| 1. |
- Eliasson, Peter, et al.
(författare)
-
IMPROVING STALL CHARACTERISTICS OF UCAV WING WITH VORTEX GENERATORS
- 2022
-
Ingår i: 33rd Congress of the International Council of the Aeronautical Sciences, ICAS 2022. - : International Council of the Aeronautical Sciences. ; , s. 2990-2998
-
Konferensbidrag (refereegranskat)abstract
- Recent Unmanned Combat Air Vehicle (UCAV) configurations have not-so-slender wings with moderate leading-edge sweepangles of 45◦ to 60◦. Planforms vary from pure delta to diamond and even lambda more or less blended wing bodies with a relatively small thickness ratio at the inner wing/fuselage region. The performance and low-observable signature considerations require a compromise between a small radar cross-section and lifting surface shapes for long range and sufficient agility. The airflow is governed largely by the progression of vortices shed from the wing leading edge which interact and produce non-linear aerodynamics. Like early swept wing fighters like the Saab 32 the UCAV may exhibit undesirable flying characteristics over part of the envelope with tip stall and pitch-up. Such problems were mitigated by vortex control "devices" like leading edge fences and notches which violate the low observable requirement. The AVT-181 SACCON is a well studied case. We attempt to improve its stalling characteristics by mimicking the leading edge fence action by a configuration of very small vortex generators and study their effect by CFD.
|
|
| 2. |
|
|
| 3. |
- Eliasson, Peter, et al.
(författare)
-
Influence of Transition on High-Lift Prediction with the NASA Trap Wing Model
- 2011
-
Konferensbidrag (refereegranskat)abstract
- A computational analysis on the influence of the transition for the NASA Trap Wing Model has been carried out, which is an extension of the work presented for the 1st AIAA High Lift Prediction Workshop. The transition prediction is based on stability analyses with a database method in spanwise sections. Comparisons with experimental data are made to find appropriate N-factors for the eN method leading to the estimated interval 5< N <10. The computed transition locations are used to specify laminar and turbulent regions in the 3D calculations. Including transition improves the results, especially with locations from higher N-factors, and good agreement with experimental data for aerodynamic forces, moments and pressure distributions is obtained.
|
|
| 4. |
- Mialon, Bruno, et al.
(författare)
-
Validation of numerical prediction of dynamic derivatives : The DLR-F12 and the Transcruiser test cases
- 2011
-
Ingår i: Progress in Aerospace Sciences. - : Elsevier BV. - 0376-0421 .- 1873-1724. ; 47:8, s. 674-694
-
Forskningsöversikt (refereegranskat)abstract
- The dynamic derivatives are widely used in linear aerodynamic models in order to determine the flying qualities of an aircraft: the ability to predict them reliably, quickly and sufficiently early in the design process is vital in order to avoid late and costly component redesigns. This paper describes experimental and computational research dealing with the determination of dynamic derivatives carried out within the FP6 European project SimSAC. Numerical and experimental results are compared for two aircraft configurations: a generic civil transport aircraft, wing-fuselage-tail configuration called the DLR-F12 and a generic Transonic CRuiser, which is a canard configuration. Static and dynamic wind tunnel tests have been carried out for both configurations and are briefly described within this paper. The data generated for both the DLR-F12 and TCR configurations include force and pressure coefficients obtained during small amplitude pitch, roll and yaw oscillations while the data for the TCR configuration also include large amplitude oscillations, in order to investigate the dynamic effects on nonlinear aerodynamic characteristics. In addition, dynamic derivatives have been determined for both configurations with a large panel of tools, from linear aerodynamic (Vortex Lattice Methods) to CFD. This work confirms that an increase in fidelity level enables the dynamic derivatives to be calculated more accurately. Linear aerodynamics tools are shown to give satisfactory results but are very sensitive to the geometry/mesh input data. Although all the quasi-steady CFD approaches give comparable results (robustness) for steady dynamic derivatives, they do not allow the prediction of unsteady components for the dynamic derivatives (angular derivatives with respect to time): this can be done with either a fully unsteady approach i.e. with a time-marching scheme or with frequency domain solvers, both of which provide comparable results for the DLR-F12 test case. As far as the canard configuration is concerned, strong limitations for the linear aerodynamic tools are observed. A key aspect of this work are the acceleration techniques developed for CFD methods, which allow the computational time to be dramatically reduced while providing comparable results.
|
|
| 5. |
- Moens, Frédéric, et al.
(författare)
-
Transition Prediction and Impact on 3D High-Lift Wing Configuration
- 2007
-
Ingår i: A collection of technical papers. - : American Institute of Aeronautics and Astronautics. - 9781563478987 ; , s. 1593-1613
-
Konferensbidrag (refereegranskat)abstract
- The evolution of maximum lift coefficient of a transport aircraft as a function of Reynolds number can be linked to modifications of the laminar-turbulent transition process. In the framework of European project EUROLIFT (I), a task was dedicated to the physical understanding and the numerical modeling of the transition process in high-lift configurations. Then, in the follow-on project EUROLIFT II, a major step is the integration of transition prediction tools within Reynolds-averaged Navier-Stokes (RANS) solvers in order to estimate the impact of transition on performance. This paper presents an overview of the different activities dealing with transition in the EUROLIFT II project.
|
|
| 6. |
- Moens, Frédéric, et al.
