| 1. |
- Tomac, Maximilian, et al.
(författare)
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Factors in fluencing accurate shock vortex interaction prediction on F-16XL aircraft
- 2014
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Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014. - Reston, Virginia : American Institute of Aeronautics and Astronautics Inc.. - 9781624102561
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Konferensbidrag (refereegranskat)abstract
- Computational Fluid Dynamics methods continues to play an increasingly important role in design and validation. Some examples are conditions that can not be tested prior to flight test. In order to rely on these methods it is essential that these methods are validated and evaluated to state-of-the-art wind tunnel test and/or in-flight data. In a previous project \Cranked-Arrow Wing Aerodynamics Project International" (CAWAPI)it was clear that all CFD methods failed to some degree in the transonic regime where shock vortex interaction phenomena was present. Detailed analysis of surface pressure distribution showed that CFD where not able replicate the correct flow field and produce acceptable results.This paper aim to map out the flight conditions for which CFD is likely to fail, and try to answer or shed light in the question why? This with the main focus on the factors that influence shock vortex interaction in the flow field.
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| 2. |
- Goetzendorf-Grabowski, Tomas, et al.
(författare)
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Coupling Adaptive-Fidelity CFD with S&C Analysis to Predict Flying Qualities
- 2009
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Ingår i: 27th AIAA Applied Aerodynamics Conference.
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Konferensbidrag (refereegranskat)abstract
- CEASIOM, the Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods, is a framework tool that integrates discipline-specific tools for conceptual design. At this early stage of the design it is very useful to be able to predict the °ying and handling qualities of this design. In order to do this, the aerodynamic database needs to be computed for the configuration being studied which then has to be coupled to the stability and control tools to carry out the analysis. This paper describes how the adaptive-fidelity CFD module of CEASIOM computes the aerodynamic dataset of an air craft configuration, and how that dataset is analyzed by the SDSA module to determine the °ying qualities of the aircraft. These predicted °ying qualities are then compared with the °ight-test data of the Ranger 2000 trainer aircraft in order to verify the goodness of the overall approach.
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| 3. |
- Mendenhall, M.R., et al.
(författare)
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Comparing and benchmarking engineering methods for the prediction of X-31 aerodynamics
- 2012
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 20:1, s. 12-20
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Tidskriftsartikel (refereegranskat)abstract
- A number of useful engineering methods are available for fast and economic estimates of the aerodynamic characteristics of complex flight vehicles. This article investigates the application of three specific engineering methods to the X-31 fighter configuration, and CFD, wind tunnel, and flight test data are used for comparison and evaluation purposes. The emphasis is on static longitudinal stability aspects up to high angles of attack; however, selected asymmetric and unsteady effects are considered. Results from the engineering methods are in good agreement with experiment and CFD for angles of attack up to 15° for most cases and higher angles for some cases. Results for pitching moment are in good agreement with CFD, but many of the nonlinear characteristics of the airplane are not predicted by the engineering methods. The quality of the longitudinal stability results is discussed in terms of the prediction of the center of pressure on the vehicle. The results provide improved understanding of the continued usefulness of engineering methods as an analysis tool during the design phase and into the flight test diagnostic phase of a new aircraft.
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| 4. |
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| 5. |
- Tomac, Maximilian, et al.
(författare)
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Low speed high alpha prediction on F-16XL aircraft
- 2014
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Ingår i: 52nd AIAA Aerospace Sciences Meeting - AIAA Science and Technology Forum and Exposition, SciTech 2014. - : American Institute of Aeronautics and Astronautics.
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Konferensbidrag (refereegranskat)abstract
- This article presents the comparisons of the results of the CFD study around the F- 16XL CAWAPI configuration. The progress since the original CAWAPI has been made on the solver side by implementing several numerical techniques improving convergence of the numerical process as well as lowering numerical viscosity needed to stabilize the calculations. In addition, innovative hybrid RANS-LES model (HYB0) has been tested and a new much denser grid has been generated.
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| 6. |
- Tomac, Maximilian, et al.
