On the Vortex Breakdown Phenomenon in High Angle of Attack Flows Over Delta Wing Geometries

2014 ◽  
Author(s):  
Eric D. Robertson ◽  
Varun Chitta ◽  
D. Keith Walters ◽  
Shanti Bhushan
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Wing Model

Using computational methods, an investigation was performed on the physical mechanisms leading to vortex breakdown in high angle of attack flows over delta wing geometries. For this purpose, the Second International Vortex Flow Experiment (VFE-2) 65° sweep delta wing model was studied at a root chord Reynolds number (Recr) of 6 × 106 at various angles of attack. The open-source computational fluid dynamics (CFD) solver OpenFOAM was used in parallel with the commercial CFD solver ANSYS® FLUENT. For breadth, a variety of classic closure models were applied, including unsteady Reynolds-averaged Navier-Stokes (URANS) and detached eddy simulation (DES). Results for all cases are analyzed and flow features are identified and discussed. The results show the inception of a pair of leading edge vortices originating at the apex for all models used, and a region of steady vortical structures downstream in the URANS results. However, DES results show regions of massively separated helical flow which manifests after vortex breakdown. Analysis of turbulence quantities in the breakdown region gives further insight into the mechanisms leading to such phenomena.

Detached-Eddy Simulations and Reynolds-Averaged Navier-Stokes Simulations of Delta Wing Vortical Flowfields

2002 ◽  
Vol 124 (4) ◽  
pp. 924-932 ◽  
Author(s):  
Scott Morton ◽  
James Forsythe ◽  
Anthony Mitchell ◽  
David Hajek
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Fighter Aircraft ◽  
Eddy Simulation ◽  
Reynolds Averaged Navier Stokes ◽  
High Reynolds

An understanding of vortical structures and vortex breakdown is essential for the development of highly maneuverable vehicles and high angle of attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missiles at extreme flight conditions. Demands for more maneuverable air vehicles have pushed the limits of current CFD methods in the high Reynolds number regime. Simulation methods must be able to accurately describe the unsteady, vortical flowfields associated with fighter aircraft at Reynolds numbers more representative of full-scale vehicles. It is the goal of this paper to demonstrate the ability of detached-eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS)/large-eddy Simulation (LES) method, to accurately predict vortex breakdown at Reynolds numbers above 1×106. Detailed experiments performed at Onera are used to compare simulations utilizing both RANS and DES turbulence models.

Delayed Detached-Eddy Simulation and Application of a Coflow Jet Airfoil at High Angle of Attack

2013 ◽  
Vol 444-445 ◽  
pp. 270-276
Author(s):  
Wen Biao Gan ◽  
Zhou Zhou ◽  
Xiao Ping Xu ◽  
Rui Wang
Keyword(s):  
Angle Of Attack ◽  
Aircraft Design ◽  
Simulation Method ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Flow Vortex ◽  
Cylinder Flow

A DDES (Delayed Detached-Eddy Simulation) method is presented and applied to simulation and design of a CFJ (Coflow Jet) airfoil at high angle of attack. The method is based on average vorticity, and is used to predict a number of test cases, including a circular cylinder flow, vortex design and simulation of the CFJ airfoil. The results demonstrate that the DDES method is efficient for CFJ airfoil flow. It provides reference to flow control and aircraft design.

Numerical Investigation on the Coanda Effect Over the S809 Airfoil With Synthetic Jet Actuator at High Angle of Attack

2014 ◽  
Author(s):  
Mohammad Moshfeghi ◽  
Nahmkeon Hur
Keyword(s):  
Angle Of Attack ◽  
Synthetic Jet ◽  
Coanda Effect ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
High Angle Of Attack ◽  
Injection Angle ◽  
Eddy Simulation ◽  
Momentum Coefficient ◽  
Coandǎ Effect

Synthetic jet actuators (SJA) have shown their efficiency in manipulating the aerodynamic forces on airfoils and blades. Generally, the injection angle is assumed to be an important factor for the injection-based flow control techniques, especially in moderate separation. However, it is important to know the level of effectiveness and the aerodynamic mechanism through which a SJA may affect an airfoil at a high angle of attack. The present research studies the effects of angle between the injected flow and the surface’s tangent line (Coanda effect) over the S809 airfoil equipped with a SJA, using detached eddy simulation (DES). The airfoil is assumed to be at an angle of attack of 25°. Three different cases with jet flow angles of 5°, 15° and 25° are simulated at a constant momentum coefficient of 4.5×10−3. The SJA frequency is 125 Hz for all cases and the simulations are conducted at the Reynolds number of one million. The effects of the jet angle on the streamline, pressure distribution and lifts and drag values are investigated.

