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Abstract
This dissertation presents a vortexparticle mesh method for bluff body aerodynamics using iterative Brinkman penalization, local mesh refinement and largeeddysimulation. The method relies on regularized Green’s function solutions to the unbounded Poisson equation. The Poisson solver is based on the convolution approach by Hockney and Eastwood (1988) and is extended to a mixture of unbounded, periodic and homogeneous Dirichlet or Neumann conditions. A mixture of unbounded and periodic conditions is achieved using the technique of Chatelain and Koumoutsakos (2010), where the Poisson equation is initially Fourier transformed in the periodic directions. For each discrete wavenumber a modified Helmholtz equation of reduced dimensionality is then solved. The rate of convergence corresponds to the order of the regularization function used, either Gaussian or an ideal lowpass filter, which is demonstrated for test problems. Homogeneous Dirichlet or Neumann conditions are achieved using the method of images. The Poisson solver is implemented in parallel and demonstrated to be highly scalable. It is used within a remeshed vortexmethod and the consistency of this combination is demonstrated for a semiperiodic problem of an unstable system of two parallel vortex pairs also considered by Chatelain and Koumoutsakos (2010).
The vortex method is extended to handle solid bodies using the iterative Brinkman penalization technique by Hejlesen et al. (2015a) for three dimensional flow. An accurate prediction of bluff body flow requires that the solid interface is well resolved, hence a multiresolution formulation of the method is applied based on refinement patches. The technique depends on a superposition of solutions to a scaledecomposed Poisson equation, which are obtained level wise in a mesh hierarchy. The multiresolution method is applied for the flow past a circular cylinder at low Reynolds number (Re = 300) in three dimension.The obtained results are found to be in excellent agreement with what is reported in the literature, in terms of force coefficients, growth rate and the topology of spectral profile of the primary unstable mode of the transition from two to three dimensional flow.
Largeeddysimulations using two different subgridscale stress models are implemented and verified for benchmark cases of homogeneous turbulence. Subsequently, the models are applied for bluff body flow at moderate Reynolds number (Re ≥ 10^{4}). A qualitative good agreement is obtained with experimental and numerical results from the literature, but several challenges of the method applied for such applications are also identified.
The vortex method is extended to handle solid bodies using the iterative Brinkman penalization technique by Hejlesen et al. (2015a) for three dimensional flow. An accurate prediction of bluff body flow requires that the solid interface is well resolved, hence a multiresolution formulation of the method is applied based on refinement patches. The technique depends on a superposition of solutions to a scaledecomposed Poisson equation, which are obtained level wise in a mesh hierarchy. The multiresolution method is applied for the flow past a circular cylinder at low Reynolds number (Re = 300) in three dimension.The obtained results are found to be in excellent agreement with what is reported in the literature, in terms of force coefficients, growth rate and the topology of spectral profile of the primary unstable mode of the transition from two to three dimensional flow.
Largeeddysimulations using two different subgridscale stress models are implemented and verified for benchmark cases of homogeneous turbulence. Subsequently, the models are applied for bluff body flow at moderate Reynolds number (Re ≥ 10^{4}). A qualitative good agreement is obtained with experimental and numerical results from the literature, but several challenges of the method applied for such applications are also identified.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Technical University of Denmark 
Number of pages  131 
ISBN (Electronic)  9788774755364 
Publication status  Published  2018 
Series  DCAMM Special Report 

Number  S248 
ISSN  09031685 
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Projects
 1 Finished

Two and Three Dimensional Modelling of Bridge Aerodynamics
Spietz, H. J., Walther, J. H., Hansen, M. O. L., Winckelmans, G. & Cottet, G.
01/04/2015 → 08/11/2018
Project: PhD