Large Eddy Simulation based on the Residual-based Variational Multiscale Method and Lagrangian Dynamic Smagorinsky Model

Tran, Steven A.; Sahni, Onkar

doi:10.2514/6.2016-0341

Cited by 6 publications

(4 citation statements)

References 26 publications

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“…Therefore, a combined subgrid-scale model was employed which uses the RBVMS model for the cross-stress terms and the dynamic Smagorinsky eddy-viscosity model for the Reynolds stress terms. This was done in both a finite element code [10,13] and a spectral code [12]. The combined subgrid-scale model is defined as…”

Section: A Combined Model Formulationmentioning

confidence: 99%

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Large Eddy Simulation of Surging Airfoils at High Advance Ratio and Reynolds Number

Rane

Sahni

2018

2018 Applied Aerodynamics Conference

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Large eddy simulation (LES) is performed for a surging NACA 0012 airfoil at high advance ratios and Reynolds numbers. The airfoil is subjected to sinusoidal oscillations in the streamwise direction at a fixed frequency and angle of attack in a constant free-stream flow. Three Reynolds numbers of Re=40,000, 200,000 and 1,000,000 are considered together with two advance ratios of λ=1.0 and 1.2, i.e., six cases are considered in total. We note that at the higher advance ratio the relative flow velocity becomes negative and a reversed flow condition is reached. Overall a similar trend is observed in the lift force among all cases. The peak normalized lift is about 9% lower for the highest Reynolds number case as compared to the lower Reynolds number cases for each advance ratio. On the other hand, the peak normalized lift is about 21% higher for the higher advance ratio case as compared to the lower advance ratio case for each Reynolds number, which is the difference in the peak dynamic pressure between the two advance ratios. Flow field also reveals a similar behavior among all cases with prominent features of flow separation near the (geometric) leading edge during the beginning of the retreating phase and formation of a dominant leading edge vortex (LEV). We observe that as the Reynolds number increases the LEV is formed later in the cycle (for a given advance ratio) while as the advance ratio increases it is formed earlier in the cycle (for a given Reynolds number). LEV evolution is also quantified based on its size and position. The central core of the LEV is found to fit the Rankine vortex model. As expected, a larger LEV is obtained for the lowest Reynolds number while LEV remains closest to the airfoil for the highest Reynolds number. At the higher advance ratio the LEV initially moves to the left past the geometric leading edge for each Reynolds number. This is expected since the relative flow velocity becomes negative (or a reversed flow condition is obtained). Further, the slope of the horizontal displacement in each case is remarkably close to the free-stream velocity, i.e., the LEV is advected in the horizontal direction at the free-stream velocity.

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Section: A Combined Model Formulationmentioning

confidence: 99%

“…where, as before, A H represents a local averaging operator. This is equivalent to averaging over local pathtubes [10,13] and maintains the utility of the local VGI.…”

Section: Local Vgi Computationmentioning

confidence: 99%

Large Eddy Simulation of Surging Airfoils at High Advance Ratio and Reynolds Number

Rane

Sahni

2018

2018 Applied Aerodynamics Conference

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“…, where τ C and τ M are stabilization parameters (e.g., see details in Tran and Sahni 9,10 ). This provides a closure to the coarse-scale problem as it involves coarsescale solution as the only unknown.…”

Section: Iia Combined Model Formulationmentioning

confidence: 99%

“…Current LES approach is based on the finite element (FE) method and uses a combined subgrid-scale model which employs the residual-based variational multiscale (RBVMS) model along with the dynamic Smagorinsky model. [8][9][10] The dynamic procedure is based on a localized version of the variational Germano identity (VGI). 8,9 An arbitrary Lagrangian Eulerian (ALE) description is used to account for the relative motion of the airfoil.…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of Surging Airfoils with Moderate to Large Streamwise Oscillations

Kocher

Cummings

Tran

et al. 2017

55th AIAA Aerospace Sciences Meeting

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A large eddy simulation (LES) based numerical investigation is carried out for flow over two surging airfoils with moderate to large streamwise oscillations. In each case, the airfoil is subjected to a sinusoidal surging motion with streamwise oscillation at a fixed angle of attack. The amplitude of the sinusoidal oscillation is varied within a moderate range as well as in the high range. The amplitude of oscillation is characterized by the advance ratio, which is defined as the ratio of the maximum relative velocity in excess to the mean relative velocity (or mean free-stream velocity) to the mean relative velocity. The relative velocity is defined between the airfoil and ambient fluid. For the moderate range, NACA 0018 airfoil at a mean Reynolds number of 300,000 and 4 • angle of attack is considered. Two advance ratios of 0.34 and 0.51 are considered to match with the experiments of Strangfeld et al. 1 For the high range, NACA 0012 airfoil at a mean Reynolds number of 40,000 and 6 • angle of attack is considered at three advance ratios of 0.8, 1.0 and 1.2 to match with the experiments of Granlund et al. 2 Note that the highest advance ratio case involves the reversed flow condition, where in a part of the surging cycle the relative flow becomes negative or is from the geometric trailing end of the airfoil to the leading end. Lift force is compared between the experiments and simulations. Overall a good agreement is obtained for the lift force in all cases. Additionally, for all cases flowfields from simulations are examined at different phases of the surge cycle. For the moderate advance ratio cases, a similar flow pattern is observed between the two advance ratios and no distinct vortex is shed from the airfoil. On the other hand, in all three high advance ratio cases a distinct vortex is shed near the (geometric) leading edge on the suction or upper side. This prominent leading-edge vortex is shed as the minimum velocity is reached in the surging cycle and advects downstream (in the horizontal direction) by roughly the mean free-stream velocity. The relative position of the shed vortex (with respect to the airfoil) varies significantly between the three high advance ratio cases; it crosses the leading edge before sweeping over the airfoil in the case with the highest advance ratio of 1.2 (i.e., in the case with the reverse flow regime).

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Large Eddy Simulation of Flow Interactions of a Finite-span Synthetic Jet on an Airfoil

Tran

McGlynn

Sahni

2017

55th AIAA Aerospace Sciences Meeting

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Large Eddy Simulation based on the Residual-based Variational Multiscale Method and Lagrangian Dynamic Smagorinsky Model

Cited by 6 publications

References 26 publications

Large Eddy Simulation of Surging Airfoils at High Advance Ratio and Reynolds Number

Large Eddy Simulation of Surging Airfoils at High Advance Ratio and Reynolds Number

Large Eddy Simulation of Surging Airfoils with Moderate to Large Streamwise Oscillations

Large Eddy Simulation of Flow Interactions of a Finite-span Synthetic Jet on an Airfoil

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