Numerical investigation of the effect of triangular cavity on the unsteady aerodynamics of NACA 0012 at a low Reynolds number

Abstract

Time accurate numerical simulations were conducted to investigate the effect of triangular cavities on the unsteady aerodynamic characteristics of NACA 0012 airfoil at a Reynolds number of 50,000. Right-angled triangular cavities are placed at 10%, 25% and 50% chord location on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The second-order accurate solution to the RANS equations is obtained using a pressure-based finite volume solver with a four-equation transition turbulence model, γ–Re_θt, to model the effect of turbulence. The two-dimensional results suggest that the cavity of depth 0.025c at 10% chord improves the aerodynamic efficiency (l/d ratio) by 52%, at an angle of attack of α = 8°, wherein the flow is steady. The shallower triangular cavity when placed at 25%c and 50%c enhances the l/d ratio by only 10% and 17%, respectively, in the steady-state regime of angles of attack between α = 6° and 10°. The deeper cavity also enhances the l/d ratio by up to 13%, 22% and 14% at angles of attack between α = 6° and 10°. Even in the unsteady vortex shedding regime, at α =12° and higher, significant improvements in the time-averaged l/d ratios are observed for both cavity depths. The improvements in l/d ratio in the steady-state, pre-stall regime are primarily because of drag reduction while in the post-stall, unsteady regime, the improvements are because of enhancements in time-averaged C_l values. The current finding can thus be used to enhance the aerodynamic performance of MAVs and UAVs that fly at low Reynolds numbers.

Keywords

Low Reynolds number NACA 0012 aerodynamic efficiency vortex shedding

Get full access to this article

View all access options for this article.

References

Lissaman

PBS

. Low-Reynolds-number airfoils. Annu. Rev. Fluid Mech 1983; 15: 223–239.

McKinney

DeLaurier

. The Wingmill: an oscillating-wing windmill. AIAA 80-0621R 1981; 5(2): 109–115.

Kinsey

Dumas

. Parametric study of an oscillating airfoil in a power-extraction regime. AIAA J 2008; 46(6): 1318–1330.

Xiao

Zhu

. A review on flow energy harvesters based on flapping foils. J Fluids Structures 2014; 46: 174–191.

Panaras

. Micro-vortex generators for shock wave/boundary layer interactions. Prog Aerospace Sci 2015; 74: 16–47.

Carmichael

. “Low Reynolds number Airfoil Survey,” NASA CR 165803. Washington, D.C, 1981.

Lin

JCM

Pauley

. Low-Reynolds-number separation on an airfoil. AIAA J 1996; 34(8): 1570–1577.

Yarusevych

Sullivan

Kawall

. On vortex shedding from an airfoil in low-Reynolds-number flows. J. Fluid Mech 2009; 632: 245–271.

Juanmian

Feng

Can

. Numerical study of separation on the trailing edge of a symmetrical airfoil at a low Reynolds number. Chin J Aeronautics 2013; 26(4): 918–925.

10.

Meara

MMO

Mueller

. Laminar separation bubble characteristics on an airfoil at low Reynolds numbers. AIAA J 1987; 25(8): 1033–1041.

11.

Kojima

Nonomura

Oyama

, et al. Large-Eddy simulation of low-Reynolds-number flow over thick and thin NACA airfoils. J Aircraft 2013; 50(1): 187–196.

12.

Yarusevych

Sullivan

Kawall

. Coherent structures in an airfoil boundary layer and wake at low Reynolds numbers. Phys Fluids 2006; 18: 044101, DOI: 10.1063/1.2187069.

13.

Marchman

III . Clark-Y airfoil performance at low Reynolds numbers. In: 22nd Aerospace sciences meeting, Reno, NV, 9–10 January 1984.

14.

Winslow

Otsuka

Govindarajan

et al. Basic understanding of airfoil characteristics at low Reynolds numbers (10⁴-10⁵). J Aircraft 2018; 53(3): 1050–1061, doi:10.2514/1.C034415.

15.

Alam

Zhou

Yang

, et al. The ultra-low Reynolds number airfoil wake. Exp Fluids 2010; 48: 81–103.

16.

