Large-Eddy Simulation of Low-Reynolds-Number Flow Over Thick and Thin NACA Airfoils

Kojima, Ryoji; Nonomura, Taku; Oyama, Akira; Fujii, Kozo

doi:10.2514/1.c031849

Cited by 83 publications

(51 citation statements)

References 17 publications

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“…Refs. [6][7][8]. Therefore, a better understanding of the LSB characteristics is essential to prevent the unintended degradation of performance due to the LSB.…”

Section: Introductionmentioning

confidence: 98%

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

et al. 2015

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Mechanisms behind the pressure distribution and skin friction within a laminar separation bubble (LSB) are investigated by large-eddy simulations around a 5% thickness blunt flat plate at the chord length based Reynolds number 5.0 × 103, 6.1 × 103, 1.1 × 104, and 2.0 × 104. The characteristics inside the LSB change with the Reynolds number; a steady laminar separation bubble (LSB_S) at the Reynolds number 5.0 × 103 and 6.1 × 103, and a steady-fluctuating laminar separation bubble (LSB_SF) at the Reynolds number 1.1 × 104, and 2.0 × 104. Different characteristics of pressure and skin friction distributions are observed by increasing the Reynolds number, such that a gradual monotonous pressure recovery in the LSB_S and a plateau pressure distribution followed by a rapid pressure recovery region in the LSB_SF. The reasons behind the different characteristics of pressure distributions at different Reynolds numbers are discussed by deriving the Reynolds averaged pressure gradient equation. It is confirmed that the viscous stress distributions near the surface play an important role in determining the formation of different pressure distributions. Depending on the Reynolds numbers, the viscous stress distributions near the surface are affected by the development of a separated laminar shear layer or the Reynolds shear stress. In addition, we show that the same analyses can be applied to the flows around a NACA0012 airfoil.

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“…Refs. [6][7][8]. Therefore, a better understanding of the LSB characteristics is essential to prevent the unintended degradation of performance due to the LSB.…”

Section: Introductionmentioning

confidence: 98%

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

et al. 2015

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“…A number of large eddy simulations (LESs) of laminar separation bubble flows over flat plates and airfoils have been completed in recent years. [28][29][30][31][32][33] Recent work demonstrated that accurate large eddy simulations of laminar separation bubble flows are possible using only O(1%) of the resolution required by a DNS. 34 However, filtering was necessary to damp artifacts at the computational boundary between the implicit and explicit grids.…”

Section: B Motivationmentioning

confidence: 99%

“…The constant Smagorinsky model has been compared to its dynamic counterpart and a no-model case. 28 Other investigators relied entirely on the dynamic Smagorinsky model, 29,31,32 or on the implicit numerical dissipation of their chosen scheme as in implicit LES or ILES, 33 and in one case even without any prior knowledge of the dissipative scheme's effects on the resolved scales. 30 Without benchmark DNS data and a baseline case with no subgrid-scale model active to compare directly to, the performance of their implicit and explicit models could not be evaluated quantitatively.…”

Section: B Motivationmentioning

confidence: 99%

Performance of subgrid-scale models in coarse large eddy simulations of a laminar separation bubble

Cadieux

Domaradzki

2015

Physics of Fluids

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The flow over many blades and airfoils at moderate angles of attack and Reynolds numbers ranging from 104 to 105 undergoes separation due to the adverse pressure gradient generated by surface curvature. In many cases, the separated shear layer then transitions to turbulence and reattaches, closing off a recirculation region—the laminar separation bubble. An equivalent problem is formulated by imposing suitable boundary conditions for flow over a flat plate to avoid numerical and mesh generation issues. Recent work demonstrated that accurate large eddy simulation (LES) of such a flow is possible using only O(1%) of the direct numerical simulation (DNS) resolution but the performance of different subgrid-scale models could not be properly assessed because of the effects of unquantified numerical dissipation. LES of a laminar separation bubble flow over a flat plate is performed using a pseudo-spectral Navier-Stokes solver at resolutions corresponding to 3% and 1% of the chosen DNS benchmark by Spalart and Strelets (2000). The negligible numerical dissipation of the pseudo-spectral code allows an unambiguous assessment of the performance of subgrid-scale models. Three explicit subgrid-scale models—dynamic Smagorinsky, σ, and truncated Navier-Stokes (TNS)—are compared to a no-model simulation (under-resolved DNS) and evaluated against benchmark DNS data focusing on two quantities of critical importance to airfoil and blade designers: time-averaged pressure (Cp) and skin friction (Cf) predictions used in lift and drag calculations. Results obtained with explicit subgrid-scale models confirm that accurate LES of laminar separation bubble flows is attainable with as low as 1% of DNS resolution, and the poor performance of the no-model simulation underscores the necessity of subgrid-scale modeling in coarse LES with low numerical dissipation.

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“…However, the magnitude of acoustic disturbances fed back into a boundary layer grows very rapidly as the inflow Mach number increases, which may cause reattachment via the development of an AFL, at the Reynolds number quite lower than 50, 000. In the numerical study conducted at Re = 2.3 × 10 4 and M = 0.2 [5], boundary-layer reattachment also occurs on an NACA0012…”

Section: Time-averaged Aerodynamic Forcesmentioning

confidence: 99%

Self-Noise Effects on Aerodynamics of Cambered Airfoils at Low Reynolds Number

Ikeda¹,

Atobe²,

Fujimoto³

et al. 2015

AIAA Journal

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Aerodynamics of cambered airfoils are investigated numerically, using NACA four-digit series of 6% thickness at low Reynolds number Re = 10, 000, and moderate Mach number M = 0.2, by focusing on the relation of aeroacoustic effects and hydrodynamic flow unsteadiness. Two-dimensional numerical simulations show that the onset of an acoustic feedback loop (AFL) leads to an abrupt increase in lift force. Associated with the feedback process, the evolution of two-dimensional vortices in the suction-side boundary layer shifts a separation bubble toward the leading edge, which causes a relatively steep pressure recovery near the trailing edge. Through a parametric study on airfoil shape, the aerodynamically favorable feature of aft camber is further enhanced with the presence of an AFL. In addition, the aft camber airfoil successfully forms a laminar separation bubble in three-dimensional calculations at the present Reynolds number, developing transitional behavior on the suction side, supposedly prompted by the airfoil tones. Although the boundary layer shows three-dimensional complexity, still the formation of an AFL is strongly suggested, via the comparison of spanwise correlations.

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Large-Eddy Simulation of Low-Reynolds-Number Flow Over Thick and Thin NACA Airfoils

Cited by 83 publications

References 17 publications

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

Mechanisms of surface pressure distribution within a laminar separation bubble at different Reynolds numbers

Performance of subgrid-scale models in coarse large eddy simulations of a laminar separation bubble

Self-Noise Effects on Aerodynamics of Cambered Airfoils at Low Reynolds Number

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