Abstract
We present experimental Lagrangian measurements of tracer particle acceleration autocorrelation functions in an anisotropic and inhomogeneous flow spanning the typical range of experimentally accessible Reynolds numbers. The large-scale forcing of the flow creates a stagnation point topology where straining motion governs the anisotropic velocity and acceleration fluctuations. We show that the timescales of the acceleration components remain anisotropic at high Reynolds numbers and that they are related to the dissipative timescale by the Lagrangian structure function scaling constants and , as well as , which is shown to be kinematically related to the velocity increments. The proposed scaling relation is supported by observations using experimental Lagrangian trajectory data sets and analytical calculations using a jointly Gaussian two-time stochastic model. Examination of acceleration power spectra show that acceleration fluctuations become isotropic in the dissipative range, which suggests that the acceleration timescale is determined not only by small scales, but also by large and anisotropic scales whose contributions are substantial, even in the high Reynolds number limit.
- Received 8 December 2018
DOI:https://doi.org/10.1103/PhysRevFluids.4.064606
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