bluuebunny/crossref_metadata_2025 huggingface dataset:
Passive scalar anisotropy in a heated turbulent wake: new observations and implications for large-eddy simulations
Authors: KANG HYUNG SUK , MENEVEAU CHARLES
Published: July 2002

The effects of passive scalar anisotropy on subgrid-scale (SGS) physics and modelling
for large-eddy simulations are studied experimentally. Measurements are performed
across a moderate Reynolds number wake flow generated by a heated cylinder,
using an array of four X-wire and four cold-wire probes. By varying the separation
distance among probes in the array, we obtain filtered and subgrid quantities at three
different filter sizes. We compute several terms that comprise the subgrid dissipation
tensor of kinetic energy and scalar variance and test for isotropic behaviour, as a
function of filter scale. We find that whereas the kinetic energy dissipation tensor
tends towards isotropy at small scales, the SGS scalar-variance dissipation remains
anisotropic independent of filter scale. The eddy-diffusion model predicts isotropic
behaviour, whereas the nonlinear (or tensor eddy diffusivity) model reproduces the
correct trends, but overestimates the level of scalar dissipation anisotropy. These
results provide some support for so-called mixed models but raise new questions
about the causes of the observed anisotropy.
Mode interactions in an enclosed swirling flow:

a double Hopf bifurcation between

azimuthal wavenumbers 0 and 2
Authors: MARQUES F. , LOPEZ J. M. , SHEN J.
Published: July 2002

A double Hopf bifurcation has been found of the flow in a cylinder driven by the

rotation of an endwall. A detailed analysis of the multiple solutions in a large region of

parameter space, computed with an efficient and accurate three-dimensional Navier-Stokes solver, is presented. At the double Hopf point, an axisymmetric limit cycle

and a rotating wave bifurcate simultaneously. The corresponding mode interaction

generates an unstable two-torus modulated rotating wave solution and gives a wedge-shaped region in parameter space where the two periodic solutions are both stable.

By exploring in detail the three-dimensional structure of the flow, we have identified

the two mechanisms that compete in the neighbourhood of the double Hopf point.

Both are associated with the jet that is formed when the Ekman layer on the rotating

endwall is turned by the stationary sidewall.
On the vibrational convective instability of a horizontal,

binary-mixture layer with Soret effect
Authors: GERSHUNI G. Z. , KOLESNIKOV A. K. , LEGROS J.-C. , MYZNIKOVA B. I.
Published: July 2002

A theoretical examination is made of the mechanical

quasi-equilibrium stability of a horizontal, binary-mixture layer

with Soret effect in the presence of a high-frequency vibrational

field. The boundaries of the layer are assumed to be rigid,

isothermal and impermeable. The axis of vibration is longitudinal.

