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Large and small scales in a turbulent orifice round jet: Reynolds number effects and departures from isotropy
International Journal of Heat and Fluid Flow ( IF 2.6 ) Pub Date : 2020-06-01 , DOI: 10.1016/j.ijheatfluidflow.2020.108571
G.P. Romano

Abstract An experimental investigation of the near field of a turbulent orifice jet is performed using high resolution Particle Image Velocimetry, aiming to highlight effects on the flow field due to changes in Reynolds number. The attention is focused onto departures from isotropy for large and small scales, by considering statistics of mean square velocity and velocity derivatives and specifically the non-dimensional ratios of such quantities. The results compare well with available literature data and pointed out that the effects of Reynolds number on large scales are usually small and limited to a region ranging less than seven-ten diameters from the jet outlet. For small scales, such Reynolds number dependence is extended up to ten-fifteen diameters. Farther from the jet exit, Reynolds number dependence almost disappears and all data approach similar asymptotic behaviors. On the other hand, velocity and some velocity derivative statistics clearly show that neither large nor small scale statistics strictly follow the isotropy condition; nonetheless, differences from that condition are limited to a factor which is almost constant in the whole measured field. In order to provide a link between such large and small scale departures from isotropy, a relation among mean square velocity ratios and mean square derivative ratios is proposed and proved to be well verified in the measured region and interval of Reynolds numbers. This relation allows deriving small scale derivative ratios, which are difficult to measure experimentally or to obtain numerically, due to high resolution requirements, from large scale velocity ratios, which are achieved much easier.

中文翻译:

湍流孔口圆形射流中的大小尺度:雷诺数效应和各向同性的偏离

摘要 使用高分辨率粒子图像测速仪对湍流孔口射流的近场进行了实验研究,旨在突出雷诺数变化对流场的影响。通过考虑均方速度和速度导数的统计数据,特别是这些量的无量纲比,注意力集中在大尺度和小尺度各向同性的偏离上。结果与可用的文献数据进行了很好的比较,并指出雷诺数在大尺度上的影响通常很小,并且仅限于距离射流出口不到 7-10 直径的区域。对于小尺度,这种雷诺数相关性扩展到十到十五个直径。离喷气式飞机出口更远,雷诺数依赖性几乎消失,所有数据都接近类似的渐近行为。另一方面,速度和一些速度导数统计清楚地表明,无论是大尺度还是小尺度统计都没有严格遵循各向同性条件;尽管如此,与该条件的差异仅限于在整个测量场中几乎恒定的因素。为了提供这种与各向同性的大尺度和小尺度偏离之间的联系,提出了均方速度比和均方导数比之间的关系,并证明在雷诺数的测量区域和区间中得到了很好的验证。这种关系允许从大尺度速度比推导出小尺度导数比,由于高分辨率要求,这些小尺度导数比难以通过实验测量或数值获得,
更新日期:2020-06-01
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