Resolvent Analysis of Turbulent Friction Drag Reduction by Manipulation of Mean Velocity Profile

2019 ◽  
Author(s):  
Riko Uekusa ◽  
Aika Kawagoe ◽  
Yusuke Nabae ◽  
Koji Fukagata
Keyword(s):  
Velocity Profile ◽  
Drag Reduction ◽  
Turbulent Viscosity ◽  
Turbulent Channel Flow ◽  
The Other ◽  
Friction Drag ◽  
Mean Velocity ◽  
Turbulent Friction ◽  
The Mean ◽  
Friction Drag Reduction

Abstract In the present study, we numerically manipulate the mean velocity profile of a turbulent channel flow and assess the friction drag reduction performance by using resolvent analysis. Building on the implication obtained from Kühnen et al. (Nat. Phys., Vol. 14, 2017, pp. 386–390) that modifying mean velocity profile flat leads to significant drag reduction, we first introduce two functions for turbulent mean velocity, which can express ‘flattened’ profiles: one is derived based on the turbulent viscosity model proposed by Reynolds & Tiederman (J. Fluid Mech., Vol. 658, 2010, pp. 336–382), and the other is based on the mean velocity profile of laminar flow. These functions are used as the mean velocity profile for the resolvent analysis, and the flatness of the resulting profiles is characterized by two different measures. As a result, we confirm that, friction drag reduction is achieved if the turbulent mean velocity profile is ‘flattened’. However, we also find that the flatness of the mean velocity profile in the center of the channel alone is not enough to evaluate the drag reduction performance.

Turbulent Friction Drag Reduction on Clark-Y Airfoil by Passive Uniform Blowing

AIAA Journal ◽  
2020 ◽  
Vol 58 (9) ◽  
pp. 4178-4180
Author(s):  
Shiho Hirokawa ◽  
Masahiro Ohashi ◽  
Kaoruko Eto ◽  
Koji Fukagata ◽  
Naoko Tokugawa
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Turbulent Friction ◽  
Friction Drag Reduction

115 Optimization of an anisotropic compliant surface for turbulent friction drag reduction(1)

2007 ◽  
Vol 2007 (0) ◽  
pp. _115-a_
Author(s):  
Koji FUKAGATA ◽  
Stefan KERN ◽  
Philippe Chatelain ◽  
Petros KOUMOUTSAKOS ◽  
Nobuhide KASAGI
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Turbulent Friction ◽  
Compliant Surface ◽  
Friction Drag Reduction

115 Optimization of an anisotropic compliant surface for turbulent friction drag reduction(2)

2007 ◽  
Vol 2007 (0) ◽  
pp. _115-1_-_115-4_
Author(s):  
Koji FUKAGATA ◽  
Stefan KERN ◽  
Philippe Chatelain ◽  
Petros KOUMOUTSAKOS ◽  
Nobuhide KASAGI
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Turbulent Friction ◽  
Compliant Surface ◽  
Friction Drag Reduction

Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids

1982 ◽  
Vol 119 ◽  
pp. 423-441 ◽  
Author(s):  
M. A. Goldshtik ◽  
V. V. Zametalin ◽  
V. N. Shtern
Keyword(s):  
Velocity Profile ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Outer Boundary ◽  
Viscous Sublayer ◽  
Viscous Layer ◽  
Mean Velocity ◽  
Turbulent Layer ◽  
The Mean ◽  
Near Wall

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.

scholarly journals High-resolution velocity measurement in the inner part of turbulent boundary layers over super-hydrophobic surfaces

2016 ◽  
Vol 801 ◽  
pp. 670-703 ◽  
Author(s):  
Hangjian Ling ◽  
Siddarth Srinivasan ◽  
Kevin Golovin ◽  
Gareth H. McKinley ◽  
Anish Tuteja ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Velocity Profile ◽  
Drag Reduction ◽  
Slip Velocity ◽  
Reynolds Shear Stress ◽  
Turbulent Boundary Layers ◽  
Mean Velocity ◽  
Roughness Elements ◽  
The Mean

