The Effect of Bionic 3D Printed Structure Morphology on Skin Friction

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Zhang Zhihao ◽  
Ito Makoto ◽  
Wang Xishu ◽  
Liu Jinsheng
Keyword(s):  
Skin Friction ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Flow Conditions ◽  
Additive Manufacturing Technology ◽  
Dragonfly Wing ◽  
Structure Morphology ◽  
3D Printed ◽  
Coefficient Versus

Abstract Dragonfly has remarkable flight efficiency, with unique wing structural properties such as the surface topological vein structures, corrugation, etc. The object of this paper is to identify how the polygonal patterns of the samples with bionic wing veins affected the skin friction. Four kinds of polygonal three-dimensional (3D) patterns were designed and fabricated by additive manufacturing technology, and the skin friction coefficients (Cf) of various models were measured by the wind channel experiments. The quantitative effects of models on Cf with different Reynolds numbers (Re) in laminar, transitional, and turbulent flow conditions were obtained. Results indicated that the law of whole change of the skin friction coefficient versus Re is the same for all patterns which can be expressed by an empirical formula Cf=kReα. The model with mixed square and pentagonal patterns always generates the highest skin friction in the different flow conditions, which was speculated to play an important role on the attenuation of the flow separation of the dragonfly wing.

Low-Reynolds-Number Turbulent Boundary Layers in Zero and Favorable Pressure Gradients

1983 ◽  
Vol 27 (03) ◽  
pp. 147-157 ◽  
Author(s):  
A. J. Smits ◽  
N. Matheson ◽  
P. N. Joubert
Keyword(s):  
Friction Coefficient ◽  
Skin Friction ◽  
Boundary Layers ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Turbulent Boundary Layers ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Low Reynolds

This paper reports the results of an extensive experimental investigation into the mean flow properties of turbulent boundary layers with momentum-thickness Reynolds numbers less than 3000. Zero pressure gradient and favorable pressure gradients were studied. The velocity profiles displayed a logarithmic region even at very low Reynolds numbers (as low as Rθ = 261). The results were independent of the leading-edge shape, and the pin-type turbulent stimulators performed well. It was found that the shape and Clauser parameters were a little higher than the correlation proposed by Coles [10], and the skin friction coefficient was a little lower. The skin friction coefficient behavior could be fitted well by a simple power-law relationship in both zero and favorable pressure gradients.

Control of Separated Boundary-Layer on Subsonic Airfoil Using Vortex Generator Jet Devices

2006 ◽  
Author(s):  
A. Kourta ◽  
G. Petit ◽  
J. C. Courty ◽  
J. P. Rosenblum
Keyword(s):  
Boundary Layer ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Three Dimensional ◽  
Vortex Generator ◽  
Leading Edge ◽  
Skin Friction Coefficient ◽  
Synthetic Jets ◽  
High Lift ◽  
Longitudinal Vortices

The control of subsonic high lift induced separation on airfoil may improve the flight envelope of current aircraft or even simplify the complex and heavy high-lift devices on commercial airframes. Until now, synthetic jets have proved a really interesting efficiency to delay or remove even leading-edge located separated areas on high-lift configuration but are not efficient for real scale aircrafts. In case of pressure-like separation (i.e. from trailing-edge), synthetic jets can be replaced by so the called “Vortex Generator Jets” which create strong longitudinal vortices that increase mixing in inner boundary layer and consequently the skin friction coefficient is increased to prevent separation. In this study, numerical simulations were undertaken on a generic three dimensional flat plate in order to quantify the effect of the longitudinal vortices on the natural skin friction coefficient. Both counter and co-rotative devices were tested at different exhaust velocities and distances between each others. Finally co-rotative vortex generators jets were tested on a three dimensional generic airfoil ONERA D. Results show a delay of the separation occurence but this solution does not seem to be as robust as synthetic jets. The study of jets spacing with respect to the efficiency of the devices shows a maximum for a given ratio of spacing to exhaust velocity.

scholarly journals Darcy–Forchheimer flow of micropolar nanofluid between two plates in the rotating frame with non-uniform heat generation/absorption

