，并且与BOS相比，其动态范围更小。最后，演示了两种schlieren方法在分离的尾流中的应用。两种方法都可以测量流动特征，例如剪切层，膨胀和再压缩波。 [参考：16]

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