Sökning: "flat-plate boundary layer"

Visar resultat 11 - 15 av 38 avhandlingar innehållade orden flat-plate boundary layer.

1. 11. Analysis and control of transitional shear flows using global modes

   Författare :Shervin Bagheri; Dan Henningson; Alessandro Bottaro; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Fluid mechanics; flow control; hydrodynamic stability; global modes; jet in crossflow; flat-plate boundary layer; laminar-turbulent transition; Arnoldi method; Koopman modes; balanced truncation; direct numerical simulations.; Fluid mechanics; Strömningsmekanik;

   Sammanfattning : In this thesis direct numerical simulations are used to investigate two phenomenain shear flows: laminar-turbulent transition over a flat plate and periodicvortex shedding induced by a jet in cross flow. The emphasis is on understanding and controlling the flow dynamics using tools from dynamical systems and control theory. LÄS MER

3. 12. Feedback control and modal structures in transitional shear flows

   Författare :Onofrio Semeraro; Dan S. Henningson; Mihailo Jovanoic; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; flow control; flat-plate boundary layer; laminar-turbulent transition; Other engineering mechanics; Övrig teknisk mekanik;

   Sammanfattning :   Two types of shear flows are investigated in this thesis; numerical simulations are performed for the analysis and control of the perturbation arising in a boundary layer over a flat plate, whereas PIV measurements are analysed for the investigation of a confined turbulent jet. Modal structures of the flows are identified: the aim is to understand the flow phenomena and to identify reduced-order models for the feedback control design. LÄS MER

4. 13. Active Control and Modal Structures in Transitional Shear Flows

   Författare :Onofrio Semeraro; Dan Henningson; Bernd Noack; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Flow control; flat-plate boundary layer; optimal controllers; model reduction; turbulent jet; POD; DMD; Koopman modes;

   Sammanfattning : Flow control of transitional shear flows is investigated by means of numerical simulations. The attenuation of three-dimensional wavepackets of Tollmien-Schlichting (TS) and streaks in the boundary layer is obtained using active control in combination with localised sensors and actuators distributed near the rigid wall. LÄS MER

5. 14. Study of generation, growth and breakdown of streamwise streaks in a Blasius boundary layer

   Författare :Luca Brandt; KTH; []
   Nyckelord :Fluid mechanics; laminar-turbulent transition; boundary layer flow; transient growth; streamwise streaks; lift-up effect; receptivity; free-stream turbulence; streak instability; secondary instability; Direct Numerical Simulation.;

   Sammanfattning : Transition from laminar to turbulent flow has beentraditionally studied in terms of exponentially growingeigensolutions to the linearized disturbance equations.However, experimental findings show that transition may occuralso for parameters combinations such that these eigensolutionsare damped. LÄS MER

7. 15. Simulations of turbulent boundary layers with suction and pressure gradients

   Författare :Alexandra Bobke; Philipp Schlatter; Ramis Örlü; Ayse Gul Gungor; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layers; near-wall turbulence; history effects; asymptotic suction boundary layers; large-eddy simulation;

   Sammanfattning : The focus of the present licentiate thesis is on the effect of suction and pressure gradients on turbulent boundary-layer flows, which are investigated separately through performing numerical simulations.The first part aims at assessing history and development effects on adverse pressure-gradient (APG) turbulent boundary layers (TBL). LÄS MER