Parabolized stability equations (PSE) have opened new avenues to the analysis of the streamwise growth of linear and nonlinear disturbances in slowly varying shear flows such as boundary layers, jets, and far wakes. Growth mechanisms include both algebraic transient growth and exponential growth through primary and higher instabilities. In contrast to the eigensolutions of traditional linear stability equations, PSE solutions incorporate inhomogeneous initial and boundary conditions as do numerical solutions of the Navier-Stokes equations, but they can be obtained at modest computational expense. PSE codes have developed into a convenient tool to analyze basic mechanisms in boundary-layer flows. The most important area of application, however, is the use of the PSE approach for transition analysis in aerodynamic design. Together with the adjoint linear problem, PSE methods promise improved design capabilities for laminar flow control systems.

Parabolized stability equations

The effect of roughness on hypersonic boundarylayer transition has been studied for three primary purposes: to trip a laminar layer to turbulence, to determine whether naturally occurring roughness is expected to cause early transition, and to determine the largest allowable roughness that will not affect the location of transition. Roughness is often divided into two classes: isolated roughness in which each protuberance can be considered separately, and distributed roughness similar to sandpaper, in which the roughness elements are many and are not considered separately. The effects of roughness on hypersonic transition are reviewed, considering the physics of the process, known parametric effects, some of the common correlations, and a few case studies. The three or more modes by which roughness can affect transition are outlined. At hypersonic edge Mach nunbers, it requires very large roughness heights to affect transition. Various correlations are often used to estimate the effect of roughness; several of these are described, although none provide good agreement with all the data.

Effects of Roughness on Hypersonic Boundary-Layer Transition

The laminar-turbulent transition zone in the boundary layer

The mechanisms of the relaminarization of turbulent flows are investigated with a view to establishing any general principles that might govern them. Three basic archetypes of reverting flows are considered: the dissipative type, the absorptive type, and the Richardson type exemplified by a turbulent boundary layer subjected to severe acceleration. A number of other different reverting flows are then considered in the light of the analysis of these archetypes, including radial Poiseuille flow, convex boundary layers, flows reverting by rotation, injection, and suction, as well as heated horizontal and vertical gas flows. Magnetohydrodynamic duct flows are also examined. Applications of flow reversion for turbulence control are discussed.

Relaminarization of fluid flows

: The review report represents an attempt to evaluate critically the available data on high-speed boundary layer transition to turbulence and to interpret the apparent agreements and contradictions within some rational framework. Special attention was paid to the more documentable discrepancies between reported results as touchstones of conceptual models and instability theories. Experiments with 'microscopic' information are used as backbone of conceptual models, both linear and nonlinear. Linear instability results are used as a point of departure for the examination of current controversial questions of transition reversal with cooling, unit Reynolds number effect, effect of aerodynamic noise in supersonic wind tunnels, et.

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Critical evaluation of transition from laminar to turbulent shear layers with emphasis on hypersonically traveling bodies

/pdf/investigations-on-laminar-boundary-layer-stability-and-1fvuphmibk.pdf

Hans W Liepmann

Papers

Investigations on laminar boundary-layer stability and transition on curved boundaries