An examination of hot-wire length corrections

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Abstract
A comprehensive experimental examination is presented of the effect of hot‐wire length for a single‐wire probe. Specially constructed hot wires, with 2.5 μm and 5.0 μm nominal diameters and lengths from 0.3 mm to 2.8 mm, were used to measure the one‐dimensional spectrum of the streamwise fluctuating velocity component u as well as the skewness and flatness of both u and du/dt. All measurements were made in air at Y+=150 (corresponding to Y/δ=0.1) in a boundary layer growing inside a pipe. The Reynolds number was 37 000 based on the velocity at the centerline and on the boundary‐layer thickness. The longest wires exhibited some attenuation at the highest wavenumbers. This attenuation was found to roughly confirm the correction to the spectrum due to Wyngaard. A correction for the microscale λ, and thus dissipation, was examined and found to be correct to a fair degree (within 8%). This correction is based on the early work of Skramstad and of Frankiel, but with the integral scale of R11 (0, 0, r) assumed to equal the λ scale. The measurements of skewness and flatness did not indicate an experimentally discernible effect of the length of the hot wire.

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