Digital holographic microscopy is used for characterizing the profiles of mean velocity, viscous and Reynolds shear stresses, as well as turbulence level in the inner part of turbulent boundary layers over several super-hydrophobic surfaces (SHSs) with varying roughness/texture characteristics. The friction Reynolds numbers vary from 693 to 4496, and the normalized root mean square values of roughness $(k_{rms}^{+})$ vary from 0.43 to 3.28. The wall shear stress is estimated from the sum of the viscous and Reynolds shear stress at the top of roughness elements and the slip velocity is obtained from the mean profile at the same elevation. For flow over SHSs with $k_{rms}^{+}<1$, drag reduction and an upward shift of the mean velocity profile occur, along with a mild increase in turbulence in the inner part of the boundary layer. As the roughness increases above $k_{rms}^{+}\sim 1$, the flow over the SHSs transitions from drag reduction, where the viscous stress dominates, to drag increase where the Reynolds shear stress becomes the primary contributor. For the present maximum value of $k_{rms}^{+}=3.28$, the inner region exhibits the characteristics of a rough wall boundary layer, including elevated wall friction and turbulence as well as a downward shift in the mean velocity profile. Increasing the pressure in the test facility to a level that compresses the air layer on the SHSs and exposes the protruding roughness elements reduces the extent of drag reduction. Aligning the roughness elements in the streamwise direction increases the drag reduction. For SHSs where the roughness effect is not dominant ($k_{rms}^{+}<1$), the present measurements confirm previous theoretical predictions of the relationships between drag reduction and slip velocity, allowing for both spanwise and streamwise slip contributions.

The Ultimate Asymptote and Mean Flow Structure in Toms’ Phenomenon

1970 ◽  
Vol 37 (2) ◽  
pp. 488-493 ◽  
Author(s):  
P. S. Virk ◽  
H. S. Mickley ◽  
K. A. Smith
Keyword(s):  
Velocity Profile ◽  
Drag Reduction ◽  
Flow Structure ◽  
Viscous Sublayer ◽  
Mixing Length ◽  
Mean Flow ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
Length Constant ◽  
The Mean

The maximum drag reduction in turbulent pipe flow of dilute polymer solutions is ultimately limited by a unique asymptote described by the experimental correlation: f−1/2=19.0log10(NRef1/2)−32.4 The semilogarithmic mean velocity profile corresponding to and inferred from this ultimate asymptote has a mixing-length constant of 0.085 and shares a trisection (at y+ ∼ 12) with the Newtonian viscous sublayer and law of the wall. Experimental mean velocity profiles taken during drag reduction lie in the region bounded by the inferred ultimate profile and the Newtonian law of the wall. At low drag reductions the experimental profiles are well correlated by an “effective slip” model but this fails progressively with increasing drag reduction. Based on the foregoing a three-zone scheme is proposed to model the mean flow structure during drag reduction. In this the mean velocity profile segments are (a) a viscous sublayer, akin to Newtonian, (b) an interactive zone, characteristic of drag reduction, in which the ultimate profile is followed, and (c) a turbulent core in which the Newtonian mixing-length constant applies. The proposed model is consistent with experimental observations and reduces satisfactorily to the Taylor-Prandtl scheme and the ultimate profile, respectively, at the limits of zero and maximum drag reductions.

Experimental Investigations on Friction Drag Reduction on an Airfoil by Passive Blowing

2019 ◽  
Author(s):  
Shiho Hirokawa ◽  
Kaoruko Eto ◽  
Koji Fukagata ◽  
Naoko Tokugawa
Keyword(s):  
Drag Reduction ◽  
Leading Edge ◽  
Wing Surface ◽  
Experimental Investigations ◽  
Friction Drag ◽  
Mean Velocity ◽  
Local Reduction ◽  
Reduction Effect ◽  
Friction Drag Reduction ◽  
Suction And Blowing

Abstract Friction drag reduction effect of a passive blowing on a Clark-Y airfoil is investigated. The passive blowing is conducted by the pressure difference on a wing surface between suction and blowing regions. The suction and the blowing regions are respectively set around the leading edge and the rear part of the upper surface. The Reynolds number based on the chord length is 0.65 × 106 and 1.54 × 106. The angle of attack is set to 0° and 6°. The mean velocity profiles on the blowing region and the downstream are shifted away from the wall by the passive blowing. This behavior qualitatively suggests local reduction of skin friction on the wing surface. As a result of the quantitative assessment, which takes into account the effects of pressure gradient and the roughness of the wall, the local friction drag reduction effect of passive blowing is estimated to reach 4%–23%.

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