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Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center
51st Israel Annual Conference on Aerospace Sciences 2011 | Year: 2011

Progress toward a stable and efficient numerical treatment for the compressible Favre-Reynolds-averaged Navier-Stokes equations with a Reynolds-stress turbulence model (RSM) is presented. The numerical approach that is chosen relies on the use of a decoupled implicit time integration method, that is, the five mean-flow equations are solved separately from the Reynolds-stress, seven closure equations The key idea is the use of the unconditionally positive-convergent implicit scheme (UPC), originally developed for two-equation turbulence models. The use of the UPC scheme in the RSM implementation guarantees the positivity of the normal Reynolds-stress components and the turbulent (specific) dissipation rate. Thanks to the UPC matrix-free structure and the decoupled approach, the computational effort is significantly reduced. Numerical experiments are conducted, simulating two- and three-dimensional complex flows. Results obtained from the numerical simulations demonstrate the overall flow solver robustness. Source


Selitrennik E.,Technion - Israel Institute of Technology | Karpel M.,Technion - Israel Institute of Technology | Levy Y.,Israeli Computational Fluid Dynamics Center
Journal of Aircraft | Year: 2012

A new approach for computational fluid dynamics-based aeroelastic simulation of rapidly morphing flight vehicles is presented. The morphing vehicle consists of a number of components interconnected by actuators and contact constraints. Due to aerodynamic, inertial, and actuation loads, the overall structure undergoes largedisplacement morphing. The method assumes that each component experiences large rigid-body displacements and small elastic deformations that are linear combinations of the individual normal modes. The structural equations of motion are based on the fictitious-mass substructure modal synthesis method, which is expanded to allow large rotations between the structural components while keeping displacements and rotation compatibility at the interface coordinates. The compatibility equations are time-dependent, and the inclusion of their time derivatives in the equations of motion introduces nonlinear dynamic effects. The resulting generalized-coordinate nonlinear matrix equations of motion are embedded in a time-accurate computational fluid dynamics code. The vector of generalized forces includes aerodynamic forces from the computational fluid dynamics solution as well as inertial and actuation forces. The computational process is demonstrated by two different wing-body configurations where the wings are rotating from parallel to perpendicular positions relative to the body. The morphing simulations demonstrate a robust and stable computational process that exhibits significant aeroelastic effects. Source


Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center
53rd Israel Annual Conference on Aerospace Sciences 2013 | Year: 2013

Numerical treatment for the compressible Favre-Reynolds-averaged Navier-Stokes equations with a Reynolds-stress model (RSM) on unstructured grids is presented. The mean-flow and the Reynolds stress model equations are discretized using a finite volume method that is based on second order accuracy. The time-marching approach that is chosen relies on the use of a decoupled implicit time integration method, that is, the five mean-flow equations are solved separately from the Reynolds-stress, seven closure equations. The key idea is the use of the unconditionally positive-convergent implicit scheme (UPC), originally developed for two-equation turbulence models. The use of the UPC scheme in the RSM implementation guarantees the positivity of the normal Reynolds-stress components and the turbulence (specific) dissipation rate for any time step. Thanks to the UPC matrix-free structure and the decoupled approach, the computational scheme is very efficient. Results obtained from the numerical simulations show that the scheme preserves the positivity of the normal Reynolds stress components, and the dissipation of turbulence, for an infinite time step. The flow solver robustness is also reflected by the ability to initiate the simulations from a uniform solution based on the free-stream values. Source


Friedman C.,Technion - Israel Institute of Technology | Friedman C.,George Washington University | Arieli R.,Technion - Israel Institute of Technology | Levy Y.,Israeli Computational Fluid Dynamics Center
Journal of Aircraft | Year: 2016

Circulation control airfoils modify the lift by changing the jet momentum (injected tangenttoa blunt trailing edge), whereas conventional sharp trailing-edge airfoils control their lift primarily by changing the angle of attack. For a step input in the angle of attack, the lift develops with a certain indicial time lag, which for sharp trailing-edge airfoils may be represented by Wagner's function. This paper explores the similarities between Wagner's lift build-up function and lift build-up over elliptical circulation control airfoils using numerical simulations for a 15% thicknessto-chord ratio elliptic circulation control airfoil. Following a thorough validation, the lift response to a step change in jet momentum is simulated using time-accurate flow simulations. The results highlight an excellent correlation between the time lagsof the Wagner function and the circulation control airfoil lift response to the corresponding step input, suggesting that the Wagner function may lend itself for representing circulation control lift dynamics. Additional transient behaviors are also compared, and similarities as well as ranges of applicability are discussed. Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Source


Fastovsky D.,P.O.B. | Lapidot D.,P.O.B. | Gat Y.,P.O.B. | Levy Y.,Israeli Computational Fluid Dynamics Center
52nd Israel Annual Conference on Aerospace Sciences 2012 | Year: 2012

In the present work, numerical flow simulations of a complex aerodynamic configuration of a missile were conducted. The configuration consists of 3 consecutive different aerodynamic surfaces: classical tapered wing, X-Tail stabilizers with flaps control surfaces and an additional annular wing tail. The annular wing tail configuration is an efficient solution to adapt the missile for a helicopter launch version with an aft rocket booster that maintains the required roll controllability. This research employed the EZNSS (Elastic Zonal Navier-Stokes Solver) CFD code *. Good agreement of the CFD results with wind tunnel tests was found for the tested cases. The results confirm that this CFD solver was found to successfully handle complex aerodynamic configurations. Source

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