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Calibration of an X-wire with Assessment of a Moderately High Reynolds Number Flow

Abstract

A new, wider angle calibration of the X-wire utilizing a polynomial surface fit is introduced and its abillity to accurately measure a self-preserving, homogenous, active grid generated turbulent flow is examined. In this assessement, the longitudinal statistical and spectral data obtained by an X-wire are compared with corresponding values obtained by a single hot-wire. Specifically, the normalized velocity variance and dissipation obtained through the velocity derivative show a maximum difference of 5% and 4%, respectively between the two sensors. Spectral comparisons also show an oscillating ratio around 1 for the X-wire spectral values over the single hot wire spectral values and indicate good agreement over a wide range of wavenumbers. In evaluating the moderately high turbulence intensity flow, X-wire measurements show that the flow is sufficiently locally isotropic using the comparison of the longitudinal and transverse velocity derivative variance as well as using the comparison of the longitudinal and transverse spectra. In addition〖,ϵ〗^*, the dissipation obtained from the power decay law of turbulent kinetic energy, shows a 25% overestimation when the turbulent kinetic energy, q, is taken as 3/2 (u^2 ) ̅ as opposed to 1/2((u^2 ) ̅+(v^2 ) ̅+(w^2 ) ̅) at 12 ms-1. At the same mean velocity, the dissipative ratio, ϵ/ϵ^* , where ϵ is the dissipation obtained from the velocity derivative, is underestimated by 18%.

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