Laboratory measurements of the drag force on a family of two-dimensional ice keel models in a two-layer flow

1996 ◽  
Vol 22 ◽  
pp. 133
Author(s):  
H Pite
Keyword(s):  
Drag Force ◽  
Two Dimensional ◽  
Laboratory Measurements ◽  
Layer Flow

Non-hydrostatic effects in layered shallow water flows

1998 ◽  
Vol 355 ◽  
pp. 1-16 ◽  
Author(s):  
DAVID Z. ZHU ◽  
GREGORY A. LAWRENCE
Keyword(s):  
Single Layer ◽  
Homogeneous Layer ◽  
Two Dimensional ◽  
Laboratory Measurements ◽  
One Dimensional ◽  
Water Flows ◽  
Shallow Water Flows ◽  
Hydraulic Theory ◽  
Layer Flow ◽  
New Equation

This paper develops a one-dimensional extension to classical layered hydraulics that incorporates non-hydrostatic effects. General results for a homogeneous layer in a multi-layer steady flow are applied to single- and two-layer flow over a two-dimensional sill. The equation obtained for single-layer flows is the same as that obtained by Naghdi & Vongsarnpigoon (1986) using the direct theory of constrained fluid sheets, and compares very well with the laboratory measurements of Sivakumaran et al. (1983). The new equation derived for two-layer flows provides excellent agreement with the laboratory measurements of Lawrence (1993). Accurate solutions are obtained for a regime of two-layer flow whose behaviour cannot be explained, even qualitatively, using classical hydraulic theory.

On Numerical Prediction of the Stability of Hypersonic Boundary-Layer Flow Over a Row of Microcavities

2003 ◽  
Author(s):  
Vassilios Theofilis ◽  
Michel O. Deville ◽  
Peter W. Duck ◽  
Alexander Fedorov
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Flow Instability ◽  
Viscous Sublayer ◽  
Hypersonic Boundary Layer ◽  
Two Dimensional ◽  
Flow Stabilization ◽  
Two Dimensional Flow ◽  
Dimensional Boundary ◽  
Layer Flow

This paper is concerned with the structure of steady two–dimensional flow inside the viscous sublayer in hypersonic boundary–layer flow over a flat surface in which microscopic cavities (‘microcavities’) are embedded. Such a so–called Ultra Absorptive Coating (UAC) has been predicted theoretically [1] and demonstrated experimentally [2] to stabilize passively hypersonic boundary–layer flow. In an effort to further quantify the physical mechanism leading to flow stabilization, this paper focuses on the nature of the basic flows developing in the configuration in question. Direct numerical simulations are performed, addressing firstly steady flow inside a singe microcavity, driven by a constant shear, and secondly a model of a UAC surface in which the two–dimensional boundary layer over a flat plate and a minimum nontrivial of two microcavities embedded in the wall are solved in a coupled manner. The influence of flow– and geometric parameters on the obtained solutions is illustrated. Based on the results obtained, the limitations of currently used theoretical methodologies for the description of flow instability are identified and suggestions for the improved prediction of the instability characteristics of UAC surfaces are discussed.

Two-dimensional global low-frequency oscillations in a separating boundary-layer flow

2008 ◽  
Vol 614 ◽  
pp. 315-327 ◽  
Author(s):  
UWE EHRENSTEIN ◽  
FRANÇOIS GALLAIRE
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Perturbation Analysis ◽  
Boundary Layer Flow ◽  
Stokes Equations ◽  
Low Frequency ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Optimal Perturbation ◽  
Layer Flow

A separated boundary-layer flow at the rear of a bump is considered. Two-dimensional equilibrium stationary states of the Navier–Stokes equations are determined using a nonlinear continuation procedure varying the bump height as well as the Reynolds number. A global instability analysis of the steady states is performed by computing two-dimensional temporal modes. The onset of instability is shown to be characterized by a family of modes with localized structures around the reattachment point becoming almost simultaneously unstable. The optimal perturbation analysis, by projecting the initial disturbance on the set of temporal eigenmodes, reveals that the non-normal modes are able to describe localized initial perturbations associated with the large transient energy growth. At larger time a global low-frequency oscillation is found, accompanied by a periodic regeneration of the flow perturbation inside the bubble, as the consequence of non-normal cancellation of modes. The initial condition provided by the optimal perturbation analysis is applied to Navier–Stokes time integration and is shown to trigger the nonlinear ‘flapping’ typical of separation bubbles. It is possible to follow the stationary equilibrium state on increasing the Reynolds number far beyond instability, ruling out for the present flow case the hypothesis of some authors that topological flow changes are responsible for the ‘flapping’.