Detached Eddy Simulation of Complex Separation Flows Over a Modern Fighter Model at High Angle of Attack

2017 ◽  
Vol 22 (5) ◽  
pp. 1309-1332 ◽  
Author(s):  
Yang Zhang ◽  
Laiping Zhang ◽  
Xin He ◽  
Xiaogang Deng ◽  
Haisheng Sun
Keyword(s):  
Flow Field ◽  
Angle Of Attack ◽  
Vortical Flow ◽  
Leeward Side ◽  
Detached Eddy Simulation ◽  
High Angle ◽  
Flow Topology ◽  
High Angle Of Attack ◽  
Eddy Simulation ◽  
Separation Flows

AbstractThis paper presents the simulation of complex separation flows over a modern fighter model at high angle of attack by using an unstructured/hybrid grid based Detached Eddy Simulation (DES) solver with an adaptive dissipation second-order hybrid scheme. Simulation results, including the complex vortex structures, as well as vortex breakdown phenomenon and the overall aerodynamic performance, are analyzed and compared with experimental data and unsteady Reynolds-Averaged Navier-Stokes (URANS) results, which indicates that with the DES solver, clearer vortical flow structures are captured and more accurate aerodynamic coefficients are obtained. The unsteady properties of DES flow field are investigated in detail by correlation coefficient analysis, power spectral density (PSD) analysis and proper orthogonal decomposition (POD) analysis, which indicates that the spiral motion of the primary vortex on the leeward side of the aircraft model is highly nonlinear and dominates the flow field. Through the comparisons of flow topology and pressure distributions with URANS results, the reason why higher and more accurate lift can be obtained by DES is discussed. Overall, these results show the potential capability of present DES solver in industrial applications.

scholarly journals Leading Edge Blowing to Mimic and Enhance the Serration Effects for Aerofoil

2021 ◽  
Vol 11 (6) ◽  
pp. 2593
Author(s):  
Yasir Al-Okbi ◽  
Tze Pei Chong ◽  
Oksana Stalnov
Keyword(s):  
Boundary Layer ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Boundary Layer Separation ◽  
Shear Instability ◽  
Vortical Flow ◽  
High Angle ◽  
High Angle Of Attack ◽  
Layer Separation ◽  
Aerodynamic Performances

Leading edge serration is now a well-established and effective passive control device for the reduction of turbulence–leading edge interaction noise, and for the suppression of boundary layer separation at high angle of attack. It is envisaged that leading edge blowing could produce the same mechanisms as those produced by a serrated leading edge to enhance the aeroacoustics and aerodynamic performances of aerofoil. Aeroacoustically, injection of mass airflow from the leading edge (against the incoming turbulent flow) can be an effective mechanism to decrease the turbulence intensity, and/or alter the stagnation point. According to classical theory on the aerofoil leading edge noise, there is a potential for the leading edge blowing to reduce the level of turbulence–leading edge interaction noise radiation. Aerodynamically, after the mixing between the injected air and the incoming flow, a shear instability is likely to be triggered owing to the different flow directions. The resulting vortical flow will then propagate along the main flow direction across the aerofoil surface. These vortical flows generated indirectly owing to the leading edge blowing could also be effective to mitigate boundary layer separation at high angle of attack. The objectives of this paper are to validate these hypotheses, and combine the serration and blowing together on the leading edge to harvest further improvement on the aeroacoustics and aerodynamic performances. Results presented in this paper strongly indicate that leading edge blowing, which is an active flow control method, can indeed mimic and even enhance the bio-inspired leading edge serration effectively.

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