The study is based on the system of equations describing the

behaviour of mean fields. The conditions of quasi-equilibrium are

formulated. A linear stability analysis for normal modes is carried

out. In the limit of long-wave disturbances the regular perturbation

method is used with the wavenumber as a small parameter. For the case

of an arbitrary wavenumber, the calculations are made using straight

forward numerical integration. The boundaries of stability and the

critical disturbance characteristics are determined for

representative parameter values. Different instability mechanism and

forms are discussed.
Screech tones from rectangular jets with spanwise oblique

shock-cell structures
Authors: RAMAN GANESH
Published: July 2002

Understanding screech is especially important for the design

of advanced aircraft because screech can cause sonic fatigue failure

of aircraft structures. Although the connection between shock-cell

spacing and screech frequency is well understood, the relation

between non-uniformities in the shock-cell structures and the

resulting amplitude, mode, and steadiness of screech have remained

unexplored. This paper addresses the above issues by intentionally

producing spanwise (larger nozzle dimension) variations in the

shock-cell structures and studying the resulting spanwise screech

mode. The spanwise-oblique shock-cell structures were produced using

imperfectly expanded convergent–divergent rectangular nozzles

(aspect ratio = 5) with non-uniform exit geometries. Three geometries

were studied: (a) a nozzle with a spanwise uniform edge,

(b) a nozzle with a spanwise oblique (single-bevelled) edge,

and (c) a nozzle that had two spanwise oblique

(double-bevelled) cuts to form an arrowhead-shaped nozzle. For all

nozzles considered, the screech mode was antisymmetric in the

transverse (smaller nozzle dimension) direction allowing focus on

changes in the spanwise direction. Three types of spanwise modes were

observed: symmetric (I), antisymmetric (II), and oblique (III). The

following significant results emerged: (i) for all cases the screech

mode corresponds with the spanwise shock-cell structure, (ii) when

multiple screech modes are present, the technique presented here

makes it possible to distinguish between coexisting and mutually

exclusive modes, (iii) the strength of shocks 3 and 4 influences the

screech source amplitude and determines whether screech is unsteady.

The results presented here offer hope for a better understanding of

screech and for tailoring shock-containing jets to minimize fatigue

failure of aircraft components.
Mass transfer dominated by thermal diffusion in

laminar boundary layers
Authors: GARCÍA-YBARRA PEDRO L. , CASTILLO JOSE L.
Published: July 2002

The concentration distribution of massive dilute species (e.g.
aerosols,

heavy vapours,

etc.) carried in a gas stream in non-isothermal boundary layers is studied
in the

large-Schmidt-number limit, Sc[Gt ]1, including the cross-mass-transport

by thermal diffusion

(Ludwig–Soret effect). In self-similar laminar boundary layers, the
mass

fraction

distribution of the dilute species is governed by a second-order ordinary

differential

equation whose solution becomes a singular perturbation problem when

Sc[Gt ]1. Depending on the sign of the temperature gradient, the

solutions exhibit different

qualitative behaviour. First, when the thermal diffusion transport is directed
toward

the wall, the boundary layer can be divided into two separated regions:
an outer

region

characterized by the cooperation of advection and thermal diffusion and
an inner

region in the vicinity of the wall, where Brownian diffusion accommodates
the mass

fraction to the value required by the boundary condition at the wall. Secondly,
when

the thermal diffusion transport is directed away from the wall, thus competing

with the

advective transport, both effects balance each other at some intermediate
value

of the similarity variable and a thin intermediate diffusive layer separating

two outer regions

should be considered around this location. The character of the outer solutions

changes sharply across this thin layer, which corresponds to a second-order
regular

turning point of the differential mass transport equation. In the outer
zone from the

inner layer down to the wall, exponentially small terms must be considered
to account

for the diffusive leakage of the massive species. In the inner zone, the
equation

is solved in terms of the Whittaker function and the whole mass fraction

distribution is

determined by matching with the outer solutions. The distinguished limit
of Brownian

diffusion with a weak thermal diffusion is also analysed and shown to match
the two

cases mentioned above.
On the decay of Burgers turbulence
Authors: GURBATOV S. N. , SIMDYANKIN S. I. , AURELL E. , FRISCH U. , TÓTH G.
Published: July 2002

This work is devoted to the decay of random solutions of the unforced Burgers
equation in one dimension in the limit of vanishing viscosity.
The initial velocity is homogeneous and Gaussian with a spectrum proportional to
kn at small wavenumbers
k and falling off quickly at large wavenumbers.
Orthonormal wavelet decomposition of turbulent
flows: intermittency and coherent structures
Authors: CAMUSSI R. , GUJ G.
Published: July 2002

Experimental data obtained in various turbulent flows are
analysed by means of
orthogonal wavelet transforms. Several configurations are analysed: homogeneous
grid turbulence at low and very low Reλ,
and fully developed jet turbulence at moderate
and high Reλ. It is shown by means of the
wavelet decomposition in combination
with the form of scaling named extended self-similarity that some
statistical properties
of fully developed turbulence may be extended to low-Reλ
flows. Indeed, universal properties related to intermittency are
observed down to Reλ≃10.
Furthermore, the
use of a new conditional averaging technique of velocity signals, based
on the wavelet
transform, permits the identification of the time signatures of coherent
structures
which may or may not be responsible for intermittency depending on the
scale of
the structure itself. It is shown that in grid turbulence,
intermittency at the smallest
scales is related to structures with small characteristic size and with
a shape that may
be related to the passage of vortex tubes. In jet turbulence, the
longitudinal velocity
component reveals that intermittency may be induced by structures with
a size of
the order of the integral length. This effect is interpreted as
the signature of the
characteristic jet mixing layer structures. The structures identified
on the transverse
velocity component of the jet case turn out on the other hand not to be
affected by
the mixing layer and the corresponding shape is again correlated with the
signature
of vortex tubes.
Numerical computation of capillary–gravity

interfacial solitary waves
Authors: LAGET O. , DIAS F.
Published: July 2002

Two types of capillary–gravity interfacial solitary waves

are computed numerically:

