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Journal ArticleDOI

Effect of Reynolds Number on Aerodynamics of Airfoil with Gurney Flap

21 Sep 2015-International Journal of Rotating Machinery (Hindawi)-Vol. 2015, Iss: 2015, pp 1-10

AbstractSteady 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.

Topics: Gurney flap (74%), Airfoil (60%), Angle of attack (60%), Lift coefficient (59%), NACA airfoil (58%)

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Citations
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Journal ArticleDOI
15 Nov 2019-Energy
Abstract: This paper presents a computational investigation on the effects of Gurney flaps on the aerodynamic performance of a horizontal axis wind turbine, which is part of the EU FP7 AVATAR project. The research investigates two configurations of Gurney flaps applied at the inboard part of the blade ( r / R = 0.30 ∼ 0.46 ) at 85 % chord location on the pressure surface. The computational method applied in the investigation solves the Reynold-Averaged Navier-Stokes (RANS) equations with multiple reference frame (MRF) approach, which models the rotating turbulent flow over the wind turbine rotor. Numerical simulations are performed for the wind turbine rotor with and without Gurney flap at the tip speed ratios λ = 4.59 and 6.35. Comparison of the numerical results with experimental measurements shows that the deployment of Gurney flaps effectively increases the power coefficients of the rotor by 21 % at λ = 6.35 . Gurney flaps have a considerable 3D effect on spanwise thrust and torque coefficients distribution. The performance of two Gurney flaps configurations is compared. It is shown that the larger Gurney flap reduces the effect on the power generated due to protruding out of the local boundary layer of the flow. The numerical results are in good agreement with the experimental results in terms of total thrust and power within 14.1 % difference, and complement the experimental database.

9 citations


Journal ArticleDOI
Abstract: The flow characteristics and the lift and drag behavior of a thick trailing-edged airfoil that was provided with fixed trailing edge flaps (Gurney flaps) of 1% to 5% height right at the back of the airfoil were studied both experimentally and numerically at different low Reynolds numbers (Re) and angles of attack for possible applications in wind turbines suitable for the wind speeds of 4-6 m/s. The flap considerably improves the suction on the upper surface of the airfoil resulting in a higher lift coefficient. The drag coefficient also increased; however, the increase was less compared to the increase in the lift coefficient, resulting in a higher lift-to-drag ratio in the angles of attack of interest. The results show that trailing-edge flaps can improve the performance of blades designed for low wind speeds and can directly be applied to small wind turbines that are increasingly being used in remote places or in smaller countries.

4 citations



Proceedings ArticleDOI
01 Sep 2020
Abstract: The increasing demand of UAS has generated interest in the scientific community to understand how the environmental parameters affect performance of these emerging vehicles. A bias in the existing tests has been the non-reproducibility of the same climatic conditions. Therefore, UAS have not been fully exploited by the marker so far. Standard protocols for UAS testing in unconventional weather conditions have not been investigated from both industry and academic research. Temperature and pressure are environmental parameters that affect the aerodynamics of Unmanned Aircraft Systems (UAS). Low Reynolds numbers are common for small scale UAS and have a strongly influence on propeller and vehicle capabilities. In the past years, experimental studies on the effects of low Reynolds numbers have been carried out in wind tunnel facilities in conventional atmospheres (ambient temperature and pressure). Moreover, the complexity of the aerodynamic field results in propeller and full vehicle performance prediction methods with limited accuracy. In this paper an experimental setup inside a climatic and hypobaric laboratory is used to highlight temperature and pressure influence on single propeller and full vehicle performance in static conditions (hover). Test results are discussed and provided to the reader, highlighting the complexities of the measurements when extreme temperature and low pressure are set. The main contribution of this study is a set of experimental data to pave the way for a deep investigation on harsh environmental conditions on UAS propulsion system.

2 citations


Cites background from "Effect of Reynolds Number on Aerody..."

  • ...The study performed by [24] on the effect of Reynolds number on airfoils shows that low Reynolds usually result in smaller lift and increased drag coefficients....

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Proceedings ArticleDOI
15 Jun 2020

2 citations


Cites result from "Effect of Reynolds Number on Aerody..."

  • ...This observation has also been mentioned in other papers [7]....

    [...]


References
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Journal ArticleDOI
Abstract: To calculate complex turbulent flows with separation and heat transfer, we have developed a new turbulence model for flow field, which is modified from the latest low-Reynolds-number k−g3 model. The main improvement is achieved by the introduction of the Kolmogorov velocity scale, uc Z (ve) 1 4 , instead of the friction velocity uτ, to account for the near-wall and low-Reynolds-number effects in both attached and detached flows. The present model predicts quite successfully the separating and reattaching flows downstream of a backward-facing step, which involve most of the essential physics of complex turbulent flows, under various flow conditions. We have also discussed in detail the structure of the separating and reattaching flow based on the computational results, and presented several important features closely related to the mechanism of turbulent heat transfer.

658 citations


Journal ArticleDOI
Abstract: Nomenclature c = airfoil chord CL = lift coefficient = L/!/2pV00c CLu = upper-surface lift coefficient Cp = pressure coefficient = (p -p^)/ Ap Vx 2 Mx = freestream Mach number p = static pressure Re^ = freestream Reynolds number based on airfoil chord = V^clv sp = location of leading-edge stagnation point V^ — freestream velocity v local velocity on airfoil surface x = distance along chord line F = circulation about the airfoil 7 = ratio of specific heats v = kinematic viscosity p = density () oo = freestream conditions () t e = conditions at the airfoil trailing edge

489 citations


"Effect of Reynolds Number on Aerody..." refers background in this paper

  • ...A recirculating vortex that occurs just upstream of Gurney flap may be the reason for this adverse pressure gradient [2]....

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Journal ArticleDOI
Abstract: The laminar separation, transition, and turbulent reattachment near the leading edge of a two-dimensional NACA 663 -018 airfoil were investigated using a low-speed, smoke visualization wind tunnel. Lift and drag force measurements were made using an external strain gage balance for a chord Reynolds number range of 40,GOO400,000. An extensive flow visualization study was performed and correlated with the force measurements. Experiments were also conducted with distributed surface roughness at the leading edge and external acoustic excitation to influence the development of the airfoil boundary layer. This study delineates the effects of angle of attack and chord Reynolds number on the separation characteristics and airfoil performance. Nomenclature c = model chord cd = section profile drag coefficient (uncorrected) cf = section lift coefficient (uncorrected) Cp = pressure coefficient / = acoustic frequency, Hz R = reattachment location Rc = Reynolds number based on chord length, U^ civ S = separation location T = location of approximate end of transition £/«, = freestream velocity x/c = nondimensional distance along chord a = angle of attack v - kinematic viscosity

231 citations


Book
01 Jan 1989

163 citations


"Effect of Reynolds Number on Aerody..." refers background in this paper

  • ...[6], Brown and Filippone [7], and Traub and Agarwal [8] have studied the performance of airfoils at low Reynolds numbers but a systematic investigation is still not available....

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