ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Articles  (11)
  • Journal of Fluid Mechanics. 1971; 48(2): 405-415. Published 1971 Jul 28. doi: 10.1017/s0022112071001654.  (1)
  • Journal of Fluid Mechanics. 1974; 64(2): 307-318. Published 1974 Jun 19. doi: 10.1017/s0022112074002412.  (1)
  • Journal of Fluid Mechanics. 1977; 79(4): 689. Published 1977 Mar 01. doi: 10.1017/s0022112077000391.  (1)
  • Journal of Fluid Mechanics. 1980; 101(2): 321-348. Published 1980 Nov 27. doi: 10.1017/s0022112080001681.  (1)
  • Journal of Fluid Mechanics. 1988; 191(-1): 465. Published 1988 Jun 01. doi: 10.1017/s002211208800165x.  (1)
  • Journal of Fluid Mechanics. 1991; 229(-1): 417. Published 1991 Aug 01. doi: 10.1017/s0022112091003087.  (1)
  • Journal of Fluid Mechanics. 1994; 278: 101-121. Published 1994 Nov 10. doi: 10.1017/s0022112094003630.  (1)
  • Journal of Fluid Mechanics. 1999; 378: 269-289. Published 1999 Jan 10. doi: 10.1017/s0022112098003140.  (1)
  • Journal of Fluid Mechanics. 2003; 493: 151-179. Published 2003 Oct 25. doi: 10.1017/s0022112003005718.  (1)
  • Journal of Fluid Mechanics. 2013; 728: 120-145. Published 2013 Jul 03. doi: 10.1017/jfm.2013.258.  (1)
  • Journal of Fluid Mechanics. 2016; 803: 556-590. Published 2016 Aug 30. doi: 10.1017/jfm.2016.512.  (1)
  • 2122
Collection
  • Articles  (11)
Source
Publisher
Years
Journal
Topic
  • 1
    facet.materialart.
    Unknown
    Fully coupled resonant-triad interactions in a free shear layer (1994)
    Cambridge University Press
    Details
    Publication Date: 1994-11-10
    Description: We report the results of an investigation of the weakly nonlinear evolution of a triad of waves, each slightly amplified on a linear basis, that are superimposed on a tanh y mixing layer. The triad consists of a plane wave and a pair of oblique modes that act as a subharmonic of order 1/2. The oblique modes are inclined at approximately±60° to the mean flow direction and because the resonance conditions are satisfied exactly the analysis is entirely self-consistent as an asymptotic theory. The nonlinearity first occurs within the critical layer and the initial interaction is of the parametric resonance type. This produces faster than exponential growth of the oblique waves, behaviour observed recently in the experiments of Corke& Kusek (1993). The critical-layer dynamics lead subsequently to coupled integro-differential equations governing the amplitude evolution and, as first shown in related work by Goldstein& Lee (1992) on boundary layers in an adverse pressure gradient, these equations develop singularities in a finite time. © 1994, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 2
    facet.materialart.
    Unknown
    A numerical investigation of resonant interactions in adverse-pressure-gradient boundary layers (1999)
    Cambridge University Press
    Details
    Publication Date: 1999-01-10
    Description: We present direct numerical simulations of the spatial development of normal mode perturbations to boundary layers with Falkner-Skan velocity profiles. Values of the pressure gradient parameter considered range from very small, i.e. nearly flat-plate conditions, to relatively large values corresponding to incipient separation. In almost all cases, we find that the most effective perturbation is one composed of a plane wave and a pair of oblique waves inclined at equal and opposite angles to the primary flow direction. The frequency of the oblique waves is half that of the fundamental plane wave and because the conditions for resonance are satisfied exactly, all modes share a common critical layer, thus facilitating a strong interaction. The oblique waves initially undergo a parametric type of subharmonic resonance, but in accordance with recent analyses of non-equilibrium critical layers, the system subsequently becomes fully coupled. From that point on, the amplification of all modes, including the plane wave, substantially exceeds the predictions of linear stability theory. Good agreement is obtained with the experimental small pressure gradient results of Corke & Gruber (1996). Our growth rates are slightly larger owing to slight differences in initial conditions (e.g. the angle of inclination of the oblique waves). The spectral element method was used to discretize the Navier-Stokes equations and the preconditioned conjugate gradient method was used to solve the resulting system of algebraic equations. At the inflow boundary, Orr-Sommerfeld modes were employed to provide the initial forcing, whereas the buffer domain technique was used at the outflow boundary to prevent convective wave reflection or upstream propagation of spurious information.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 3
    facet.materialart.
