| 1. |
- Efraimsson, Gunilla, et al.
(författare)
-
A note on the effect of artificial viscosity on solutions of conservation laws
- 1996
-
Ingår i: Applied Numerical Mathematics. - : Elsevier. - 0168-9274 .- 1873-5460. ; 21, s. 155-173
-
Tidskriftsartikel (refereegranskat)abstract
- We consider central difference schemes with artificial viscosity terms for nonlinear hyperbolic systems. We analyze the influence of artificial viscosity on solutions with shocks of nonlinear hyperbolic problems in one dimension. Both stationary and moving shocks are considered. The analysis shows that for the Euler equations one can obtain well behaved (sharp) shock layers when a scalar viscosity coefficient is used. This is not true for a general system. Numerical computations of Burgers' equation and the Euler equations are presented. They support the results from the linear theory.
|
|
| 2. |
- Efraimsson, Gunilla, et al.
(författare)
-
Analysis of Stretched Grids as Buffer Zones in Aero-Acoustic Simulations
- 2009
-
Ingår i: 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference). - Reston, Virigina : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A zone of increasingly stretched grid is a robust and easy-to-use way to avoid unwanted reections at artificial boundaries in aero-acoustic simulations. There are two main damping mechanisms, dissipation and under-resolution a traveling wave, respectively. In this paper the behavior of acoustic waves and wave packages, respectively, are studied via analysis of solutions to a semi-discrete linear boundary value problem. The solutions of the linear problem is compared to solutions of the full non-linear Euler equations.
|
|
| 3. |
|
|
| 4. |
- Kreiss, Gunilla, et al.
(författare)
-
Analysis of stretched grids as buffer zones in simulations of wave propagation
- 2016
-
Ingår i: Applied Numerical Mathematics. - : Elsevier BV. - 0168-9274 .- 1873-5460. ; 107, s. 1-17
-
Tidskriftsartikel (refereegranskat)abstract
- A zone of increasingly stretched grid is a robust and easy-to-use way to avoid unwanted reflections at artificial boundaries in wave propagating simulations. In such a buffer zone there are two main damping mechanisms, dissipation and under-resolution that turns a traveling wave into an evanescent wave. We present analysis in one and two space dimensions showing that evanescent decay through under-resolution is a very efficient way to damp waves. The analysis is supported by numerical computations.
|
|
| 5. |
- Kreiss, Gunilla, et al.
(författare)
-
Approximate solutions to slightly viscous conservation laws
- 2004
-
Ingår i: Quarterly of Applied Mathematics. - : American Mathematical Society (AMS). - 0033-569X .- 1552-4485. ; 62:1, s. 117-133
-
Tidskriftsartikel (refereegranskat)abstract
- We study an approximate solution of a slightly viscous conservation law in one dimension, constructed by two asymptotic expansions that are cut off after the third order terms. In the shock layer, an inner solution is valid and an outer solution is valid elsewhere. Based on the stability results in [10], we show that for a given time interval the difference between the approximate solution and the true solution is not larger than o(epsilon), where epsilon is the viscosity coefficient. The result holds for shocks of any strength.
|
|
| 6. |
- Kreiss, Gunilla, et al.
(författare)
-
Elimination of first order errors in shock calculations
- 2001
-
Ingår i: SIAM Journal on Numerical Analysis. - : SIAM PUBLICATIONS. - 0036-1429 .- 1095-7170. ; 38:6, s. 1986-1998
-
Tidskriftsartikel (refereegranskat)abstract
- First order errors downstream of shocks have been detected in computations with higher order shock capturing schemes in one and two dimensions. Based on a matched asymptotic expansion analysis we show how to modify the artificial viscosity and raise the order of accuracy.
|
|
| 7. |
- Bodén, Hans, et al.