Laitone

. Wind tunnel tests of wings at Reynolds numbers below 70 000. Exp Fluids 1997; 23: 405–409.

17.

Zhou

Alam

Yang

, et al. Fluid forces on a very low Reynolds number airfoil and their prediction. Int J Heat Fluid Flow 2011; 32: 329–339.

18.

Wang

Zhou

Alam

, et al. Turbulent intensity and Reynolds number effects on an airfoil at low Reynolds numbers. Phys Fluids 2014; 26(11): 115107–510725. DOI: 10.1063/1.4901969.

19.

Gad-el-Hak

Bushnell

. Separation control: review. J Fluids Eng 1991; 113(5).

20.

Bodavula

Yadav

Guven

. Numerical investigation of the unsteady aerodynamics of NACA0012 with suction surface protrusion. Aircraft Engineering and Aerospace Technology, 2019. (ahead-of-print). Accepted Manuscript.

21.

Bodavula

Yadav

Guven

. Stall mitigation and lift enhancement of NACA0012 with triangle shaped surface protrusion at a Reynolds Number of 10^5. SAE Int J Aerospace 2019; 12(2): 133–153.

22.

Kasper

. Aircraft Wing with Vortex Generation, 1974.U.S Patent No.3831885.

23.

Chernyshenko

Quinn

VortexCell . 6th EU framework programme for research and technological development(FP6), 2005-2009.

24.

Donelli

Iannelli

Iuliano

, et al. Suction optimization on thick airfoil to trap vortices. In: 19th AIMETA Italian association of theoretical and applied mechanics, Ancona, Italy, January, 2010, 1–10.

25.

Donelli

De Gregorio

Pierluigi

. Flow separation control by trapped vortex. In: 48th AIAA aerospace sciences meeting including the new horizons forum and aerospace exposition, Orlando, FL, January, 2010, 1–19.

26.

Gregorio

Fraioli

. Flow control on a high thickness airfoil by a trapped vortex cavity. 14th Int Symp Appl Laser Tech Fluid Mechanics 2012; 228(4): 557–566.

27.

Taherian

Nili-Ahmadabadi

Karimi

, et al. Flow visualization over a thick blunt trailing-edge airfoil with base cavity at low Reynolds numbers using PIV technique. J Visualization 2010; 20: 695–710.

28.

Olsman

JWF

Colonius

. Numerical simulation of flow over an airfoil with a cavity. AIAA J 2011; 49(1): 143–149.

29.

Zope

Janus

. Response surface analysis of trapped-vortex augmented airfoils. In: 31st AIAA applied aerodynamics conference, San Diego, CA, 24–27 June 2013.

30.

Gunasekaran

Gerham

. Effect of chordwise slots on aerodynamic efficiency and wingtip vortex. AIAA J 2018; 56: 1–16.

31.

Sutardi

Ching

. The response of a turbulent boundary layer to different shaped transverse grooves. Exp Fluids 2003; 35: 325–337.

32.

Duan

Zhao

, et al. Effect of airfoil concavity on wind turbine blade performances. Shock and Vibration 2019; 2019: 1–11.

33.

Liu

, et al. Numerical research on the turbulent drag reduction mechanism of a transverse groove structure on an airfoil blade. Eng Appl Comput Fluid Mech 2019; 13(1): 1024–1035.

34.

Liu

, et al. Numerical study of the effect of surface grooves on the aerodynamic performance of a NACA 4415 airfoil for small wind turbines. J Wind Eng Ind Aerodynamics 2020; 206: 104263.

35.

Seo

S-H

Hong

C-H

. Performance improvement of airfoils for wind blade with the groove. Int J Green Energ 2016; 13(1): 34–39.

36.

Menter

Langtry

Likki

, et al. A correlation-based transition model using local variables: part I — model formulation. Turbo Expo 2004; 4: 57–67.

37.

Menter

. Two-equation Eddy-viscosity turbulence models for engineering applications. AIAA J 1994; 32(8): 1598–1605.

38.

Ohtake

Nakae

Motohashi

. Nonlinearity of the aerodynamic characteristics of NACA0012 aerofoil at low Reynolds numbers. J Japan Society Aeronautical Space Sciences 2007; 55(644): 439–445.