Decomposition of the mean friction drag on an NACA4412 airfoil under uniform blowing/suction
Abstract
The application of dragcontrol strategies on canonical wallbounded turbulence, such as periodic channel and zero or adversepressuregradient boundary layers, raises the question of how to describe control effects consistently for different reference cases. We employ the RD identity (Renard & Deck, J. Fluid Mech., 790, 2016, pp. 339367) to decompose the mean friction drag and investigate the control effects of uniform blowing and suction applied to a NACA4412 airfoil at chord Reynolds numbers Re_c=200,000 and 400,000. The connection of the drag reduction/increase by using blowing/suction with the turbulence statistics (including viscous dissipation, turbulencekineticenergy production, and spatial growth of the flow) across the boundary layer, subjected to adverse or favorable pressure gradients, are examined. We found that the peaks of the statistics associated with the frictiondrag generation exhibit good scaling in either inner or outer units throughout the boundary layer. They are also independent of the Reynolds number, control scheme, and intensity of the blowing/suction. The small and largescale structures are separated with an adaptive scaledecomposition method, i.e. empirical mode decomposition (EMD), aiming to analyze the scalespecific contribution of turbulent motions to frictiondrag generation. Results unveil that blowing on the suction side of the airfoil is able to enhance the contribution of largescale motions and to suppress that of smallscales; on the other hand, suction behaves contrarily. The contributions related to crossscale interactions remain almost unchanged with different control strategies.
 Publication:

Journal of Fluid Mechanics
 Pub Date:
 February 2022
 DOI:
 10.1017/jfm.2021.1015
 arXiv:
 arXiv:2106.03547
 Bibcode:
 2022JFM...932A..31F
 Keywords:

 Physics  Fluid Dynamics
 EPrint:
 doi:10.1017/jfm.2021.1015