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Michael T. Montgomery - One of the best experts on this subject based on the ideXlab platform.
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hurricane Boundary Layer theory
Quarterly Journal of the Royal Meteorological Society, 2010Co-Authors: Roger K Smith, Michael T. MontgomeryAbstract:In the light of the plethora of definitions for the hurricane Boundary Layer, we advocate a dynamical definition based on the distribution of agradient flow. We seek also to clarify the fundamental role of the Boundary Layer in the hurricane intensification process. In particular, we contrast the differences between unsteady Boundary Layers that are able to facilitate the spin-up of the vortex above and steady Boundary Layers that cannot. If slaved to the time-dependent vortex aloft, the latter can spin up the interior vortex only indirectly by changing its thermodynamic properties through vertical advection of these from below and adjustment to thermal wind balance. These differences are highlighted by an analytical demonstration that the application of a zero-vertical-gradient condition on velocity above a steady Boundary Layer does not provide a direct means of allowing the Boundary Layer to determine the flow in the interior vortex. This result assumes that frictional forces are negligible at this Boundary. Finally, echoing a few previous insights, we question the applicability of conventional Boundary-Layer theory at radii of strong ascent into the eyewall, where the flow is akin to that of separation in aerodynamic Boundary Layers. Copyright c � 2010 Royal Meteorological Society
Anatoly I. Ruban - One of the best experts on this subject based on the ideXlab platform.
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Oxford Scholarship Online - Classical Boundary-Layer Theory
Oxford Scholarship Online, 2018Co-Authors: Anatoly I. RubanAbstract:Chapter 1 discusses the flows that can be described in the framework of Prandtl’s 1904 classical Boundary-Layer theory, including the Blasius Boundary Layer on a flat plate and the Falkner–Skan solutions for the Boundary Layer on a wedge surface. It presents Schlichting’s solution for the laminar jet and Tollmien’s solution for the viscous wake. These are followed by analysis of Chapman’s shear Layer performed with the help of Prandtl’s transposition theorem. It also considers the Boundary Layer on the surface of a fast rotating cylinder with the purpose of linking the circulation around the cylinder with the speed of its rotation. It concludes discussion of the classical Boundary-Layer theory with analysis of compressible Boundary Layers, including the interactive Boundary Layers in hypersonic flows.
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Oxford Scholarship Online - Boundary-Layer Separation
Oxford Scholarship Online, 2018Co-Authors: Anatoly I. RubanAbstract:Chapter 2 discusses the experimental observations of the Boundary-Layer separation in subsonic and supersonic flows that lead to a formulation of the concept of viscous-inviscid interaction. It then turns to the so-called ‘self-induced separation’ of the Boundary Layer in supersonic flows. This theory is formulated based on the asymptotic analysis of the Navier–Stokes equations at large values of the Reynolds number. As a part of the flow analysis, this chapter also introduces the ‘triple-deck model’. It then shows how this model may be used to describe the classical problem of the Boundary-Layer separation in an incompressible fluid flow past a circular cylinder.
Roger K Smith - One of the best experts on this subject based on the ideXlab platform.
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hurricane Boundary Layer theory
Quarterly Journal of the Royal Meteorological Society, 2010Co-Authors: Roger K Smith, Michael T. MontgomeryAbstract:In the light of the plethora of definitions for the hurricane Boundary Layer, we advocate a dynamical definition based on the distribution of agradient flow. We seek also to clarify the fundamental role of the Boundary Layer in the hurricane intensification process. In particular, we contrast the differences between unsteady Boundary Layers that are able to facilitate the spin-up of the vortex above and steady Boundary Layers that cannot. If slaved to the time-dependent vortex aloft, the latter can spin up the interior vortex only indirectly by changing its thermodynamic properties through vertical advection of these from below and adjustment to thermal wind balance. These differences are highlighted by an analytical demonstration that the application of a zero-vertical-gradient condition on velocity above a steady Boundary Layer does not provide a direct means of allowing the Boundary Layer to determine the flow in the interior vortex. This result assumes that frictional forces are negligible at this Boundary. Finally, echoing a few previous insights, we question the applicability of conventional Boundary-Layer theory at radii of strong ascent into the eyewall, where the flow is akin to that of separation in aerodynamic Boundary Layers. Copyright c � 2010 Royal Meteorological Society
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a simple model of the hurricane Boundary Layer
