AUTHOR=Yu Haidong , Huang Yi , Wang Yiqian , Qian Yuehong , Fu Song 

TITLE=Flow Field Analysis of a Turbulent Channel Controlled by Scalloped Riblets

JOURNAL=Aerospace Research Communications

VOLUME=Volume 1 - 2023

YEAR=2023

URL=https://www.frontierspartnerships.org/journals/aerospace-research-communications/articles/10.3389/arc.2023.12300

DOI=10.3389/arc.2023.12300

ISSN=2813-6209

ABSTRACT=Riblets are small protruding surfaces along the direction of the flow, and have been found to be one of the most known passive turbulent drag reduction methods. We investigate a scalloped riblet whose shape is constructed by smoothly connecting two third-order polynomials, which is not as sharp in the tip and corresponding triangular riblet with same height-width ratio. Numerical simulations are performed for turbulent channel flow with and without riblet control at an estimated optimum width of 𝑊 ! = 20 and a height-width ratio of 0.5. A drag reduction rate 5.77% is obtained, which is generally larger than the reported drag reduction rates of corresponding triangular riblets from the literature. Mean flow fields and second-order statistics of velocity, vorticity and Liutex, a quantity introduced to represent vortices, have been reported. And it is found that streamwise vortices just above the riblet tips, which have a length scale of 200 − 300 in wall units, have important influences towards those statistics and thus the turbulence generation cycle and the drag reduction mechanism. Pre-multiplied energy spectra of streamwise velocity and Liutex component are reported to reveal the length scales in the flow field. Instantaneous vortical flow fields visualized by the Liutex method are provided with emphases on the streamwise vortices just above riblet tips. It should be noted that the class of scalloped riblets could be used to investigate the influences of curvatures at the tip and the valley of the riblet in future.