(författare)
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Predictions of stability and control for a flying wing
- 2014
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Ingår i: Aerospace Science and Technology. - : Elsevier BV. - 1270-9638 .- 1626-3219. ; 39, s. 179-186
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Tidskriftsartikel (refereegranskat)abstract
- The numerical simulation of a generic reduced radar signature tailless aircraft is considered. Investigation compares simulated data to low-speed wind tunnel experiments. Focus is on numerical predictions of steady longitudinal and lateral aerodynamics and influence of control surfaces on aerodynamic forces. Fully turbulent and transitional Reynolds Averaged Navier-Stokes (RANS) simulations predicted in agreement with experiment unstable pitch characteristics for low angles of attack (alpha), this was not the case for inviscid or laminar simulations. However, all simulations captured a sudden rapid increase in nose up pitch moment at higher angles of attack compared to experiments. Time accurate computations (URANS) captured non-linearity and unsteadiness in yaw moment with respect to differential split flap deflections for the studied angles of attack.
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| 7. |
- Tomac, Maximilian, et al.
(författare)
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Steps Towards Automated Robust RANS Meshing
- 2013
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Ingår i: Proceedings of the 4:th CEAS Conference in Linkoping, 2013. - : Linköping University Electronic Press. - 9789175195193 ; , s. 114-123
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The creation of high-quality discretizations for use in viscous flow simulations remains a challenging task. Even with modern software tools and substantial human effort, the application of state-of-the-art mesh generation algorithms in the presence of geometric features such as concave corners may still result in inadequate local mesh configurations, which can severely affect the resolution of important flow features. To address such issues, mesh generation tools for hybrid unstructured grids often expose a considerable number of algorithm configuration parameter. The resulting flexibility does indeed enable the creation of sufficiently resolved hybrid meshes, although the process often requires a very considerable amount of time even for an experienced user. In a production environment where a large number of detailed simulations of single aircraft configuration are performed, the cost in terms of man-hours may be acceptable. For other applications with requirements for short turn-around time, a more automated approach is desirable. Since an automatic mesh generation procedure cannot rely on user intervention for the resolution of geometric complications or edge cases, a robust strategy for the handling of the surface geometry en- countered in realistic aircraft configurations must be implemented.The approach presented here is based on a segregated prismatic/tetrahedral mesh generation procedure, and aims to achieve robustness by means of local geometric modifications. Criteria chosen and algorithmic modifications make use of similar principles as in earlier work, but are adapted for the specific requirements of mesh generation for aircraft configura- tions. An existing set of open-source tools is exploited for mesh data structures, file format support, surface mesh generation and tetrahedral volume meshes.The mesh generation strategy presented is based on four phases, starting with the creation of a sufficiently resolved surface mesh. In a second step, the envelope mesh of the prismatic boundary layer mesh is determined; the robustness of this stage is the primary contribution of the present work. Thirdly, tetrahedral elements are generated to fill the volume between the envelope of the prismatic layer and the farfield boundaries, and finally, pentahedral elements are grown between adapted wall and envelope mesh.The algorithm implemented into existing open source libraries was applied to two applications presented in this study, a fairly simple wing-body-stabilizer configuration typical for a tran- sonic transport aircraft (CRM) and a rather complex, detailed geometry of a delta wing fighter prototype (F-16XL). RANS solutions converged to engineering accuracy are found to yield solutions in close agreement with meshes produced by a well established grid generator for the EDGE flow solver provided that comparable resolutions are used for both the prismatic layer and the tetrahedral domain.When comparing mesh generation timings, an interesting observation was made. For the common situation where parallel CFD solutions are performed on a compute cluster, the analyst may be evaluating post-processed results of a simulation based on a mesh created with the method presented in this paper before a serial advancing front mesh generation has even been completed.Obviously, this does not mean that there is no need for high-quality advancing-front mesh generation tools. A substantial proportion of relevant geometries and flight conditions likely require more detailed control over mesh generation parameters than is available in a hybrid Delaunay method. However, for routine solutions where serial mesh generation time is a bottleneck, the libraries including the present method can be used to accelerate the turnaround time considerably.
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| 8. |
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