On the accuracy of measurement of turbulent velocity gradient statistics with hot-wire probes
2017
A very high resolution minimal channel flow DNS was used to examine,
virtually, the ability of various multi-sensor hot-wire probe configurations
to measure the statistics of velocity gradient components. Various array and
sensor configurations and the spatial resolution of probes with these
configurations were studied, building on designs and investigations of
various authors. In contrast to our previous studies, which focused on
turbulent vorticity, vorticity-velocity correlations, dissipation and
production rate, here the measurement accuracy of each component of the
velocity vector gradient tensor is analyzed separately. The results of the
study show that the virtual experiments compare well with a physical
experiment, and that such virtual experiments are a powerful tool to examine
the accuracy of velocity gradient measurements. The cross-stream gradients
needed to determine the vorticity components can be measured with sufficient
accuracy with most of the array and sensor configurations of vorticity probes
used so far. A systematic error of some of the gradient measurements can
appear due to the array or sensor configurations. None of the examined probe
designs can measure, with sufficient accuracy, the stream-wise velocity
gradients, directly or indirectly, using the continuity equation.
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