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Visar resultat 6 - 10 av 46 avhandlingar som matchar ovanstående sökkriterier.

1. 6. Transport Barriers in Plasmas and Fluids

   Författare :Robert Moestam; Chalmers tekniska högskola; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; DNS; transport barriers; Zonal flows; L-H mode transition; turbulence simulations; drift waves; flux tube simulations; nonlinear instabilities; linear instabilities;

   Sammanfattning : In the present work different mechanisms for generation and suppression of turbulence are studied. The suppression of nonlinearly generated turbulence stabilized by temperature boundary conditions as well as turbulence generated by linear instabilities and suppressed by nonlinearly generated secondary flows are treated. LÄS MER

3. 7. Numerical study of flame dynamics

   Författare :Arkady Petchenko; Vitaly Bychkov; Leonid Kagan; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; combustion; Direct Numerical Simulation DNS ; turbulence; flame-vortex interaction; flame acceleration; flame-acoustic interaction; Physics; Fysik;

   Sammanfattning : Modern industrial society is based on combustion with ever increasing standards on the efficiency of burning. One of the main combustion characteristics is the burning rate, which is influenced by intrinsic flame instabilities, external turbulence and flame interaction with walls of combustor and sound waves. LÄS MER

4. 8. Transition delay in boundary-layer flows via reactive control

   Författare :Nicolò Fabbiane; Dan S. Henningson; Shervin Bagheri; Denis Sipp; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; flow control; drag reduction; net energy saving; adaptive control; model-based control; optimal control; flat-plate boundary layer; laminar-to- turbulent transition; plasma actuator; direct numerical simulation; in-flight experiments; strömningsstyrning; friktionsreduktion; netto energibesparing; adaptiv styrning; modellbaserad styrning; optimal kontroll; gränsskikt öve en plan platta; laminärt till turbulent omslag; plasma aktuator; DNS; flyg prov; Engineering Mechanics; Teknisk mekanik;

   Sammanfattning : Transition delay in boundary-layer flows is achieved via reactive control of flow instabilities, i.e. Tollmien-Schlichting (TS) waves. Adaptive and model-based control techniques are investigated by means of direct numerical simulations (DNS) and experiments. LÄS MER

5. 9. Numerical studies of transtion in wall-bounded flows

   Författare :Ori Levin; Dan Henningson; Nikolaus Adams; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layer; suction; wall jet; streaks; waves; periodic disturbance; localized disturbance; turbulent spot; algebraic growth; exponential growth; stability; transition thresholds; transition prediction; PSE; DNS; Fluid mechanics; Strömningsmekanik;

   Sammanfattning : Disturbances introduced in wall-bounded flows can grow and lead to transition from laminar to turbulent flow. In order to reduce losses or enhance mixing in energy systems, a fundamental understanding of the flow stability and transition mechanism is important. LÄS MER

7. 10. 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