Advanced detached-eddy simulation of the MD 30P-30N three-element airfoil
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Cited by 2 publications
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On the Flow Past a Three-Element Wing: Mean Flow and Turbulent Statistics
Large eddy simulations (LES) on the flow past the 30P30N three-element high-lift wing at a moderate Reynolds number $$Re_c=750,000$$ R e c = 750 , 000 and three different angles of attack $$\alpha =5$$ α = 5 , 9 and $$23^\circ $$ 23 ∘ are conducted. The main focus is on the time-averaged statistics of the turbulent flow. The form drag noticeably increases with the angle of attack, while viscous drag remains roughly constant and contributes minimally to the total drag. This is associated with the significant pressure peaks found in the main element with increasing angles of attack and hence, the development of stronger adverse pressure gradients. At $$\alpha =23^\circ $$ α = 23 ∘ , this leads to the development of a prominent wake downstream this element that eventually evolves into a visible recirculation region above the flap, indicating the onset of stall conditions. In the flap, strong adverse pressure gradients are observed at small angles of attack instead, i.e., $$\alpha =5$$ α = 5 and $$9^\circ $$ 9 ∘ . This is attributed to the flap’s deflection angle with respect to the main wing, which causes a small separation of the boundary layer as the flow approaches the trailing edge. At the stall angle of attack, i.e., $$\alpha =23^\circ $$ α = 23 ∘ , the spread of the main element wake maintains attached the flow near the flap wall, thus mitigating the pressure gradient there and preventing the flow to undergo separation. The shear layers developed on the slat and main coves are also analysed, with the slat shear layer showing more prominence. In the slat, its size and intensity noticeably decrease with the angle of attack as the stagnation point moves towards the slat cusp. Conversely, the size of the shear layer developed in the main element cavity remains approximately constant regardless of the angle of attack. At the lower angles of attack, i.e., $$\alpha =5$$ α = 5 and $$9^\circ $$ 9 ∘ , the development of the shear layer is anticipated by the turbulent separation of the flow along the pressure side of the main wing, leading to increased levels of turbulence downstream. At the higher angle of attack, i.e., $$\alpha =23^\circ $$ α = 23 ∘ , the shear layer is originated by the cavity separation and transition to turbulence occurs within the cavity.
On the Flow Past a Three-Element Wing: Mean Flow and Turbulent Statistics
Large eddy simulations (LES) on the flow past the 30P30N three-element high-lift wing at a moderate Reynolds number $$Re_c=750,000$$ R e c = 750 , 000 and three different angles of attack $$\alpha =5$$ α = 5 , 9 and $$23^\circ $$ 23 ∘ are conducted. The main focus is on the time-averaged statistics of the turbulent flow. The form drag noticeably increases with the angle of attack, while viscous drag remains roughly constant and contributes minimally to the total drag. This is associated with the significant pressure peaks found in the main element with increasing angles of attack and hence, the development of stronger adverse pressure gradients. At $$\alpha =23^\circ $$ α = 23 ∘ , this leads to the development of a prominent wake downstream this element that eventually evolves into a visible recirculation region above the flap, indicating the onset of stall conditions. In the flap, strong adverse pressure gradients are observed at small angles of attack instead, i.e., $$\alpha =5$$ α = 5 and $$9^\circ $$ 9 ∘ . This is attributed to the flap’s deflection angle with respect to the main wing, which causes a small separation of the boundary layer as the flow approaches the trailing edge. At the stall angle of attack, i.e., $$\alpha =23^\circ $$ α = 23 ∘ , the spread of the main element wake maintains attached the flow near the flap wall, thus mitigating the pressure gradient there and preventing the flow to undergo separation. The shear layers developed on the slat and main coves are also analysed, with the slat shear layer showing more prominence. In the slat, its size and intensity noticeably decrease with the angle of attack as the stagnation point moves towards the slat cusp. Conversely, the size of the shear layer developed in the main element cavity remains approximately constant regardless of the angle of attack. At the lower angles of attack, i.e., $$\alpha =5$$ α = 5 and $$9^\circ $$ 9 ∘ , the development of the shear layer is anticipated by the turbulent separation of the flow along the pressure side of the main wing, leading to increased levels of turbulence downstream. At the higher angle of attack, i.e., $$\alpha =23^\circ $$ α = 23 ∘ , the shear layer is originated by the cavity separation and transition to turbulence occurs within the cavity.
On the dynamics of the turbulent flow past a three-element wing
A comprehensive analysis of the unsteady flow dynamics past the 30P30N three-element high lift wing is performed by means of large eddy simulations at different angles of attack (α = 5°, 9°, and 23°) and at a Reynolds number of Rec=750 000 (based on the nested chord). Results are compared with experimental and numerical investigations, showing a quantitatively good agreement and, thus, proving the reliability and accuracy of the present simulations. Within the slat and main coves, large recirculation bubbles are bounded by shear layers, where the onset of turbulence is triggered by Kelvin–Helmholtz instabilities. In the energy spectrum of the velocity fluctuations, the footprint of these instabilities is detected as a broadband peak; its frequency being moved toward lower values as the angle of attack increases. Kelvin–Helmholtz vortices roll-up and break down into small scales that eventually impinge into the slat and main coves lower surfaces. The slat impingement shows to be more prominent, and hence, larger velocity and pressure fluctuations are observed. The impingement strength diminishes with the angle of attack in both coves, while higher fluctuations are originated on the slat and main respective suction sides, leading to larger boundary layers. This is associated with the displacement of the stagnation point with the angle of attack. Another salient feature observed is the laminar-to-turbulent flow transition in the main and flap leading edges although the average location of this transition seems to not be affected by the angle of attack. Tollmien–Schlichting instabilities precede this transition, with the disturbances amplified by the inviscid mode at low angles of attack, while at α=23°, the local Reynolds number on the main suction side is incremented and the viscous mode becomes important. The analysis shows that the turbulent wake formed at the trailing edge of all elements dominates the dynamics downstream. This is especially true at the higher angle of attack, where a large region of velocity deficit above the flap is observed, thus indicating the onset of stall conditions.
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