Dynamic wall-shear stress measurements in turbulent pipe flow using the micro-pillar sensor MpS3

The micro-pillar wall-shear stress sensor MpS(3) has been used to measure the dynamic wall-shear stress in turbulent pipe flow. The sensor device consists of a flexible micro-pillar which extends from the wall into the viscous sublayer. The pillar-tip deflection caused by the exerting fluid forces serves as a measure for the local wall-shear stress. The pillar is statically calibrated in linear shear flow. A second-order estimate of the pillar dynamic response based on experimentally deter-mined sensor characteristics shows the potential of the present sensor configuration to also measure the dynamic wall-shear stress. The quality of the micro-pillar shear stress sensor MpS(3) to correctly determine the skin friction will be shown by measuring the wall friction in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re-b based on the bulk velocity U-b and the pipe diameter D in the range of Re-b = 10, 000-20, 000. The results demonstrate a convincing agreement of the mean and dynamic wall-shear stress obtained with the MpS3 sensor technique with analytical, experimental, and numerical results from the literature. (C) 2008 Elsevier Inc. All rights reserved.