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13th Spring School on Transition and Turbulence
Random errors in hot-wire anemometry using synthetic data
Livia S. Freire , SP
Co-Authors: Livia S. Freire
Presenter: Livia S. Freire
Hot-wire anemometers are one of the main tools used in the measurement of rapid velocity fluctuations in laboratory and natural flows. Their measurement frequency, which can reach the order of kilohertz, allows the investigation of turbulence fluctuations down to the smallest (dissipative) scales, providing a comprehensive description of turbulent flows. In this study, synthetic data that mimic hot-wire time-series velocity measurements are used to investigate random errors and their impact on turbulence statistics. The synthetic data are obtained from a prescribed three-dimensional energy spectrum, which includes the production, inertial and dissipation ranges in addition to the bottleneck and intermittency effects (Meyers & Meneveau, 2008), superposed by random errors following a chi-square distribution. The theoretical spectrum has a predefined Reynolds number, dissipation rate and mean streamwise velocity (used in the Taylor’s frozen turbulence hypothesis). From this spectrum, single-point time-series of the three velocity components are obtained from a simple method based on the inverse Fourier transform and the Monte Carlo approach, assuming a homogeneous, isotropic and stationary flow. The probability distribution of turbulence statistics impacted by the random errors can be readily calculated from the synthetic time-series. Examples of statistics include the dissipation rate and isotropic ratios estimated from one-dimensional energy spectra or second-order structure functions, for example, providing reliable information on error and bias. Finally, the method can also serve other purposes, including educational training, code verification and validation, experiment planning, and testing and visualization of other types of measurement errors. Reference Meyers, J. & Meneveau, C. (2008). A functional form for the energy spectrum parametrizing bottleneck and intermittency effects. Physics of Fluids, 20(6), 065109.
Random erros, synthetic data, velocity time-series, Turbulence