Author(s): Ming Jin

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Abstract: A two-tube method is proposed to extend the Preston tube technique for determining the local shear stress in both rough and smooth surfaces. The analytical calibration functions of the Preston tube are derived based on the Rotta's model for the velocity profile on smooth and rough surfaces and a formula for the displacement factor of the Preston tube. The new method, unlike the conventional Preston tube method, is a combination of the measurement by two tubes of different diameters and iterative computation by the analytical calibration functions to determine the roughness parameter and local shear stress. The analytical calibration curves are compared with experimental data. The use of the two-tube method on the smooth surface is verified by experiment.

DOI: https://doi.org/10.1080/00221689509498579

Year: 1995