Experimental study of low Reynolds number effects on aerodynamics of smooth and sinusoidal leading-edge wings in the vicinity of the ground

Present study experimentally investigates the effects of ground clearance and Reynolds number on aerodynamic coefficients of smooth and sinusoidal leading-edge wings. Wind tunnel tests are conducted over a wide range of angles of attack from zero to 36 degrees, low Reynolds numbers of 30,000, 45,000 and 60,000, and also ground clearances of 0.5, 1 and ∞. Results showed that reduction of ground clearance and increment of Reynolds number cause the lift coefficient and the lift to drag ratio of both wings to be enhanced. Furthermore, the effects of Reynolds number and ground clearance on the smooth leading-edge wing are more than the sinusoidal leading-edge one. In addition, the sinusoidal leading-edge wing shows an excellent performance in the poststall region due to producing a higher lift and also by delaying the stall angle compared to the smooth leading-edge wing.

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Low Reynolds number flow around and heat transfer from a heated circular cylinder

International Review of Applied Sciences and Engineering ◽

10.1556/irase.1.2010.1-2.3 ◽

2010 ◽

Vol 1 (1-2) ◽

pp. 15-20 ◽

Cited By ~ 1

Author(s):

B. Bolló

Keyword(s):

Reynolds Number ◽

Circular Cylinder ◽

Lift Coefficient ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Reynolds Number Flow ◽

Two Dimensional Flow ◽

Number Flow ◽

Low Reynolds ◽

Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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Experimental Aerodynamic Characteristics of a Compound Wing in Ground Effect

Journal of Fluids Engineering ◽

10.1115/1.4026618 ◽

2014 ◽

Vol 136 (5) ◽

Cited By ~ 2

Author(s):

Saeed Jamei ◽

Adi Maimun Abdul Malek ◽

Shuhaimi Mansor ◽

Nor Azwadi Che Sidik ◽

Agoes Priyanto

Keyword(s):

Reynolds Number ◽

Drag Coefficient ◽

Center Of Pressure ◽

Lift Coefficient ◽

Angle Of Attack ◽

Leading Edge ◽

Ground Effect ◽

Reynolds Numbers ◽

Aerodynamic Characteristics ◽

Ground Clearance

Wing configuration is a parameter that affects the performance of wing-in-ground effect (WIG) craft. In this study, the aerodynamic characteristics of a new compound wing were investigated during ground effect. The compound wing was divided into three parts with a rectangular wing in the middle and two reverse taper wings with anhedral angle at the sides. The sectional profile of the wing model is NACA6409. The experiments on the compound wing and the rectangular wing were carried to examine different ground clearances, angles of attack, and Reynolds numbers. The aerodynamic coefficients of the compound wing were compared with those of the rectangular wing, which had an acceptable increase in its lift coefficient at small ground clearances, and its drag coefficient decreased compared to rectangular wing at a wide range of ground clearances, angles of attack, and Reynolds numbers. Furthermore, the lift to drag ratio of the compound wing improved considerably at small ground clearances. However, this improvement decreased at higher ground clearance. The drag polar of the compound wing showed the increment of lift coefficient versus drag coefficient was higher especially at small ground clearances. The Reynolds number had a gradual effect on lift and drag coefficients and also lift to drag of both wings. Generally, the nose down pitching moment of the compound wing was found smaller, but it was greater at high angle of attack and Reynolds number for all ground clearance. The center of pressure was closer to the leading edge of the wing in contrast to the rectangular wing. However, the center of pressure of the compound wing was later to the leading edge at high ground clearance, angle of attack, and Reynolds number.

