Effects of imperfect spatial resolution on turbulence measurements in the very near-wall viscous sublayer region

Abstract

 Experiments were carried out to study the effects of imperfect spatial resolution on turbulence measurements in the very near-wall region using hot wires of different lengths, l ⁺ (in wall units). Previous works have indicated that the distributions of the longitudinal velocity rms value, skewness and flatness factors are independent of l ⁺ in the buffer region and beyond provided l ⁺<20–25. Our results obtained using l ⁺=3, 6, and 22 in the viscous sublayer region show that generally the said distributions are dependent on l ⁺ and attentuate in magnitude with increasing l ⁺. Further experiments were also carried out at different Reynolds numbers (Re _c , based on centerline velocity and channel’s height) but with measurements made using hot wire of the same l ⁺. The latter shows that the rms value and other higher order moments of longitudinal velocity fluctuations are independent of Re _c , thereby extending similar findings by Johansson and Alfredsson (1983), valid in the buffer region into the viscous sublayer region.