(författare)
-
Aeroacoustics research in Europe : The CEAS-ASC report on 2012 highlights
- 2013
-
Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 332:25, s. 6617-6636
-
Forskningsöversikt (refereegranskat)abstract
- The Council of European Aerospace Societies (CEAS) Aeroacoustics Specialists Committee (ASC) supports and promotes the interests of the scientific and industrial aeroacoustics community on an European scale and European aeronautics activities internationally. In this context, "aeroacoustics" encompasses all aerospace acoustics and related areas. Each year the committee highlights some of the research and development projects in Europe. This paper is a report on highlights of aeroacoustics research in Europe in 2012, compiled from information provided to the ASC of the CEAS. During 2012, a number of research programmes involving aeroacoustics were funded by the European Commission. Some of the highlights from these programmes are summarized in this paper, as well as highlights from other programmes funded by national programmes or by industry. Enquiries concerning all contributions should be addressed to the authors who are given at the end of each subsection.
|
|
| 8. |
- Carbonne, Louis, et al.
(författare)
-
Use of Full Coupling of Aerodynamics and Vehicle Dynamics for Numerical Simulation of the Crosswind Stability of Ground Vehicles
- 2016
-
Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International.. - 1946-391X .- 1946-3928. ; 9:2, s. 359-370
-
Tidskriftsartikel (refereegranskat)abstract
- The prediction in the design phase of the stability of ground vehicles subject to transient crosswinds become of increased concern with drag reduced shapes, lighter vehicles as well as platooning. The objective of this work is to assess the order of model complexity needed in numerical simulations to capture the behavior of a ground vehicle passing through a transient crosswind. The performance of a full-dynamic coupling between aerodynamic and vehicle dynamic simulations, including a driver model, is evaluated. In the simulations a feedback from the vehicle dynamics into the aerodynamic simulation is performed in every time step. In the work, both the vehicle dynamic response and the aerodynamic forces and moments are studied. The results are compared to a static coupling approach on a set of different vehicle geometries. Five car-type geometries and one simplified bus geometry are evaluated. The aerodynamic loads and moments are obtained using Detached Eddy Simulation (DES) where the motion of the vehicle is enabled using an overset mesh technique. This motion is calculated with a single-track model, including a driver model and handling two degrees of freedom, namely lateral translation and yaw motion.The results show that for vehicles undertaking large yaw moments and therefore large yaw motions, like the bus-type geometry, the full dynamic coupling is beneficial. In this case, a static coupling overestimates the aerodynamic loads and in turn the vehicle motion. On less crosswind sensitive vehicles, like the car-type geometries, the full-coupling approach does not modify the results in a significant way compared to a static coupling.
|
|
| 9. |
- da Rocha-Schmidt, L., et al.
(författare)
-
Progress Towards Adaptive Aircraft Engine Nacelles
- 2014
-
Ingår i: 29th Congress of the International Council of the Aeronautical Sciences, ICAS. - : International Council of the Aeronautical Sciences.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Emissions and noise of aircraft engineshave to be significantly further reduced andefficiency further increased in the future. Onemeans is the improvement of airflow though theengine and especially so in its inlet region byproper shapes. Due to changes in the flightconditions, the optimal nacelle shape varies. Itwould thus be beneficial to be able to change thenacelle shape. Evaluations on system and enginelevels including related flow simulations supportthe identification of proper shaping parameters.Initial concepts of possible morphingtechnologies are discussed as well.
|
|
| 10. |
- Dahan, Jeremy A., et al.
(författare)
-
Numerical investigation of a realistic nose landing gear
- 2014
-
Ingår i: 20th AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A hybrid approach is used to study the noise generated by a realistic full-scale nose land- ing gear configuration. Compressible Detached-Eddy Simulations are performed to com- pute the flow field and the far-field noise is evaluated with the Ffowcs Williams-Hawkings acoustic analogy. Preliminary Reynolds-Averaged Navier-Stokes simulations are performed to evaluate the sensitivity of the steady solution to the computational grid. It is found that mesh independence is not obtained with the grids considered, although the agreement between the medium and fine grids is reasonable. The time-dependent solution obtained via DES is examined and the main noise sources on the gear surfaces are identified. The power spectral density of pressure uctuations on the tyre surface is found to be rather broadband on the noisier sides of the tyre, while distinct humps and a sharp peak near 1kHz are identified in the quieter regions of the tyre. This sharp peak is observed again in the far-field noise. Further work is needed to clarify the cause of this peak. Its frequency is too high to link it with shedding from a gear component, although it could be associated with unsteadiness near the tyre corner.
|
|
