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首页> 外文期刊>Experiments in Fluids: Experimental Methods and Their Applications to Fluid Flow >Effects of imaging system blur on measurements of flow scalars and scalar gradients
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Effects of imaging system blur on measurements of flow scalars and scalar gradients

机译：成像系统模糊对流量标量和标量梯度测量的影响

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Planar imaging of flow scalars is widely used in fluid mechanics, but the effects of imaging system blur on the measured scalar and its gradients are often inadequately quantified. Here, we present a 1-D analytical study that uses simplified models of the scalar profiles and imaging system blur to estimate the measurement errors caused by finite resolution. One objective of this paper is to give the experimentalist a methodology for quantitatively assessing the impact of imaging system blur on the accuracy of scalar measurements. The scalar profiles are modeled as either error or Gaussian functions, and the imaging system resolution is cast in terms of the line-spread function (LSF), which is modeled as Gaussian. The analysis gives the errors induced in the scalar structure thickness, gradient, and dissipation, for varying degrees of blur, the latter of which is quantified by sigma, the standard deviation of the Gaussian LSF. The results show that, to keep errors in the peak scalar gradients and dissipation to less than 10%, the 20%-width of the scalar structures should be at least 7.5sigma. Typical flow imaging experiments require fast (i.e., low f/#) optics that may suffer from significant blur and, therefore, this requirement may be difficult to meet in many applications. It is also shown that the resolution requirements for measuring the dissipation are more restrictive than for structure thicknesses. Further simulations were made to assess the effects of having clustered, or closely spaced, dissipation structures. Compared to the single structure results, there is a less severe resolution requirement to obtain scalar structure length scales, but a more severe requirement on the scalar gradient and dissipation.
机译：流标量的平面成像在流体力学中得到了广泛的应用，但是成像系统模糊对所测量的标量的影响及其梯度通常无法充分量化。在这里，我们提出了一维分析研究，该研究使用标量轮廓和成像系统模糊的简化模型来估算由有限分辨率引起的测量误差。本文的目的是为实验人员提供一种定量评估成像系统模糊对标量测量精度影响的方法。标量轮廓被建模为误差函数或高斯函数，并且成像系统分辨率根据被建模为高斯的线扩展函数（LSF）进行转换。分析给出了在标量结构厚度，梯度和耗散中由于不同程度的模糊而引起的误差，其中模糊程度由sigma（高斯LSF的标准偏差）量化。结果表明，为使​​峰值标量梯度和耗散误差保持在10％以下，标量结构的20％宽度应至少为7.5sigma。典型的流量成像实验需要快速（即低f /＃）光学器件，这些光学器件可能会遭受明显的模糊，因此，在许多应用中可能很难满足这一要求。还表明，测量耗散的分辨率要求比结构厚度的要求更高。进行了进一步的仿真，以评估具有聚集的或紧密间隔的耗散结构的影响。与单一结构的结果相比，获得标量结构长度标尺的分辨率要求不那么严格，但对标量梯度和耗散的要求更严格。

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