    Unknown
    Nonlinear critical-layer evolution of a forced gravity wave packet (2003)
    Cambridge University Press
    Details
    Publication Date: 2003-10-25
    Description: In this paper, numerical simulations are presented of the nonlinear critical-layer evolution of a forced gravity wave packet in a stratified shear flow. The wave packet, localized in the horizontal direction, is forced at the lower boundary of a two-dimensional domain and propagates vertically towards the critical layer. The wave-mean-flow interactions in the critical layer are investigated numerically and contrasted with the results obtained using a spatially periodic monochromatic forcing. With the horizontally localized forcing, the net absorption of the disturbance at the critical layer continues for large time and the onset of the nonlinear breakdown is delayed compared with the case of monochromatic forcing. There is an outward flux of momentum in the horizontal direction so that the horizontal extent of the packet increases with time. The extent to which this happens depends on a number of factors including the amplitude and horizontal length of the forcing. It is also seen that the prolonged absorption of the disturbance stabilizes the solution to the extent that it is always convectively stable; the local Richardson number remains positive well into the nonlinear regime. In this respect, our results for the localized forcing differ from those in the case of monochromatic forcing where significant regions with negative Richardson number appear.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 4
    facet.materialart.
    Unknown
    Inviscid instability of an unbounded heterogeneous shear layer (1971)
    Cambridge University Press
    Details
    Publication Date: 1971-07-28
    Description: Stability curves are computed for both spatially and temporally growing disturbances in a stratified mixing layer between two uniform streams. The low Froude number limit, in which the effects of buoyancy predominate, and the high Froude number limit, in which the effects of density variation are manifested by the inertial terms of the vorticity equation, are considered as limiting cases. For the buoyant case, although the spatial growth rates can be predicted reasonably well by suitable use of the results for temporal growth, spatially growing disturbances appear to have high group velocities near the lower cutoff wave-number. For the inertial case, it is demonstrated that density variations can be destabilizing. More precisely, when the stream with the higher velocity has the lower density, both the wave-number range of unstable disturbances and the maximum spatial growth rate are increased relative to the case of homogeneous flow. Finally, it is shown how the growth rate of the most unstable wave in the inertial case diminishes as buoyancy becomes important. © 1971, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 5
    facet.materialart.
    Unknown
    Weakly nonlinear stability of a viscous free shear layer (1977)
    Cambridge University Press
    Details
    Publication Date: 1977-03-01
    Description: Numerical calculations of the Landau constant are presented for the case of a shear layer of finite Reynolds number, having the velocity profile [formula omitted]. It is found that this parameter has a strong dependence on the Reynolds number for Re ⩽ 100. In particular, the Landau constant is reduced by 43% from its inviscid value when Re = 40, the latter value being typical of many experiments. This percentage, however, is based upon a calculation in which the mean-flow distortion has been neglected. A rough estimate of the latter effect indicates that it could possibly increase the value of the Landau constant sufficiently that the net influence of a finite Reynolds number would be of a smaller magnitude. © 1977, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 6
    facet.materialart.
    Unknown
    Elliptical instability of the Moore–Saffman model for a trailing wingtip vortex (2016)
    Cambridge University Press
    Details
    Publication Date: 2016-08-30
    Description: In this paper, we investigate the elliptical instability exhibited by two counter-rotating trailing vortices. This type of instability can be viewed as a resonance between two normal modes of a vortex and an external strain field. Recent numerical investigations have extended earlier results that ignored axial flow to include models with a simple wake-like axial flow such as the similarity solution found by Batchelor (J. Fluid Mech., vol. 20, 1964, pp. 645-658). We present herein growth rates of elliptical instability for a family of velocity profiles found by Moore & Saffman (Proc. R. Soc. Lond. A, vol. 333, 1973, pp. 491-508). These profiles have a parameter that depends on the wing loading. As a result, unlike the Batchelor vortex, they are capable of modelling both the jet-like and the wake-like axial flow present in a trailing vortex at short and intermediate distances behind a wingtip. Direct numerical simulations of the linearized Navier-Stokes equations are performed using an efficient spectral method in cylindrical coordinates developed by Matsushima & Marcus (J. Comput. Phys., vol. 53, 1997, pp. 321-345). We compare our results with those for the Batchelor vortex, whose velocity profiles are closely approximated as the wing loading parameter approaches 1. An important conclusion of our investigation is that the stability characteristics vary considerably with and, a parameter measuring the strength of the mean axial velocity component. In the case of an elliptically loaded wing, we find that the instability growth rates are up to 50 % greater than those for the Batchelor vortex. Our results demonstrate the significant effect of the distribution and intensity of the axial flow on the elliptical instability of a trailing vortex. © 2016 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 7
    facet.materialart.
