Spatial resolution of parallel hot-wire probes for derivative measurements

The spatial resolution of a parallel-wire probe is studied to evaluate the effect of finite wire spacing and wire length on the measurement of turbulence derivative quantities. The study considers the measurement of velocity and temperature derivatives in an isotropoic field. Different spectral models are used for each case to determine if the amount of spatial filtering is sensitive to changes in the shape of the three-dimensional spectrum that is being measured. The data demonstrate that the separation distance is the critical dimension in probe design if the wire length and separation are of comparable magnitude. The amount of spatial filtering predicted is highly sensitive to the spectral model for separation distances greater than 2-3 times the Kolmogorov length scale.