Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
Results
Showing 1 to 20 of 85 for “"Shear flows"”.
-
Dynamics of Periodic Stratified Shear Flows
In questa tesi studiamo le instabilità in fluidi stratificati laminari dove la stratificazione in densità ha un effetto stabilizzante. Nonostante l idea comune che la forza d Archimede abbia un effetto stabilizzante, in alcune circostanze tale stratificazione ha mostrato di poter indurre …
-
Turbulent Molecular Mixing in Gaseous Free Shear Flows
… in this investigation span three main stages of shear layer development. Vortex mixing in the near field of an axisymmetric jet (ReD = 2300) is studied by using an acoustic pulse to obtain repeatable vortex formation and merging events. Results indicate that the mixing process is initially slow …
-
Properties of Conditional Eddies in Free Shear Flows
Large structures in two types of free turbulent flows, namely, grid turbulence and two-stream, plane mixing flow, have been investigated through studies of conditional averages. The conditional averages of interest were expected values of the instantaneous velocity and the second-order velocity …
-
Instability and Energy Growth in Stratified Shear Flows
The dynamics of stratified shear flows are extremely complex due to the interplay between shear and buoyancy effects. In addition, the breakdown from a laminar state into a turbulent one is a process that is far from completely understood, despite aspects of turbulence being studied for over a …
-
Waves and turbulence in sustained stratified shear flows
… this phenomenon by providing insight into real flows under controlled conditions. This dissertation addresses some aspects of the laboratory buoyancy-driven exchange flows through an inclined duct connecting two reservoirs containing fluids of different densities. We employ a novel experimental …
-
Linear and nonlinear dynamics in stratified shear flows
Stably stratified shear flows, in which a less dense layer of fluid lies above and moves counter to a more dense layer below, are ubiquitous in geophysical fluid dynamics. These are often found to be unstable if the non-dimensional Richardson number Ri, quantifying the strength of stratification to …
-
Momentum and scalar transport in vegetated shear flows
Environmental aquatic flows are seldom free of vegetative influence. However, the impact of submerged vegetation on the hydrodynamics and mixing processes in aquatic flows remains poorly understood. In this thesis, I present the results of laboratory experiments that describe the salient …
-
Methodologies for active control of free shear flows
… basic mechanism of the active control of free shear flows and look for new concepts in actuation methodologies. The possibility of controlling the evolution of a triangular jet is discussed in Chapter 2. The piezoceramic actuators were mounted on the flat sides of the nozzle. The flow was fully …
-
Passive Scalar Measurements In Actively Excited Free Shear Flows
… a system to measure mixing in nonreacting flows and to study the mass transfer characteristics of two actively excited turbulent jets. This thesis describes the acquisition and analysis of phase-locked concentration field data using planar Mie scattering from smoke particles and planar …
-
Model-based control of transitional and turbulent wall-bounded shear flows
University of Minnesota Ph.D. dissertation. January 2013. Major: Electrical Engineering. Advisor: Professor Mihailo R. Jovanovic. 1 computer file (PDF); xvii, 242 pages, appendices A-E.
-
Large Eddy Simulation and Analysis of Shear Flows in Complex Geometries
… is used to numerically investigate two types of shear flows in complex geometries, (i) a novel momentum driven countercurrent shear flow in dump geometry and (ii) a film cooling flow (inclined jet in crossflow). Verification of subgrid scale model is done through comparisons with measurements for …
-
Nonlinear and non-modal stability of structures evolving in shear flows
… that develop in various constant density flows. In particular, the stability of nonlinear structures which develop in rotating plane Couette flow is analyzed using Floquet theory, which allows the global stability of an important secondary nonlinear structure called a Taylor vortex to be …
-
An experimental investigation of large-scale structures in supersonic reattaching shear flows
… of large-scale structures within the shear layers, at reattachment, and in the wake region of a supersonic base flow. Single-pulse side and end views were obtained at several streamwise locations to characterize the evolution and three-dimensionality of the large-scale motions. From …
-
A Wiener Chaos Based Approach to Stability Analysis of Stochastic Shear Flows
… this end, we study the stability of stochastic shear flows, and adopt a framework based upon the Wiener Chaos expansion for efficient numerical computations. We explore the stability of stochastic Poiseuille, Couette and Blasius boundary layer type base flows, presenting stochastic results for …
-
Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows
In hypersonic flows, turbulence critically influences mass and momentum transport, mixing, heat transfer and acoustic noise generation. In contrast to incompressible flow, in high speed flows pressure is a true thermodynamic variable and flowthermodynamic interactions render the investigations …
-
Prediction of turbulent mixing at the interface of density stratified, shear flows using CFD
… simulations were performed involving stratified, shear flows that have been investigated experimentally. One set of simulations dealt with a homogeneous shear flow involving miscible fluids. The other set of simulations dealt with a developing shear layer involving immiscible fluids. The …
-
A theoretical investigation of an averaged-structure eddy viscosity model applied to turbulent shear flows
… the steady incompressible turbulent Poiseuille flows between parallel flat plates and through circular pipes. The Navier-Stokes equations are simplified and solved analytically, with the aid of Integral Transform methods and asymptotic expansions. With the appropriate numerical values for the …
-
Generalised nonlinear stability of stratified shear flows: adjoint-based optimisation, Koopman modes, and reduced models
… seeds in both vertically and horizontally sheared stratified plane Couette flow. I find that the coherent states visited by such minimal seed trajectories are significantly altered by the stratification, and so proceed to investigate these states both with generalised Koopman mode analysis …
-
Finite element solution of the Navier-Stokes equations for 3-D turbulent free shear flows
… of two and three-dimensional turbulent free shear flows. The model is derived by integrating the parabolized transport equation for the turbulence kinetic energy over the cross section of the flow. The Prandtl-Kolmogrov hypothesis is used to obtain an ordinary differential equation for the …
-
A parametric study of the hydrodynamic stability theory of 3-D compressible free shear flows
… stability problem. A parametric study of free shear flows with two or more supersonic streams is performed. Flows examined included shear layers, jets/wakes, and various geometrical combinations of these flows. The effect of Mach number on the stability characteristics of the flow is studied …
Page 1 of 5