Tesis doctoral de Oriol Lehmkuhl Barba
This thesis aims at developing a numerical methodology suitable for the direct numerical simulation (dns) and large-eddy simulation (les) of turbulent flows in order to be used in complex flows, currently encountered in industrial application. at the same time, the study of such turbulent flows can be an opportunity for gaining insight into the complex physics associated with them. to accomplish these goals, the mathematical formulation, conservative spatial discretization on unstructured grids and time- integration scheme for solving the navier-stokes equations are presented. The spatial discretization proposed preserves the symmetry properties of the continuous differential operator and ensure both, stability and conservation of the global kinetic energy balance on any grid. Furthermore, the time-integration technique proposed is an efficient self-adaptive strategy, based on a one-parameter second-order-explicit scheme, which has been successfully tested on both cartesian staggered and unstructured collocated codes, leading to cpu cost reductions of up to 2.9 and 4.3, respectively. after presenting the general methodology for computing flows in complex geometries with unstructured grids, different les models and regularization models suitable for these kind of meshes are presented and assessed by means of the analysis of different flows. First, regularization models are tested by means of the simulation of different cases with different level of complexity of the mesh. From a structured grid to a very complex mesh, with zones composed of prism and tetrahedral control volumes. It has been shown, that regularization models are very dependent on the quality of the filtering process. Although good results can be obtained with structured or smooth unstructuredmeshes, their performance is affected under fully irregular unstructured grids. A possible remedy to circumvent this issue is also presented. The main idea is to formulate the c4 model within a les template. Although preliminary results are promising, further testing is still required. after regularization model assessment, les models are also tested in a natural convection flow. It is shown that, although first order statistics are well solved for most of the models tested (with the exception of the smagorinsky model), qr- and dynamic-smagorinsky models present a better prediction of the second-order statistics. However, if cpu time is considered, then qr model is the best alternative. the second part of the thesis is devoted to the study of turbulent flows past bluff bodies. The cases studied are: the flow past a sphere, the flow past a circular cylinder and the flow past a naca 0012 airfoil. All these cases shares some characteristics encountered in turbulent flows with massive separations, i.E., Flow separation, transition to turbulence in the separated shear-layers and turbulent wakes with periodic shedding of vortices. However there are intrinsic characteristics of the turbulence in each of them, which make them interesting for the studying of the turbulence. Furthermore, the results presented for the flow past a sphere at re = 3700 and 10000, together with the flow past a naca 0012 at re=50000 and aoa = 8 are the first dns results presented in the literature for both flows. conclusions drawn from the good results obtained point out that the use of the conservative formulation presented in this thesis, is one of the keys for the success of the sgs models used. This formulation, together with the use of unstructured grids might be a step towards the use of les models for solving industrial flows on complex geometries at high reynolds numbers.
Datos académicos de la tesis doctoral «Numerical resolution of turbulent flows on complex geometries.«
- Título de la tesis: Numerical resolution of turbulent flows on complex geometries.
- Autor: Oriol Lehmkuhl Barba
- Universidad: Politécnica de catalunya
- Fecha de lectura de la tesis: 26/07/2012
Dirección y tribunal
- Director de la tesis
- Assensi Oliva Llena
- Tribunal
- Presidente del tribunal: Antonio Lecuona neumann
- pedro Jorge Martins coelho (vocal)
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- (vocal)