Improved space-time correlation estimates from single-point velocity measurements
Tropea, C.; Nobach, H.
Division of Fluid Dynamics 56th Annual Meeting, November 23-25, 2003, East Rutherford, New Jersey, USA
An integral time-to-length transform is introduced to account for temporal velocity fluctuations not foreseen in a simple application of Taylor's hypothesis. This allows an improved estimate of the space-time correlation function of velocity, using as a base estimate the single-point spatial correlation. However also the estimate of this spatial correlation can be greatly improved using the measured, single-point temporal correlation function. Essentially, a better estimate of the length of a stream filament passing through the measurement point in a given time has been achieved, knowing the temporal correlation function. The improvement is particularly significant for larger time lags. All estimates benefit from a model-based noise removal, applied at the structure function level. Finally, some remarks are directed towards implementation of the technique to irregularly sampled laser Doppler data, although the technique can be used with any single-point velocity measurement technique, e.g. hot-wires. The performance of the new estimator is evaluated by comparing single-point and two-point laser Doppler measurements in a turbulent free jet.
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