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Effect of Reynolds Number on Aerodynamics of Airfoil with Gurney Flap

International Journal of Rotating Machinery ◽

10.1155/2015/628632 ◽

2015 ◽

Vol 2015 ◽

pp. 1-10 ◽

Cited By ~ 5

Author(s):

Shubham Jain ◽

Nekkanti Sitaram ◽

Sriram Krishnaswamy

Keyword(s):

Reynolds Number ◽

Lift Coefficient ◽

Angle Of Attack ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Critical Range ◽

Gurney Flap ◽

Stall Angle ◽

Lift And Drag ◽

Naca 0012

Steady state, two-dimensional computational investigations performed on NACA 0012 airfoil to analyze the effect of variation in Reynolds number on the aerodynamics of the airfoil without and with a Gurney flap of height of 3% chord are presented in this paper. RANS based one-equation Spalart-Allmaras model is used for the computations. Both lift and drag coefficients increase with Gurney flap compared to those without Gurney flap at all Reynolds numbers at all angles of attack. The zero lift angle of attack seems to become more negative as Reynolds number increases due to effective increase of the airfoil camber. However the stall angle of attack decreased by 2° for the airfoil with Gurney flap. Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers.

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A Study on Reynolds Number Effects in Turbomachines

Journal of Engineering for Power ◽

10.1115/1.3677584 ◽

1964 ◽

Vol 86 (3) ◽

pp. 227-235 ◽

Cited By ~ 16

Author(s):

O. E. Balje´

Keyword(s):

Reynolds Number ◽

Test Data ◽

Pressure Ratio ◽

Reynolds Numbers ◽

Fair Agreement ◽

Low Reynolds Numbers ◽

Reynolds Number Effects ◽

Comprehensive Test ◽

Specific Speed ◽

Low Reynolds

Typical space power units have a tendency to encounter low Reynolds numbers in the last turbine stages. Comprehensive test data on the effect of low Reynolds numbers on the efficiency of turbomachines are lacking. An attempt is made to assess this influence, using conventional aerodynamic arguments. By distinguishing between viscous and nonviscous losses some tentative values have been calculated which are in fair agreement with the few available test data. These considerations indicate that the stage pressure ratio and the specific speed affect the Reynolds number influence significantly.

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Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410020946903 ◽

2020 ◽

pp. 095441002094690

Author(s):

AA Mehraban ◽

MH Djavareshkian ◽

Y Sayegh ◽

B Forouzi Feshalami ◽

Y Azargoon ◽

...

Keyword(s):

High Performance ◽

Leading Edge ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Drag Forces ◽

Wide Range ◽

Beam Bending ◽

Low Reynolds ◽

Lift And Drag ◽

Drag Ratio

Sinusoidal leading-edge wings have shown a high performance after the stall region. In this study, the role of smart flaps in the aerodynamics of smooth and sinusoidal leading-edge wings at low Reynolds numbers of 29,000, 40,000 and 58,000 is investigated. Four wings with NACA 634-021 profile are firstly designed and then manufactured by a 3 D printer. Beam bending equation is used to determine the smart flap chord deflection. Next, wind tunnel tests are carried out to measure the lift and drag forces of proposed wings for a wide range of angles of attack, from zero to 36 degrees. Results show that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap. However, a combination of smooth leading-edge wing and smart flap advances the stall. Furthermore, it is found that wings with smart flap generally have a higher lift to drag ratio due to their excellent performance in producing lift.

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Turbulent intensity and Reynolds number effects on an airfoil at low Reynolds numbers

Physics of Fluids ◽

10.1063/1.4901969 ◽

2014 ◽

Vol 26 (11) ◽

pp. 115107 ◽

Cited By ~ 48

Author(s):

S. Wang ◽

Y. Zhou ◽

Md. Mahbub Alam ◽

H. Yang

Keyword(s):

Reynolds Number ◽

Reynolds Numbers ◽

Turbulent Intensity ◽

Low Reynolds Numbers ◽

Reynolds Number Effects ◽

Low Reynolds

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Low-Reynolds-number effects in a fully developed turbulent channel flow

Journal of Fluid Mechanics ◽

10.1017/s002211209200154x ◽

1992 ◽

Vol 236 ◽

pp. 579-605 ◽

Cited By ~ 165

Author(s):

R. A. Antonia ◽

M. Teitel ◽

J. Kim ◽

L. W. B. Browne

Keyword(s):

