The Stability of a Viscous Heterogeneous Shear Flow

The Stability of a Viscous Heterogeneous Shear Flow
Author: Frank D. Hains
Publisher:
Total Pages: 37
Release: 1968
Genre:
ISBN:

A numerical method is used to compute the stability of a shear layer embedded between two homogeneous fluid regions of different densities that are moving at uniform but different velocities. The mean flow is specified by a hyperbolic tangent velocity profile and an exponential of a hyperbolic tangent density profile. Numerical results are presented that show the changes in the stability of the layer with the Reynolds number, Froude number, wavenumber of the disturbance, and the gradients of shear and density. Two modes of instability are found: one propagates upstream relative to the moving fluid, the other propagates downstream at a velocity that is always less than the average of the two outer regions. Viscosity tends to stabilize waves that are already stable and to destabilize waves that are unstable. The neutral stability curves appear to have only one branch; therefore, no critical Reynolds numbers were found. Gravity tends to stabilize one mode and to destabilize the other; but when gravity forces are very large, both modes are stabilized. One mode was unstable when the minimum Richardson number across the shear layer exceeded 1/4; therefore, the critical Richardson number for a viscous fluid must be larger than that for an inviscid fluid. (Author).

Stability and Transition in Shear Flows

Stability and Transition in Shear Flows
Author: Peter J. Schmid
Publisher: Springer Science & Business Media
Total Pages: 561
Release: 2012-12-06
Genre: Science
ISBN: 1461301858

A detailed look at some of the more modern issues of hydrodynamic stability, including transient growth, eigenvalue spectra, secondary instability. It presents analytical results and numerical simulations, linear and selected nonlinear stability methods. By including classical results as well as recent developments in the field of hydrodynamic stability and transition, the book can be used as a textbook for an introductory, graduate-level course in stability theory or for a special-topics fluids course. It is equally of value as a reference for researchers in the field of hydrodynamic stability theory or with an interest in recent developments in fluid dynamics. Stability theory has seen a rapid development over the past decade, this book includes such new developments as direct numerical simulations of transition to turbulence and linear analysis based on the initial-value problem.

NOTE ON A HETEROGENEOUS SHEAR FLOW.

NOTE ON A HETEROGENEOUS SHEAR FLOW.
Author: John W. Miles
Publisher:
Total Pages: 6
Release: 1964
Genre:
ISBN:

Goldstein has considered the stability of a shear layer within which the velocity and the density vary linearly and outside which they are constant. Rayleigh had found that the corresponding, homogeneous shear flow is unstable in and only in a finite band of wave-numbers. Goldstein concluded that a small density gradient renders the flow unstable for all wave-numbers. This conclusion appears to depend on the acceptance of all possible branches of a multi-valued eigenvalue equation, and it is shown that the principal branch of this eigenvalue equation yields one and only one unstable mode if and only if the wavenumber lies in a band that decreases from Rayleigh's band to zero as the Richardson number increases from 0 to 1/4. (Author).

Physics of Transitional Shear Flows

Physics of Transitional Shear Flows
Author: Andrey V. Boiko
Publisher: Springer Science & Business Media
Total Pages: 286
Release: 2011-09-15
Genre: Science
ISBN: 9400724985

Starting from fundamentals of classical stability theory, an overview is given of the transition phenomena in subsonic, wall-bounded shear flows. At first, the consideration focuses on elementary small-amplitude velocity perturbations of laminar shear layers, i.e. instability waves, in the simplest canonical configurations of a plane channel flow and a flat-plate boundary layer. Then the linear stability problem is expanded to include the effects of pressure gradients, flow curvature, boundary-layer separation, wall compliance, etc. related to applications. Beyond the amplification of instability waves is the non-modal growth of local stationary and non-stationary shear flow perturbations which are discussed as well. The volume continues with the key aspect of the transition process, that is, receptivity of convectively unstable shear layers to external perturbations, summarizing main paths of the excitation of laminar flow disturbances. The remainder of the book addresses the instability phenomena found at late stages of transition. These include secondary instabilities and nonlinear features of boundary-layer perturbations that lead to the final breakdown to turbulence. Thus, the reader is provided with a step-by-step approach that covers the milestones and recent advances in the laminar-turbulent transition. Special aspects of instability and transition are discussed through the book and are intended for research scientists, while the main target of the book is the student in the fundamentals of fluid mechanics. Computational guides, recommended exercises, and PowerPoint multimedia notes based on results of real scientific experiments supplement the monograph. These are especially helpful for the neophyte to obtain a solid foundation in hydrodynamic stability. To access the supplementary material go to extras.springer.com and type in the ISBN for this volume.