Boundary-Layer Flow Between the Attachment Lines on a Flat Plate Delta Wing at Incidence

1962 ◽  
Vol 13 (1) ◽  
pp. 1-16
Author(s):  
J. C. Cooke
Keyword(s):  
Boundary Layer ◽  
Delta Wing ◽  
Three Dimensional ◽  
External Flow ◽  
Two Dimensional ◽  
Conical Flow ◽  
Slender Body Theory ◽  
Layer Flow ◽  
Body Theory ◽  
Transition Fronts

SummaryA three-dimensional laminar-boundary-layer calculation is carried out over the area concerned. The external flow is simplified, being calculated by slender-body theory assuming conical flow, with two point vortices above the wing, their positions and strength being determined by experiment. Attempts are made to draw transition fronts both for two-dimensional and sweep instability from this calculation. The combination of these gives fronts similar to those observed in some experiments. Because there is little or no pressure gradient over the area in question it is suggested that it is a region where distributed suction might usefully be applied in order to maintain laminar flow and reduce drag.

An Energy-Based Similarity Subgrid-Scale Model in Two-Dimensional Planar Shear Flow

2013 ◽  
Vol 694-697 ◽  
pp. 594-600
Author(s):  
Yu Xuan Zhang ◽  
Song Ping Wu
Keyword(s):  
Shear Flow ◽  
Scale Model ◽  
Two Dimensional ◽  
Subgrid Scale ◽  
Planar Shear ◽  
New Type ◽  
Subgrid Scale Model ◽  
Layer Flow ◽  
Refined Grid ◽  
Dissipative Scale

A new type of similarity subgrid-scale (SGS) model which based on energy and dissipative scale isotropy assumption is presented. This model combines the advantages of traditional Smagorinsky SGS model with similarity SGS model. And a two-dimensional shear layer flow is simulated using refined grid result as a standard and comparing witch LES method including multiple SGS models. The results indicate that the result of SIM model much approximates to refined grid result than other SGS models.

Free Convection Thermal Interaction Between 2D Components Mounted on a Vertically Oriented PCB

2002 ◽  
Author(s):  
D. Newport ◽  
T. Dalton ◽  
M. Davies
Keyword(s):  
Boundary Layer ◽  
Effective Conductivity ◽  
Ball Grid Array ◽  
Velocity Fields ◽  
Two Dimensional ◽  
Thermal Interaction ◽  
Trade Off ◽  
Layer Flow ◽  
Digital Moiré ◽  
Temperature And Velocity Fields

In this paper, measurements are presented of the temperature and velocity fields about two PCBs, with an array of five equally spaced two dimensional ribs. The ribs are two dimensional approximations of the Super Ball Grid Array (SuperBGA) package from Amkor electronics. The temperature and Nusselt number distributions are measured using Digital Moire´ Subtraction Interferometry and PIV is used to measure the velocity field. The effect of substrate conductivity is examined, and the level of thermal interaction is quantified. It is found that substrate conductivity significantly alters the induced boundary layer flow and also the recirculating vortex structure external to it. It is also found that there is a trade-off between a downstream component being heated by the thermal energy of the plume from a lower component, and cooled by the kinetic energy of that plume. The spacing to length ratio, above which the cooling effect is greater, is three for components mounted on a board with a high effective conductivity (15 W/m K). The ratio is greater than three for PCBs with lower effective conductivities. Previous work in the literature indicates a ratio greater than four for components mounted flush with an adiabatic substrate.

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