| 1. |
- Görtz, Stefan, et al.
(författare)
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Evaluation of the Recursive Projection Method for Efficient Unsteady Turbulent CFD Simulations
- 2004
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Ingår i: 24th INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES. ; , s. 1-13
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Konferensbidrag (refereegranskat)abstract
- The Recursive Projection Method (RPM) hasbeen implemented into an unstructured CFD code to improve the efficiency of dual time steppingfor unsteady turbulent CFD simulations.RPM is a combined implicit-explicit method that enhances convergence. It can easily be implementedinto existing codes and the solver’s existing acceleration techniques can be used withoutchange. The method has been evaluated by computing the periodic self-induced shock oscillations over an 18% thick biconvex airfoil at0◦ angle of attack, a Mach number of 0.76 anda Reynolds number of 11 million. On average,RPM accelerated the convergence of the innerloop of dual time stepping to a predefined convergencecriterion by a factor of about 2.5.
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| 2. |
- Görtz, Stefan, et al.
(författare)
-
Recursive Projection Method for efficient unsteady CFD simulations
- 2004
-
Konferensbidrag (refereegranskat)abstract
- The Recursive Projection Method (RPM) has been implemented into the unstructured grid CFD code EDGE to accelerate the inner-loop convergence of dual time stepping. The method tries to identify the slowly converging subspace and applies Newton iterations in this subspace together with a fixed point scheme in the complement. The method has been employed to compute the steady and unsteady viscous flow around a circular cylinder for a Reynolds number of 100. When converging to machine accuracy, RPM accelerated the convergence of the steady-state solution by a factor of 2.5. The time-accurate simulations were accelerated by a factor of about two.
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| 3. |
- Görtz, Stefan
(författare)
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Unsteady euler and detached-eddy simulations of vortex breakdown over a full-span delta wing
- 2004
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Ingår i: ECCOMAS 2004 - European Congress on Computational Methods in Applied Sciences and Engineering. ; , s. 1-20
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Konferensbidrag (refereegranskat)abstract
- The inherently unsteady flow field over a stationary, full-span delta wing at high incidence is simulated time-accurately using the structured Navier-Stokes Multi Block (NSMB) code. Inviscid calculations are performed on an Euler-type grid using explicit global Runge-Kutta time stepping. Detached-Eddy Simulations (DES) are done on a Navier-Stokes grid using implicit dual time stepping. The full-span model Euler simulations capture vortex interactions - the numerical solutions exhibit asymmetry as well as streamwise fluctuations in the port and starboard vortex breakdown locations, despite symmetric boundary conditions and a symmetric computational grid. Flow visualization reveals that spiral-type breakdown is predicted over both sides of the wing for the predominant part of the simulations. The rotation of the port and starboard post-breakdown helical structures is shown to be out of phase at certain times. Intermittent bubble-type breakdown is also observed to occur periodically over one side or the other of the wing and related to the occurrence of asymmetry in the vortex breakdown location. For DES, a time step study and a grid sensitivity study are conducted on semi-span grids to verify time accuracy and grid resolution. The full-span DES results are compared to detailed LDV and pressure measurements for the same geometry. The breakdown location is shown to be grid sensitive. Agreement between the measured and computed breakdown locations is shown to be good on the refined grid. The surface pressure distribution is underestimated, even on the refined grid, maybe due to excessive wind-tunnel blockage effects.
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| 4. |
- Görtz, Stefan, et al.
(författare)
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Virtual-reality environment for visualization of unsteady three-dimensional CFD data
- 2004
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Ingår i: ECCOMAS 2004 - European Congress on Computational Methods in Applied Sciences and Engineering. ; , s. 1-20
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Konferensbidrag (refereegranskat)abstract
- A Virtual-Reality (VR) environment has been set up to visualize, explore and interact with steady and time-dependent three-dimensional CFD solutions in a fully immersive way. The paper presents the VR system and provides some examples of currently investigated applications in the area of computational aerodynamics, such as the unsteady flow over a full-span delta wing at high angle of attack, the steady hypersonic flow around an atmospheric reentry vehicle and the steady airflow around a human female standing in a strong headwind. These pre-computed three-dimensional flows have been visualized interactively in a six-sided CAVE, demonstrating that the sheer sensual impact of the immersive display has a powerful effect on the physical intuition. Several user can move around freely in the VR environment, without being distracted from the flow to be investigated by the analytical tools and menus. The users have a common experience and can discuss the visualized flow field while interacting with it. Our experience with using VR for visualizing, exploring and analyzing complex unsteady three-dimensional CFD data are summarized and benefits and limitations are highlighted.
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