Shear stress fluctuation measurements using an electrochemical method in pipe flow

Abstract

Wall shear stress fluctuations are measured using an electrochemical method in pipe flow. The relationship between the mass transfer and the momentum transfer, studied by Hanratty and Campbell (1983) and the Chilton–Colburn analogy (Chilton and Colburn, 1934), are compared to each other with respect to the mean wall shear stress and the wall shear stress fluctuation. Chilton–Colburn analogy has been applied to measure the mean wall shear stress in the fully developed concentration boundary layer. There are few studies concerning the feasibility of the Chilton–Colburn analogy for instantaneous wall shear stress measurements. In the present study, with the new designed overall electrode, the feasibility of Chilton–Colburn analogy for predicting the wall shear stress fluctuations is studied for the first time. The friction factor is used to compare the mean wall shear stresses. It is found that both methods can accurately predict the mean wall shear stress. The wall shear stress fluctuations are compared via the probability density function and frequency spectrum. When the probability density fluctuation is normalized by the standard deviation and the spectrum is normalized by the typical time scale, these two methods show the similar statistical properties. It is confirmed that with the new designed overall electrode, Chilton–Colburn analogy is available for predicting the wall shear stress fluctuations.

Keywords

• wall shear stress fluctuation
• chilton–colburn analogy
• electrochemical method
• pipe flow
• simultaneous measurement