Sökning: "wall turbulence"

Visar resultat 16 - 20 av 179 avhandlingar innehållade orden wall turbulence.

1. 16. Spectral-element simulations of turbulent wall-bounded flows including transition and separation

   Författare :Johan Malm; Dan Henningson; Philipp Schlatter; Suad Jakirlic; KTH; []
   Nyckelord :spectral-element method; direct numerical simulation DNS ; large-eddy simulation LES ; turbulence; transition; over-integration; three-dimensional separation; massively parallel simulations; proper orthogonal decomposition POD ; Koopman modes; vorticity stretching; coherence; SRA - E-vetenskap SeRC ; SRA - E-Science SeRC ;

   Sammanfattning : The spectral-element method (SEM) is used to study wall-bounded turbulent flowsin moderately complex geometries. The first part of the thesis is devoted to simulations of canonical flow cases, such as temporal K-type transitionand turbulent channel flow, to investigate general resolution requirements and computational efficiency of the numerical code nek5000. LÄS MER

3. 17. Stability analysis and transition prediction of wall-bounded flows

   Författare :Ori Levin; KTH; []
   Nyckelord :Boundary layer; wall jet; algebraic growth; exponential growth; lift-up effect; streamwise streaks; Tollmien-Schlichting waves; free-stream turbulence; roughness element; transition prediction; Parabolized Stability Equations; Direct Numerical S;

   Sammanfattning : Disturbances introduced in wall-bounded .ows can grow andlead to transition from laminar to turbulent .ow. In order toreduce losses or enhance mixing in energy systems, afundamental understanding of the . LÄS MER

4. 18. Numerical and modelling aspects of large-eddy and hybrid simulations of turbulent flows

   Författare :Matteo Montecchia; Arne V. Johansson; Gert Brethouwer; Stefan Wallin; Dominic Von Terzi; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; turbulence; wall-bounded flows; large-eddy simulation; SGS modelling; OpenFOAM; hybrid RANS-LES; Engineering Mechanics; Teknisk mekanik;

   Sammanfattning : In this study, the explicit algebraic sub-grid scale (SGS) model (EAM) has been extensively validated in wall-resolved large-eddy simulations (LES) of wall-bounded turbulent flows at different Reynolds numbers and a wide range of resolutions. Compared to eddy-viscosity based models, the formulation of the EAM is more consistent with the physics and allows to accurately capture SGS anisotropy,which is relevant especially close to walls. LÄS MER

5. 19. Mechanistic Modeling of Wall-Fluid Thermal Interactions for Innovative Nuclear Systems

   Författare :Roman Thiele; Henryk Anglart; Xu Cheng; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; GEN-IV reactors; Wall heat transfer; Computational Fluid Dynamics; Wall functions; Reactor design; Supercritical water; Liquid metal; Energy Technology; Energiteknik; Fysik; Physics;

   Sammanfattning : Next generation nuclear power plants (GEN-IV) will be capable of not only producing energy in a reliable, safe and sustainable way, but they will also be capable of reducing the amount of nuclear waste, which has been accumulated over the lifetime of current-generation nuclear power plants, through transmutation. Due to the use of new and different coolants, existing computational tools need to be tested, further developed and improved in order to thermal-hydraulically design these power plants. LÄS MER

7. 20. Modelling of subgrid-scale stress and passive scalar flux in large eddy simulations of wall bounded turbulent flows

   Författare :Linus Marstorp; Arne V. Johansson; Pierre Comte; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Turbulence; large-eddy simulation; subgrid-scale model; Fluid mechanics; Strömningsmekanik;

   Sammanfattning : The aim of the thesis is to develop and validate subgrid-scale models that are relevant for large eddy simulations of complex flows including scalar mixing. A stochastic Smagorinsky model with adjustable variance and time scale is developed by adding a stochastic component to the Smagorinsky constant. LÄS MER