Volume 38, Number 2, April 2020
|Page(s)||253 - 260|
|Published online||17 July 2020|
Determination of Wall Friction Velocity of the Turbulent Boundary Layer by Two-Parameter Nonlinear Curve Fitting
School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China
Hot-wire anemometer is a fundamental tool for flow field measurement, and has been widely adopted in research of turbulent flow. A turbulent boundary layer was generated by a trip wire and a piece of sandpaper in the low-speed wind tunnel, and the time-averaged velocity profiles at three different streamwise stations in the boundary layer were measured with IFA-300 constant temperature anemometer. Targeting the dimensionless velocity profile model White Law of the turbulent boundary layer, a nonlinear curve fitting MATLAB program for two parameters, which were theoretical original point of wall coordinate y0 and wall friction velocity uτ, was developed. Based on the measured time-averaged velocity profiles, the program was adopted to determine y0 and uτ of the three streamwise stations. It is found that the initial search domain and search step size of y0 and uτ have no effect on the fitting results if the physical solutions are included in the domain. It is also found that the selected fitting velocities data are closely related to the results. The value of the friction velocity with high precision will be obtained by this nonlinear curve fitting method if the highest fitting velocity data point dose not fall into the wake region. The method given in this paper is simple in programming and reliable in fitting results, and it is of practical to obtain the wall friction velocity of the turbulent boundary layer.
Key words: turbulent boundary layer / White Law / dimensionless velocity profile / wall friction velocity / nonlinear curve fitting / hot-wire anemometer / MATLAB program
关键字 : 湍流边界层 / White Law / 无量纲速度型 / 壁面摩擦速度 / 非线性拟合 / 热线风速仪 / MATLAB程序
© 2019 Journal of Northwestern Polytechnical University. All rights reserved.
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