Quarterly Journal of the Royal Meteorological Society, 2003Co-Authors: Roger K SmithAbstract:A simple, steady, moist, axisymmetric, constant-depth, slab model for the hurricane Boundary Layer is investigated. High-resolution solutions of the Boundary-Layer equations are obtained by integrating inwards from some large radius, at which it is assumed that geostrophic balance and convective–radiative balance exist. In all the solutions obtained, the tangential wind speed in the Boundary Layer approaches that above the Boundary Layer in the inner-core region and the maximum wind speed in the Boundary Layer is comparable with, or even marginally higher than that above. A new feature of one of the solutions described is the existence of spatial oscillations in vertical velocity at the top of the Boundary Layer, inside the radius of maximum tangential wind speed. These oscillations may be interpreted as frictionally damped inertial waves. They are accompanied by annular regions in which the tangential flow alternates between supergradient and subgradient. The existence of Boundary-Layer-induced oscillations in vertical velocity in reality would have implications for the organization of convection in the core region of a hurricane. It is shown that an approximation to determine the radial flow in the Boundary Layer suggested by Willoughby overestimates the vertical motion at the top of the Boundary Layer by a factor of about two, but the analysis leads us to question the utility of the approximation. We investigate also the thermodynamic structure of the Boundary Layer and the radial distribution of surface fluxes for vortices with the same maximum tangential wind speed above the Boundary Layer and the same radius of maximum wind (RMW), but having different widths. It is found that the equivalent potential temperature (θe) in the Boundary Layer continues to increase with decreasing radius inside the RMW. Moreover, the negative radial gradient of θe in the inner-core region, which is related to that of virtual temperature above the Boundary Layer in the eyewall region, is relatively insensitive to the vortex width, but the maximum values of θe increase with the width. The strength and radial distribution of the latent-heat flux is insensitive to the vortex width in the inner-core region, but varies markedly with width in the outer part of the vortex. Realistic radial distribution of relative humidity are obtained only when shallow convection is represented in the model. The inclusion of dissipative heating in the thermodynamic equation leads to an increase in θe of the order of 1.5 K in the inner-core region of the vortex and to a reduction in the Boundary-Layer relative humidity of 5%. Copyright © 2003 Royal Meteorological Society
J D A Walker - One of the best experts on this subject based on the ideXlab platform.
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vortex induced Boundary Layer separation part 2 unsteady interacting Boundary Layer theory
Journal of Fluid Mechanics, 1991Co-Authors: Vallorie J Peridier, F T Smith, J D A WalkerAbstract:The unsteady Boundary Layer induced by the motion of a rectilinear vortex above an infinite plane wall is calculated using interacting Boundary-Layer methods. The Boundary-Layer solution is computed in Lagrangian variables since it is possible to compute the flow evolution accurately in this formulation even when an eruption starts to evolve. Results are obtained over a range of Reynolds numbers, Re. For the limit problem Re - infinity (studied in Part 1), a singularity develops in the non-interacting Boundary-Layer solution at finite time. The present results show that the interacting Boundary-Layer calculations also terminate in a singularity at a time which is earlier than in the limit problem and which decreases with decreasing Reynolds number. The computed results are compared with the length-and timescales predicted by recent asymptotic theories and are found to be in excellent agreement. See also previous abstract.
Roger L. Kimmel - One of the best experts on this subject based on the ideXlab platform.
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On hypersonic Boundary-Layer stability
30th Aerospace Sciences Meeting and Exhibit, 1992Co-Authors: Kenneth F. Stetson, Roger L. KimmelAbstract:This paper reviews experimental hypersonic BoundaryLayer stability results obtained using hot-wire anemometry techniques. Data are obtained at a freestream Mach number of 8 on water-cooled and uncooled 7-degree half angle cones and on a water-cooled cylinder. A limited amount of cone data were obtained at M, = 6 . It is shown that one can not just extend subsonic and supersonic stability concepts and transition data to hypersonic Mach numbers. Hypersonic Boundary-Layer transition phenomena have several unique features and the topics must be treated independently. In low speed Boundary Layers one is accustomed to thinking of the vorticity instability mode which produces low frequency, low amplitude velocity fluctuations. A unique feature of a hypersonic Boundary Layer is the presence of the higher instability modes, the Mack modes. These instabilities v produce high frequency, large amplitude density fluctuations which can dominate the transition process. Some hypersonic trends are different from lower Mach number trends. Surface temperature effect is a good example. Cooling the surface stabilizes low Mach number Boundary Layers, but can destabilize a hypersonic Boundary Layer. Many of the parametric effects are very sensitive to Mach number. For example, it is shown that a small nosetip bluntness can completely dominate the stability of a hypersonic Boundary Layer, resulting in very large critical Reynolds numbers. This paper reviews general hypersonic stability characteristics, comparisons with theory, several parametric effects, and cone versus planar Boundary-Layer stability.