2018 ◽  
Vol 10 (10) ◽  
pp. 168781401880885 ◽  
Author(s):  
Arshad Khan ◽  
Zahir Shah ◽  
Saeed Islam ◽  
Sajad Khan ◽  
Waris Khan ◽  
...  
Keyword(s):  
Skin Friction ◽  
Transverse Velocity ◽  
Three Dimensional ◽  
Skin Friction Coefficient ◽  
Porous Space ◽  
Strong Concentration ◽  
Permeable Media ◽  
Micropolar Nanofluid ◽  
Flow Motion ◽  
Forchheimer Flow

This article studies the Darcy–Forchheimer flow of three-dimensional micropolar nanofluid between parallel and horizontal plates in a rotating system. The micropolar nanofluid in permeable media is described by assuming the Darcy–Forchheimer model, where drenching the permeable space obeys the Darcy–Forchheimer expression. The significant influence of Brownian motion and thermophoresis has been taken in the nanofluids model. The thermal radiation impact is taken to be varying in terms of non-uniform absorption/generation for the purpose to see the concentration as well as the temperature modifications between the nanofluid and the surfaces. The leading equations are converted into a system of differential nonlinear equations and then homotopic method is used for solving the modeled equations. The other physical impacts, that is, skin friction, heat flux, and mass flux, have been studied through tables. The impacts of the porosity, rotation, and inertia coefficient analysis have been mainly focused in this research. It is observed that the higher value of Fr decay the velocity profile, while it increases the transverse velocity, and the increase in the porosity parameter [Formula: see text] increases the porous space, which creates resistance in the flow path and reduces the flow motion. Skin friction coefficient is observed to be larger for the strong concentration [Formula: see text], as compared to the case of weak concentration [Formula: see text]. Impact of strong and weak concentrations on Nusselt and Sherwood numbers seems to be similar in a quantitative sense.

Incipient stall characterization from skin-friction maps

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Massimo Miozzi ◽  
Alessandro Capone ◽  
Christian Klein ◽  
Marco Costantini
Keyword(s):  
Skin Friction ◽  
Vector Fields ◽  
Three Dimensional ◽  
Suction Side ◽  
Temperature Sensitive ◽  
Flow Conditions ◽  
Time Resolved ◽  
Content Type ◽  
Fundamental Information ◽  
Taylor Hypothesis

Purpose The purpose of this study is the characterization of the dramatic variation in the flow scenario occurring at incipient stall conditions on a NACA0015 hydrofoil at moderate Reynolds numbers via the experimental analysis of time- and space-resolved skin-friction maps. The examined flow conditions are relevant for a variety of applications, including renewable energy production and unmanned and micro-aerial vehicles. Design/methodology/approach Grounding on the global temperature data acquired via temperature-sensitive paint, the proposed methodology adopts two approaches: one to obtain time-resolved, relative skin-friction vector fields by means of an optical-flow-based algorithm and the other one to extract quantitative, time-averaged skin-friction maps after minimization of the dissimilarity between the observed passive transport of temperature fluctuations and that suggested by the Taylor hypothesis. Findings Through the synergistic application of the proposed methods, the time-dependent evolution of the incipient stall over the hydrofoil suction side is globally described by firstly identifying the trailing edge separation at an angle of attack (AoA) AoA = 11.5°, and then by capturing the onset of upstream oriented, mushroom-like structures at AoA = 13°. The concomitant occurrence of both scenarios is found at the intermediate incidence AoA = 12.2°. Originality/value The qualitative, time-resolved skin-friction topology, combined with the quantitative, time-averaged distribution of the streamwise friction velocity, enables to establish a portrait of the complex, three-dimensional, unsteady scenario occurring at the examined flow conditions, thus providing new, fundamental information for a deeper understanding of the incipient stall development and for its control.

scholarly journals Three-Dimensional Flow and Heat Transfer Past a Permeable Exponentially Stretching/Shrinking Sheet in a Nanofluid

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
Syahira Mansur ◽  
Anuar Ishak ◽  
Ioan Pop
Keyword(s):  
Nusselt Number ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Local Nusselt Number ◽  
Three Dimensional ◽  
Lewis Number ◽  
Skin Friction Coefficient ◽  
Shrinking Sheet ◽  
Three Dimensional Flow ◽  
Flow And Heat Transfer

The three-dimensional flow and heat transfer of a nanofluid over a stretching/shrinking sheet is investigated. Numerical results are obtained using bvp4c in MATLAB. The results show nonunique solutions for the shrinking case. The effects of the stretching/shrinking parameter, suction parameter, Brownian motion parameter, thermophoresis parameter, and Lewis number on the local skin friction coefficient and the local Nusselt number are studied. Suction increases the solution domain. Furthermore, as the sheet is shrunk in thex-direction, suction increases the skin friction coefficient in the same direction while decreasing the skin friction coefficient in they-direction. The local Nusselt number is consistently lower for higher values of thermophoresis parameter and Lewis number. On the other hand, the local Nusselt number increases as the Brownian motion parameter increases.

