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This page is a copy of research/scientific_computing/former/cad (Wed, 31 Aug 2022 15:00:52)

Computational methods for unsteady Aerodynamics

High order finite difference methods have been developed. We use so called summation-by-parts operators, penalty techniques for implementing boundary and interface conditions, and the energy method for proving stability. We have developed summation-by-parts difference operators for first and second derivatives as well as artificial dissipation operators. The scientific results discussed above have materialized in a three-dimensional, stable high-order, finite-difference multi-block code for the Navier-Stokes equations.

Another line of work deals with the analysis and improvement of finite volume "production codes". In that analysis, we have reused the framework mentioned above for the high order finite difference methods and been able to analyze the most commonly used methodology (by domestic and international industry and national labs) for aerodynamic calculations. Also in the finite volume case, we derived summation-by-parts operators for first and second derivatives as well as suitable artificial dissipation operators.

The above mentioned analysis of the finite difference and finite volume methods prompted the development of a new type of stable hybrid methods, where we combine the advantages of both methods in an efficient and stable way. This development will enable the coupling of finite difference and finite volume methods into a very efficient hybrid code for time-dependent aerodynamics and aeroacoustics.

Another major interest is in boundary conditions for the Euler and Navier-Stokes equations. We have analyzed existing frequently used techniques as well as derived completely new formulations. The boundary conditions have been analyzed to see whether they lead to well-posed and stable approximations.

Future aeronautical applications based on the Navier-Stokes or Euler equations will include more and more multi-physics problem. Typical examples include fluid-structure interaction, flows in accelerating frames, flow induced heat transfer, flows with chemical reactions, etc. The significant computational requirements of coupled systems makes the coupling strategy very important. We are interested in well posedness for multiple equations sets as well as stable numerical coupling procedures.

We will also take into account various kinds of uncertainties related to aerodynamic problems. Typical examples include uncertainties in the geometry of a wing, the speed of the aircraft and the angle of attack. Ultimately, we aim for a computational methodology that delivers an answer with error bars.

The development above have been done in a collaboration with NASA Langley Research Center, Center for Turbulence Research (CTR) at Stanford University, University of the Witwatersrand (WITS) and the Council for Scientific and Industrial Research (CSIR) in South Africa, Nanospace AB, and the Swedish Defence Research Agency (FOI).

Head of group Jan Nordström

Projects

Shock calculations using high order accurate solvers

Computing solutions containing discontinuities such as shock waves, require numerical schemes designed specifically for that purpose. Currently we apply a very high order Euler/Navier Stokes finite difference solver to shock diffraction problems. The code is built on numerical techniques developed during the last decade by Uppsala University and NASA Langley. For an increased accuracy in shock regions, we are looking at the possibilities of implementing shock capturing techniques like the WENO or MUSCL schemes into our linearly stable solver. Further we will consider an extended set of geometries like multi facetted convex walls and cylindrical surfaces, which experimentally have been shown to have numerous interesting flow features. This work is a joint collaboration between Uppsala University, Stanford University (Center for Turbulence Research) and the University of Witwatersrand.

Contact and further information: Qaisar Abbas

Hybrid methods for unsteady aerodynamics

Fluid Structure Interaction (FSI) problems is a typical example of an aeronautical multi-physics problem. It deals with the physics that occur as air interacts with the structure of an aircraft. One of our objectives is to investigate whether the generally accepted formulations of the FSI-problems are the only possible ones. We also aim for a stable numerical coupling. Initial attempts are made on a one-dimensional problem using the linearized Euler equations as the flow model and a spring as a model of the solid part. Later the combination of finite volume methods on unstructured grids and high order finite difference methods on structured grids can be considered to meet the demands of accuracy and the possibility of handling complex geometries. The project is a collaboration with the Council for Scientific and Industrial Research (CSIR) in South Africa and the Center of Turbulence Research (CTR) at Stanford University, USA.

Contact and further information: Sofia Eriksson

Computational methods for heat transfer in micro-mechanical systems

Micro Electro Mechanical Systems (MEMS) refer to devices that have characteristic size scale between one micro- and one millimeter which combine electronic and mechanical components. Over the past 50 years they have provided a vast area of research due to the technological improvements in micro- and nanoscale manufacturing techniques. The goal of this project is to develop numerical methods for simulating heat transfer in a complex geometry microchannel. The results will be used in space applications to improve the efficiency of a gas propulsion system by heating the gas flow which will results in control of the flow rate and higher specific impulse. This is a joint project with Nanospace AB.

Contact and further information: Jens Berg

Numerical analysis of uncertainties in aerodynamics

Modeling atmospheric dispersion of poisonous agents in urban environment requires accurate numerical methods that can handle a wide range of scenarios. In addition to the existence of potentially very different agents, the physical problem is also assumed to include several kinds of stochastic behavior, such as uncertainty in geometry, initial state and wind direction. A dispersion model for the problem must therefore include various kinds of uncertainty, as well as fulfilling demands on resolution of different scales of time and concentrations. This project is a collaboration between Stanford University (Center for Turbulence Research) and Uppsala University.

Contact and further information: Per Pettersson

Refereed Publications

  • Extrapolation procedures for the time-dependent Navier-Stokes equations. Jan Nordström. In AIAA Journal, volume 30, pp 1654-1656, 1992.

Theses

Technical Reports

Updated  2022-08-31 15:00:52 by Victor Kuismin.