Israeli Computational Fluid Dynamics Center

Caesarea, Israel

Israeli Computational Fluid Dynamics Center

Caesarea, Israel

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Adar M.,Israeli Air Force | Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center | Levy Y.,Israeli Computational Fluid Dynamics Center
50th Israel Annual Conference on Aerospace Sciences 2010 | Year: 2011

Detached Eddy Simulation models are studied to asses their applicability to the complex cavity flows. Three hybrid models, all based on a k-ω turbulence model, are considered and applied to a flat plat flow, an unsteady separated flow about a hump, and a 2D cavity flow. The results show that DES models are necessary for a reliable simulation of unsteady separated flows. Furthermore, the delayed detached eddy simulation (DDES) and a newly proposed hybrid model, the X-DDES provide the means to relieve the grid dependency in the hybrid model filter.


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.


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.


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.


Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center | Silverman I.,Israeli Computational Fluid Dynamics Center | Kidron Y.,Israeli Computational Fluid Dynamics Center | Levy Y.,Israeli Computational Fluid Dynamics Center
50th Israel Annual Conference on Aerospace Sciences 2010 | Year: 2011

In this work, a density-based, fully-compressible, Reynolds-Averaged Navier-Stokes flow solver for multi-phase flows is developed. The solver is based on the extension of the HLLC scheme to compute the convective flux for multi-phase flows. The flow field is assumed to be in a kinematic and thermodynamic equilibrium and is modeled via a homogeneous mixture formulation. The Reynolds-stress tensor is modeled by a two-equation k-ω turbulence model, including the required correction due to significant compressibility effects. Liquid-gaseous phase exchange is modeled via a cavitation model.


Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center | Levy Y.,Israeli Computational Fluid Dynamics Center | Carmel E.,Israeli Computational Fluid Dynamics Center
50th Israel Annual Conference on Aerospace Sciences 2010 | Year: 2011

A robust implicit time integration scheme of the Spalart-Allmaras (SA) turbulence model in a curvilinear coordinate system is proposed. The mean-flow equations and the SA model equation are integrated in a loosely coupled manner. Thanks to the loosely coupled strategy, the unconditionally positive-convergent implicit time integration scheme, originally developed for two-equation turbulence models, is utilized. The mean-flow equations and the SA model equation are discretized using finite-differences. The convective flux vector is approximated using the upwind HLLC scheme with the passive scalar approach for the SA model. Since an upwind scheme is used, a free-stream subtraction is applied and its treatment within the unconditionally positive-convergent scheme is addressed. Numerical experiments are conducted, simulating the flow field about the RAE2822 airfoil, the ONERA M6 wing and about the DLR-F6 wing-body configuration. Results from the numerical simulations show that the scheme exhibits good convergence characteristics, and it always preserve the positivity of the SA model dependent variable.


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.


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.


Karpel M.,Technion - Israel Institute of Technology | Shousterman A.,Israeli Computational Fluid Dynamics Center | Maderuelo C.,Airbus | Climent H.,Airbus
AIAA Journal | Year: 2015

Linear structural dynamics, unsteady aerodynamics, control system, and actuator models are combined for linear aeroservoelastic equations of motion that are augmented with nonlinear feedback loops based on the increased-order modeling approach. Although the linear equations are formulated in the frequency domain for best combined efficiency, accuracy, and robustness in industrial environment, the nonlinear feedback loops are modeled in the time domain to provide maximal flexibility in adding nonlinear effects in all the involved disciplines. The linear equations are solved first to provide a baseline response to deterministic or stochastic gusts, maneuver commands, or directforce excitations using fast Fourier transform techniques. Nonlinear effects are then added in a time-marching process that modifies the linear solution using convolution integrals. The numerical process was used in the Dynresp code that was recently developed as a framework for industrial applications and research in the area of nonlinear structural dynamics. The procedure is outlined with emphasis on structural nonlinearities using a fictitious-mass technique. The numerical example exhibits limit-cycle oscillations due to actuator nonlinearities. © 2015 by H. Hafsteinsson. Published by the American Institute of Aeronautics and Astronautics, Inc.


Kidron Y.,Israeli Computational Fluid Dynamics Center | Mor-Yossef Y.,Israeli Computational Fluid Dynamics Center | Levy Y.,Israeli Computational Fluid Dynamics Center
AIAA Journal | Year: 2010

A novel, Cartesian-grid-based flow solver is developed for predicting complex high-Reynolds-number turbulent flowfields. The Cartesian grid generator is based on the cut-cell approach using cell merge and Cartesian layer techniques. Cartesian layers imitate the structured grid approach in which the mesh is stretched gradually. Local refinement is added based on local surface curvature. As a turbulence closure model, the two equation κ-ω-TNT turbulence model is successfully implemented using an unconditionally positive-convergent implicit time integration scheme. The overall flow solver's robustness and accuracy are verified using three challenging test cases. The numerical results convincingly demonstrate the robustness and accuracy of the flow solver, especially in predicting aerodynamic forces.

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