标题： 高雷诺数不是湍流边界层中全面对数尺度的必要条件 显示英文标题

标题： Ultra-High Reynolds Number Is Not Necessary for Comprehensive Log Scaling in a Turbulent Boundary Layer

摘要： 在一种被称为汇流的特殊湍流边界层中进行的实验，显示出完美的流向不变性，结果表明流向速度的矩在高达12阶的情况下具有广泛的对数尺度，即使在中等雷诺数下也是如此。 这与典型的恒压湍流边界层形成鲜明对比，后者只有在极高雷诺数下才表现出如此全面的对数尺度。 这表明，全面的对数尺度并不需要极高雷诺数；虽然汇流的具体细节是特殊的，但其对一般湍流边界层的相关性在于，汇流强调了流向不变性条件的重要性，这一条件在一般流动中必须满足才能获得对数尺度。 事实上，一个简单的启发式理论表明，对于惯性子层中的对数尺度，沿平均流线的无量纲平均速度和高阶矩的不变性是一个必要且充分的条件。 极高雷诺数似乎主要使这些对数尺度具有普遍性。 显示英文摘要

摘要： Experiments in an extraordinary turbulent boundary layer called the sink flow, displaying a perfect streamwise invariance, show a wide extent of logarithmic scaling for moments of streamwise velocity up to order 12, even at moderate Reynolds numbers. This is in striking contrast to canonical constant-pressure turbulent boundary layers that show such comprehensive log scaling only at ultra-high Reynolds numbers. This demonstrates that ultra-high Reynolds number is not necessary for comprehensive log scaling to occur; while specific details of the sink flow are special, the relevance to general turbulent boundary layers is that the sink flow underscores the importance of the streamwise invariance condition that needs to be met in a general flow for obtaining log scaling. Indeed, a simple heuristic theory shows that, for log scaling in the inertial sublayer, the invariance of dimensionless mean velocity and higher-order moments along a mean streamline is a necessary and sufficient condition. Ultra-high Reynolds number primarily appears to make these log scalings universal.