Sökning: "laminar-to- turbulent transition"

Visar resultat 1 - 5 av 21 avhandlingar innehållade orden laminar-to- turbulent transition.

1. 1. 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

3. 2. Transition in Particle-laden Flows

   Författare :Joy Klinkenberg; Luca Brandt; Shuisheng He; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Transition; modal analysis; non-modal analysis; multi-phase flow; particle-laden; heavy particles; light particles;

   Sammanfattning : This thesis presents the study of laminar to turbulent transition of particle laden flows. When a flow becomes turbulent, the drag increases one order of magnitude compared to a laminar flow, therefore, much research is devoted to understand and influence the transition. LÄS MER

4. 3. Boundary layer streaks as a novel laminar flow control method

   Författare :Sohrab Sattarzadeh Shirvan; Jens H. M. Fransson; Edward B. White; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; boundary layer stability; laminar to turbulent transition; laminar flow control; drag reduction; Tollmien-Schlichting waves; oblique waves; streaky boundary layers; miniature vortex generators; discrete suction;

   Sammanfattning : A novel laminar flow control based on generation of spanwise mean velocity gradients (SVG) in a flat plate boundary layer is investigated where disturbances of different types are introduced in the wall-bounded shear layer. The experimental investigations are aimed at; (i) generating stable and steady streamwise streaks in the boundary layer which set up spanwise gradients in the mean flow, and (ii) attenuating disturbance energy growth in the streaky boundary layers and hence delaying the onset of turbulence transition. LÄS MER

5. 4. On stability, transition and turbulence in three-dimensional boundary-layer flows

   Författare :Seyed Mohammd Hosseini; Ardeshir Hanifi; Spencer Sherwin; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Receptivity; stability; optimal growth; three-dimensional bound- ary layers; crossflow instability; roughness control; freestream turbulence; sec- ondary instability; transition; turbulence;

   Sammanfattning : A lot has changed since that day on December 17, 1903 when the Wright brothers made the first powered manned flight. Even though the concepts behind flying are unaltered, appearance of stat-of-the-art modern aircrafts has undergone a massive evolution. LÄS MER

7. 5. 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