Thermal Slip Flow of a Three-Dimensional Casson Fluid Embedded in a Porous Medium with Internal Heat Generation

2021 ◽  
Vol 10 (1) ◽  
pp. 58-66
Author(s):  
K. Gangadhar ◽  
M. Venkata Subba Rao ◽  
K. Venkata Ramana ◽  
Ch. Suresh Kumar ◽  
Ali J. Chamkha
Keyword(s):  
Skin Friction ◽  
Slip Flow ◽  
Three Dimensional ◽  
Internal Heat ◽  
Relaxation Method ◽  
Casson Fluid ◽  
Skin Friction Coefficient ◽  
Newtonian Case ◽  
Spectral Relaxation Method ◽  
Spectral Relaxation

Present assessment is considered to analysis flow as well as heat characteristics of steady, thermal slip flow of three-dimensional Casson fluid embedded in a porous medium with internal heat generation. Geometry of the present analysis is linearly stretched surface. Later, all the PDEs corresponding to the study are altered to set of nonlinear equations ODEs by means of appropriate similarity transformations. An efficient numerical scheme of spectral relaxation method (SRM) is applied to solve the nonlinear ordinary system. Variations of Nusselt number, temperature, velocity, and local skin friction coefficient with fluid parameters exhibited by graphs and tables. Spectral relaxation method gives an exact convergence to the nonlinear boundary value problems compare with general methods. In this study, to improve the precision and accuracy of the SRM successive over-relaxation (SOR) strategy is utilized. Proposed method as well as outcomes is checked with the comparison. A sensible connection is acquired between the current outcomes and accessible outcomes in writing. Some of the observations are skin friction coefficient raises and velocities decreases by the magnetic field strength. Skin friction and Local Nusselt number at the surface is more pronounced for non-Newtonian case than that of Newtonian case.

Characteristics of Flow around a Modified Square Prism

2015 ◽  
Vol 723 ◽  
pp. 190-193
Author(s):  
Lin Zou ◽  
Yong Hu ◽  
Han Bin Xu ◽  
Hong Lu ◽  
Miao Wang
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Flow Induced Vibration ◽  
Near Wake ◽  
Piv Measurements ◽  
Square Prism ◽  
Free Shear Layers ◽  
Force Reduction ◽  
Sinusoidal Surface

The present investigations focus attention on PIV measurements and three-dimensional numerical investigation on flow past a modified square prism with a sinusoidal surface. The detailed near wake vortex structures and velocity fields of such modified square prism are captured and compared with a straight square prism in the same flow conditions. The three-dimensional free shear layers behind the modified square prism extend further downstream and become more stable than those of the straight one. For a modified square prism, significant mean drag coefficient reduction and fluctuating lift suppression are obtained at the Reynolds numbers of 600 and 5900. It indicates that such modified square prism is capable of minimization of flow induced vibration and force reduction.

scholarly journals Control of vortex shedding on two- and three-dimensional aerofoils

2011 ◽  
Vol 369 (1940) ◽  
pp. 1525-1539 ◽  
Author(s):  
Tim Colonius ◽  
David R. Williams
Keyword(s):  
Vortex Shedding ◽  
Flight Control ◽  
Three Dimensional ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Separated Flows ◽  
Flow Conditions ◽  
Flat Plates ◽  
Low Reynolds Numbers

We review and expand on the control of separated flows over flat plates and aerofoils at low Reynolds numbers associated with micro air vehicles. Experimental observations of the steady-state and transient lift response to actuation, and its dependence on the actuator, aerofoil geometry and flow conditions, are discussed and an attempt is made to unify them in terms of their excitation of periodic and transient vortex shedding. We also examine strategies for closed-loop flow and flight control using actuation of leading-edge vortices.