    Unknown
    A study of singular modes associated with over-reflection and related phenomena (2013)
    Cambridge University Press
    Details
    Publication Date: 2013-07-03
    Description: This paper describes an investigation of the linear, diffusive critical layer for shear flows whose inviscid neutral modes have an algebraic branch point. As examples of flows exhibiting such singular behaviour, we treat both stratified shear flows and non-axisymmetric modes on vortices. For the stratified case, the coupled vorticity and energy equations are solved numerically. In this way, the density perturbation, which is unbounded in the absence of diffusion, is determined directly. As an example featuring a vortex, we consider helical modes on a modified Lamb-Oseen vortex whose velocity profile is perturbed in such a way that linear instability is possible. Both the axial and azimuthal velocity perturbations in the critical layer are determined. A characteristic shared by all the above problems is that they involve eigenfunctions that are oscillatory in some region. For forced waves in a stably stratified shear flow, we consider a larger range of parameters than previous investigators. We also examine some experiments and find that the Reynolds stress is sensitive to the actual density profile in the region between a wavy wall providing the forcing and the critical layer. For the stratified shear flows without forcing, much smaller Richardson numbers are involved and the modes considered are over-reflecting. For an unbounded y mixing layer, we show that the Reynolds stress for a neutral mode must jump across the critical layer. With the presence of a horizontal boundary beneath the shear layer, on the other hand, over-reflection can occur, with the Reynolds stress vanishing on either side of the critical layer. In all cases, the variation of the Reynolds stress across the critical layer is determined. © 2013 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 8
    facet.materialart.
    Unknown
    Instability of rigidly rotating flows to non-axisymmetric disturbances (1974)
    Cambridge University Press
    Details
    Publication Date: 1974-06-19
    Description: An investigation of the hydrodynamic stability of swirling flows having arbitrary Rossby numbers is described. A necessary condition for instability is derived for rigidly rotating flows and this condition is further refined in the specific case of a parabolic axial flow. Numerical results are presented for two azimuthal wave-numbers corresponding to the maximum growth rates of unstable perturbations as a function of Rossby number. It is found that the largest growth rates occur when the Rossby number is O(1) and that instability persists for surprisingly large values of this parameter. Previous explanations of the instability mechanism are discussed and it is concluded that these are only adequate in the limit of small Rossby number. © 1974, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 9
    facet.materialart.
    Unknown
    Long nonlinear waves in stratified shear flows (1980)
    Cambridge University Press
    Details
    Publication Date: 1980-11-27
    Description: The propagation of finite-amplitude internal waves in a shear flow is considered for wavelengths that are long compared to the shear-layer thickness. Both singular and regular modes are investigated, and the equation governing the amplitude evolution is derived. The theory is generalized to allow for a radiation condition when the region outside the stratified shear layer is unbounded and weakly stratified. In this case, the evolution equation contains a damping term describing energy loss by radiation which can be used to estimate the persistence of solitary waves or nonlinear wave packets in realistic environments. A continuous three-layer model is studied in detail and closed-form expressions are obtained for the phase speed and the coefficients of the nonlinear and dispersive terms in the amplitude equation as a function of Richardson number. © 1980, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
  • 10
    facet.materialart.
    Unknown
    Barotropic instability of the Bickley jet (1991)
    Cambridge University Press
    Details
    Publication Date: 1991-08-01
    Description: The linear stability of the zonal shear flow ū = -sech2 y is investigated in the framework of the beta-plane approximation. This retrograde jet is known to be more unstable than its eastward-propagating counterpart and has some surprising characteristics. First, this is a rare example of a flow in which barotropically unstable modes occur that do not have a critical point. Secondly, singular neutral modes exist in which the critical point occurs at the centre of the jet, where ūc = 0. It is shown in this paper that such singular modes form part of the stability boundary both for the varicose mode and also for the radiating sinuous mode. © 1991, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    PAPER CURRENT
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...