(författare)
-
Transition Prediction and Impact on a Three-Dimensional High-Lift-Wing Configuration
- 2008
-
Ingår i: Journal of Aircraft. - : American Institute of Aeronautics and Astronautics (AIAA). - 0021-8669 .- 1533-3868. ; 45:5, s. 1751-1766
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of the maximum-lift coefficient of a transport aircraft as a function of Reynolds number can be linked to modifications. of the laminar-turbulent transition process. In the framework of European project EUROLIFT I, a task was dedicated to the physical understanding and the numerical modeling of the transition process in high-lift configurations. Then in the follow-up project EUROLIFT II, a major step was the integration of transition-prediction tools within Reynolds-averaged Navier-Stokes solvers to estimate the impact of transition on performance. This paper presents an overview of the different activities dealing with transition in the EUROLIFT II project.
|
|
| 7. |
- Otero, Evelyn, et al.
(författare)
-
Acceleration on stretched meshes with line-implicit LU-SGS in parallel implementation
- 2015
-
Ingår i: International journal of computational fluid dynamics (Print). - : Informa UK Limited. - 1061-8562 .- 1029-0257. ; 29:2, s. 133-149
-
Tidskriftsartikel (refereegranskat)abstract
- The implicit lower-upper symmetric Gauss-Seidel (LU-SGS) solver is combined with the line-implicit technique to improve convergence on the very anisotropic grids necessary for resolving the boundary layers. The computational fluid dynamics code used is Edge, a Navier-Stokes flow solver for unstructured grids based on a dual grid and edge-based formulation. Multigrid acceleration is applied with the intention to accelerate the convergence to steady state. LU-SGS works in parallel and gives better linear scaling with respect to the number of processors, than the explicit scheme. The ordering techniques investigated have shown that node numbering does influence the convergence and that the orderings from Delaunay and advancing front generation were among the best tested. 2D Reynolds-averaged Navier-Stokes computations have clearly shown the strong efficiency of our novel approach line-implicit LU-SGS which is four times faster than implicit LU-SGS and line-implicit Runge-Kutta. Implicit LU-SGS for Euler and line-implicit LU-SGS for Reynolds-averaged Navier-Stokes are at least twice faster than explicit and line-implicit Runge-Kutta, respectively, for 2D and 3D cases. For 3D Reynolds-averaged Navier-Stokes, multigrid did not accelerate the convergence and therefore may not be needed.
|
|
| 8. |
- Otero, Evelyn, et al.
(författare)
-
Convergence Acceleration of the CFD Code Edge by LU-SGS
- 2011
-
Ingår i: 3rd CEAS European Air & Space Conference, Venice, 24-28 October 2011. - : CEAS/AIDAA. ; , s. 606-611
-
Konferensbidrag (refereegranskat)abstract
- Edge is a flow solver for unstructured grids based on a dual grid and edge-based formulation. The standard dual-time stepping methods for compressible unsteady flows are inadequate for large-scale industrial problems. This has motivated the present work, in which an implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) type of relaxation has been implemented in the code Edge with multigrid acceleration. Two different types of dissipation, a scalar and a matrix model, have been constructed which increase the diagonal dominance of the system matrix but not the numerical viscosity of the computed solution. A parametric study demonstrates convergence accelerations by a factor of three for inviscid transonic flows compared to explicit Runge-Kutta smoothing for multigrid acceleration.
|
|
| 9. |
- Otero, Evelyn, et al.
(författare)
-
Implementation of Implicit LU-SGS method with Line-implicit scheme on Stretched Unstructured Grids
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A first implementation of line-implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) in Edge has been considered in this paper for convergenceacceleration on stretched meshes. The motivation comes from the lack of efficiency of the implicit LU-SGS when running in RANS meshes. Edge is a flow solver for unstructured grids based on a dual grid and edge-based formulation. The line-implicit method has been implemented in the code Edge has an acceleration method when computing explicit schemes in stretched meshes. This methods works only in regions of stretched grid where the flow equations are integrated implicitly in time along the structured lines. The combination with an implicit LU-SGS should remove the restriction of the time step for explicit schemes and accelerate the convergence to steady state. The results have shown that for highly stretched meshes, line-implicit LU-SGS could perform much faster than LU-SGS.
|
|
| 10. |
- Otero, Evelyn, et al.
(författare)
-
Parameter Investigation with Line-Implicit Lower-Upper Symmetric Gauss-Seidel on 3D Stretched Grids
- 2014
-
Konferensbidrag (refereegranskat)abstract
- An implicit Lower-Upper Symmetric Gauss-Seidel (LU-SGS) solver has been implemented as a multigrid smoother combined with a line-implicit methodas an acceleration technique for Reynolds-Averaged Navier-Stokes (RANS) simulation on stretched meshes.The Computational Fluid Dynamics code concerned is Edge, an edge-based finite volume Navier-Stokesflow solver for structured and unstructured grids.The paper focuses on the investigation of the parameters related to our novel line-implicit LU-SGSsolver for convergence acceleration on 3D RANS meshes. The LU-SGS parameters are defined as the Courant-Friedrichs-Lewy number, the Left Hand Side dissipation,and the convergence of iterative solution of the linear problem arising from the linearisation of the implicit scheme.The influence of these parameters on the overall convergence is presented and default values are defined formaximum convergence acceleration. The optimized settings are applied to 3D RANScomputations for comparison with explicit and line-implicit Runge-Kutta smoothing. For most of the cases, a computing time acceleration of the order of 2 is found depending on the mesh type, namely the boundary layer and the magnitude of residual reduction.
|
|
