Nihon Kikai Gakkai ronbunshu (May 2014)
A study on effects of temporally varying/ fluctuating noises on statistical profiles measured by means of PLIF method (Development of prediction formulas of the effects, and validation by high-Sc-number scalar mixing layer in grid turbulence)
Abstract
In planar laser induced fluorescence (PLIF) measurement, temporally varying and fluctuating noises affect measured statistical profiles, significantly. In this study, the former φ is caused by a ratio of temporally varying quantum yield φ between measurement and reference images, and the latter sβI is mainly due to temporal fluctuations of a ratio of camera sensitively β and a ratio of incident laser I to excite a fluorescent dye, where sβI ≡ βI - 1. These noises can significantly affect statistical profiles of fluctuating concentration field. The aim of this study is to develop predictive formulas for the effects on fundamental statistical profiles. The effects of φ and sβI are reconstructed to mean of φ, αT/2, mean of sβI, SβI and intensity of fluctuation of sβI, <e2>, where α is rate of temporal change of φ, T is required time of the experiment, SβI = <sβI>, e = sβI, sβI = SβI + sβI and <> denotes ensemble average. Then, we show a series of the formulas to predict the effects on mean scalar, intensity of scalar fluctuation, 3rd-order statistics and 4th-order statistics of scalar fluctuation. The predictive formulas are validated by using experimental results of high-Sc-number scalar mixing layer in grid-generated turbulence measured by PLIF method, where the mesh Reynolds number was 2,500 and the Schmidt number was about 2,100, respectively. The effects of <e2> is analytically found to be the most significant among αT, SβI and <e2> by expanding the predictive formulas. In fact, the profile of <c2> is significantly affected by variation of <e2>. The predictive formulas can be used as formulas to correct the profiles when given values of the three parameter are appropriate.
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