scholarly journals Unsteady MHD Mixed Convection Flow in Hybrid Nanofluid at Three-Dimensional Stagnation Point

Mathematics ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 549
Author(s):  
Nurul Amira Zainal ◽  
Roslinda Nazar ◽  
Kohilavani Naganthran ◽  
Ioan Pop
Keyword(s):  
Heat Transfer ◽  
Friction Coefficient ◽  
Differential Equations ◽  
Mixed Convection ◽  
Skin Friction ◽  
Stagnation Point ◽  
Three Dimensional ◽  
Skin Friction Coefficient ◽  
Stagnation Point Flow ◽  
Hybrid Nanofluid

There has been significant interest in exploring a stagnation point flow due to its numerous potential uses in engineering applications such as cooling of nuclear reactors. Hence, this study proposed a numerical analysis on the unsteady magnetohydrodynamic (MHD) mixed convection at three-dimensional stagnation point flow in Al2O3–Cu/H2O hybrid nanofluid over a permeable sheet. The ordinary differential equations are accomplished by simplifying the governing partial differential equations through suitable similarity transformation. The numerical computation is established by the MATLAB system software using the bvp4c technique. The bvp4c procedure is excellent in providing more than one solution once sufficient predictions are visible. The influence of certain functioning parameters is inspected, and notable results exposed that the rate of heat transfer is exaggerated along with the skin friction coefficient while the suction/injection and magnetic parameters are intensified. The results also signified that the rise in the volume fraction of the nanoparticle and the decline of the unsteadiness parameter demonstrates a downward attribution towards the heat transfer performance and skin friction coefficient. Conclusively, the observations are confirmed to have multiple solutions, which eventually contribute to an investigation of the analysis of the solution stability, thereby justifying the viability of the first solution.

A theoretical decomposition of mean skin friction generation into physical phenomena across the boundary layer

2016 ◽  
Vol 790 ◽  
pp. 339-367 ◽  
Author(s):  
Nicolas Renard ◽  
Sébastien Deck
Keyword(s):  
Boundary Layer ◽  
Skin Friction ◽  
Reynolds Shear Stress ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Momentum Budget ◽  
The Mean ◽  
Logarithmic Layer ◽  
High Reynolds ◽  
Physical Phenomena

A theoretical decomposition of mean skin friction generation into physical phenomena across the whole profile of the incompressible zero-pressure-gradient smooth-flat-plate boundary layer is derived from a mean streamwise kinetic-energy budget in an absolute reference frame (in which the undisturbed fluid is not moving). The Reynolds-number dependences in the laminar and turbulent cases are investigated from direct numerical simulation datasets and Reynolds-averaged Navier–Stokes simulations, and the asymptotic trends are consistently predicted by theory. The generation of the difference between the mean friction in the turbulent and laminar cases is identified with the total production of turbulent kinetic energy (TKE) in the boundary layer, represented by the second term of the proposed decomposition of the mean skin friction coefficient. In contrast, the analysis introduced by Fukagataet al.(Phys. Fluids, vol. 14 (11), 2002, pp. 73–76), based on a streamwise momentum budget in the wall reference frame, relates the turbulence-induced excess friction to the Reynolds shear stress weighted by a linear function of the wall distance. The wall-normal distribution of the linearly-weighted Reynolds shear stress differs from the distribution of TKE production involved in the present discussion, which consequently draws different conclusions on the contribution of each layer to the mean skin friction coefficient. At low Reynolds numbers, the importance of the buffer-layer dynamics is confirmed. At high Reynolds numbers, the present decomposition quantitatively shows for the first time that the generation of the turbulence-induced excess friction is dominated by the logarithmic layer. This is caused by the well-known decay of the relative contributions of the buffer layer and wake region to TKE production with increasing Reynolds numbers. This result on mean skin friction, with a physical interpretation relying on an energy budget, is consistent with the well-established general importance of the logarithmic layer at high Reynolds numbers, contrary to the friction breakdown obtained from the approach of Fukagataet al.(Phys. Fluids, vol. 14 (11), 2002, pp. 73–76), essentially based on a momentum budget. The new decomposition suggests that it may be worth investigating new drag reduction strategies focusing on TKE production and on the nature of the logarithmic layer dynamics. The decomposition is finally extended to the pressure-gradient case and to channel and pipe flows.

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