Reynolds Number ◽

Channel Flow ◽

Low Reynolds Number ◽

Turbulent Channel Flow ◽

Reynolds Numbers ◽

Wall Region ◽

Low Reynolds Numbers ◽

Reynolds Number Effects ◽

Low Reynolds ◽

Inner Region

Low-Reynolds-number effects are observed in the inner region of a fully developed turbulent channel flow, using data obtained either from experiments or by direct numerical simulations. The Reynolds-number influence is observed on the turbulence intensities and to a lesser degree on the average production and dissipation of the turbulent energy. In the near-wall region, the data confirm Wei & Willmarth's (1989) conclusion that the Reynolds stresses do not scale on wall variables. One of the reasons proposed by these authors to account for this behaviour, namely the ‘geometry’ effect or direct interaction between inner regions on opposite walls, was investigated in some detail by introducing temperature at one of the walls, both in experiment and simulation. Although the extent of penetration of thermal excursions into the opposite side of the channel can be significant at low Reynolds numbers, the contribution these excursions make to the Reynolds shear stress and the spanwise vorticity in the opposite wall region is negligible. In the inner region, spectra and co-spectra of the velocity fluctuations u and v change rapidly with the Reynolds number, the variations being mainly confined to low wavenumbers in the u spectrum. These spectra, and the corresponding variances, are discussed in the context of the active/inactive motion concept and the possibility of increased vortex stretching at the wall. A comparison is made between the channel and the boundary layer at low Reynolds numbers.

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Experiments on the Velocity Field Around a Low Aspect Ratio Wing at Low Reynolds Numbers

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-13172 ◽

2009 ◽

Author(s):

Daniel R. Morse ◽

James A. Liburdy

Keyword(s):

Reynolds Number ◽

Aspect Ratio ◽

Leading Edge ◽

Reynolds Numbers ◽

Shear Stresses ◽

Tip Vortices ◽

Low Reynolds Numbers ◽

Low Aspect Ratio ◽

Low Reynolds ◽

Wing Tip

The flow structure around a low aspect ratio wing at low Reynolds numbers and a fixed angle of attack of 20° is discussed using flow visualization as well as Three-Component Time-Resolved Particle Image Velocimetry (3C TR PIV). Mean quantities and statistical measurements of velocity were obtained and used to describe the average and transient characteristics of the flow field. Effects of spanwise variation from centerline to wingtip and Reynolds number variation from 1.3×104 to 6.6×104 are discussed. The role of the wing tip vortices is observed to be large in a low aspect ratio wing. The transfer of momentum via Reynolds shear stresses is shown in the leading edge region. Normalized spanwise shear stresses associated with the wing tip vortices are observed to increase with increasing Reynolds number.

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Effects of Free Stream Turbulence on Low Reynolds Number Boundary Layers

Journal of Fluids Engineering ◽

10.1115/1.3243119 ◽

1984 ◽

Vol 106 (3) ◽

pp. 298-306 ◽

Cited By ~ 44

Author(s):

I. P. Castro

Keyword(s):

Reynolds Number ◽

Boundary Layers ◽

Free Stream ◽

Reynolds Numbers ◽

Length Scale ◽

Mean Flow ◽

Low Reynolds Numbers ◽

Free Stream Turbulence ◽

Reynolds Number Effects ◽

Low Reynolds

This paper documents some of the effects of free stream turbulence on the mean flow properties of turbulent boundary layers in zero pressure gradients. Attention is concentrated on flows for which the momentum thickness Reynolds number is less than about 2000. Direct Reynolds number effects are therefore significant and it is shown that such effects reduce as the level of free stream turbulence rises. A modification to Hancock’s [1] empirical correlation relating the fractional increase in skin friction at constant Reynolds number to a free stream turbulence parameter containing a dependence on both intensity and length scale is proposed. While this modification has the necessary characteristic of being a function of the free stream turbulence parameters as well as the Reynolds number, it is argued that the relative importance of intensity and length scale changes at low Reynolds numbers; the data are not inconsistent with this idea. The experiments cover the range 500 ⪝ Reθ ⪝ 2500, u′/Ue ⪝ 0.07, 0.8 ⪝ Le/δ ⪝ 2.9, where u′/Ue is the free stream turbulence intensity and Le/δ is the ratio of the dissipation length scale of the free stream turbulence to the 99 percent thickness of the boundary layer.

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