Engineering topics

Morkovin, Mark V.

Publications and source records attributed to Morkovin, Mark V..

5 records

NASA NTRS1992

Mach number effects on free and wall turbulent structures in light of instability flow interactions

Our perception of fluid instabilities and turbulence is largely based on properties of incompressible vorticity distributions, omega, and the Biot-Savart Law of 'instantaneous' induction at distance. In high-speed shear layers it is the distribution of local angular momentum rho-omega that matters; modified interaction-induction between vortical elements is likely to take place only within relative Mach cones of influence, with acoustic time delay. This and the large mean density stratifications influence strongly instability vortex roll-ups, vortex mergings, and large-scale turbulent structures. Consequences of these observations on transition to turbulence and turbulence energetics are discussed in physical terms. Free shear layers and wall layers may require distinct M modeling.

Morkovin, Mark V.↗

NASA NTRS1990

On receptivity to environmental disturbances

The instability dehomogenization of shear-layer vorticity is addressed, and conditions for stimulation of unstable normal modes are considered with emphasis on spatially-unstable flows. Minute wall changes as an example of Tollmien-Schlichting wave forcing by sound is analyzed, rapid and moderate x-variations in mean and disturbance fields are considered, and it is pointed out that x-dependences within the whole system of a shear layer can provide one or several receptivity paths. The role of the leading edge in covered along with its idealization. Detailed validation of receptivity paths, receptivity to free-stream turbulence, and nonperiodic excitation are also discussed.

Morkovin, Mark V.↗

NASA NTRS1990

On roughness-induced transition - Facts, views, and speculations

Roughness is considered as a steady passive device, and it is shown that roughness-induced separation is specifically sensitive to unsteady environmental forcing. The two-dimensional isolated roughness causing local upstream and downstream separations is considered, along with flows associated with the two-dimensional roughness and their relevance to the problem of distributed roughness. The difference between the two-dimensional isolated roughness and a three-dimensional isolated roughness at all Reynolds numbers is underlined, and the mechanisms and parameter conditions of a sudden breakdown of hairpin eddies are discussed, as well as flows over distributed roughness.

Morkovin, Mark V.↗

NASA NTRS1988

Recent insights into instability and transition to turbulence in open-flow systems

Roads to turbulence in open-flow shear layers are interpreted as sequences of often competing instabilities. These correspond to primary and higher order restructurings of vorticity distributions which culminate in convected spatial disorder (with some spatial coherence on the scale of the shear layer) traditionally called turbulence. Attempts are made to interpret these phenomena in terms of concepts of convective and global instabilities on one hand, and of chaos and strange attractors on the other. The first is fruitful, and together with a review of mechanisms of receptivity provides a unifying approach to understanding and estimating transition to turbulence. In contrast, current evidence indicates that concepts of chaos are unlikely to help in predicting transition in open-flow systems. Furthermore, a distinction should apparently be made between temporal chaos and the convected spatial disorder of turbulence past Reynolds numbers where boundary layers and separated shear layers are formed.

Morkovin, Mark V.↗

NASA NTRS1987

Transition at hypersonic speeds

Certain conjectures on the physics of instabilities in high-speed flows are discussed and the state of knowledge of hypersonic transition summarized. The case is made for an unpressured systematic research program in this area consisting of controlled microscopic experiments, theory, and numerical simulations.

Morkovin, Mark V.↗