‘classical’ solitary waves which bifurcate from a

uniform flow at a critical value of the

velocity and solitary waves in the form of wave packets which bifurcate

from a train of

infinitesimal periodic waves with equal phase and group velocities. The

effects of finite amplitude are shown to be quite different from the pure
gravity

case for the classical

solitary waves. The solitary waves in the form of wave packets, which are
known

to exist for small density ratios, are shown to exist even for larger density
ratios,

but only at finite amplitude. The numerical code is based on an integro-differential

formulation of the full Euler equations. The experimental results of Koop

& Butler

(1981), which have been compared earlier with results from model equations,
are

compared with the present numerical results.
Coupling of twin rectangular supersonic jets
Authors: RAMAN GANESH , TAGHAVI RAY
Published: July 2002

Twin jet plumes on aircraft can couple, producing dynamic

pressures significant

enough to cause structural fatigue. For closely spaced jets with

a moderate aspect

ratio (e.g. 5), previous work has established that two coupling

modes (antisymmetric

and symmetric) are kinematically permissible. However, the

dynamics of twin-jet coupling have remained unexplored. In this

paper a more fundamental assessment of the

steady and unsteady aspects of twin-jet coupling is attempted.

While we document

and discuss the nozzle spacings and Mach numbers over which

phase-locked coupling occurs, our concentration is much more on

answering the following questions:

(a) What mechanism causes the jets to couple in

one mode or the other? (b) Why do

the jets switch from one mode to another? (c) Are the

two modes mutually exclusive

or do they overlap at the transition point? Our results reveal,

among many things,

the following. (i) For very closely spaced twin jets in the

side-by-side configuration

phased feedback based on source to nozzle exit distance of adjacent

jets does not

fully explain the coupling modes. However, the ‘null’

phase regions surrounding the

jets where the phase of an acoustic wavefront (arriving from

downstream) does not

vary appears to correlate well with the existence of the symmetric

mode. When the ‘null’ regions of adjacent jets do not overlap

antisymmetric coupling occurs and when

they do overlap the jets couple symmetrically. We provide a simple

correlation using a parameter (α) that can be used as a simple test
to

determine the mode of coupling.

(ii) The switch from the antisymmetric to the symmetric mode of

coupling appears to occur because of an abrupt shift in the effective

screech source from the third to

the fourth shock, which in turn causes the ‘null’

phase region surrounding the jets to

grow abruptly and overlap. (iii) The two modes are mutually

exclusive. Our results

provide considerable insight into the twin-jet coupling problem and

offer hope for

designing twin-jet configurations that minimize damage to aircraft

components.
From quasi-geostrophic to strongly nonlinear

monopolar vortices in a paraboloidal

shallow-water-layer experiment
Authors: STEGNER A. , ZEITLIN V.
Published: July 2002

We perform a detailed experimental study of

large-scale vortices propagating in the

rotating shallow-water layer in a paraboloidal vessel. A

specific data acquisition

technique is used in order to ensure precise measurements of

the free-surface elevation.

We find two qualitatively different types of vortex behaviour

controlled by the relative

elevation value. For small elevations we observe a standard

quasi-geostrophic pattern

with an asymmetric secondary circulation around an initially

symmetric vortex which

leads to a meridional drift and Rossby wave radiation. This

type of behaviour is

exhibited by both cyclonic and anticyclonic vortices. For

relative elevations larger than 1 (nonlinear regime) the

necessarily anticyclonic vortices are drifting strictly zonally

maintaining their circular symmetry during the viscous decay.

By varying the initial

latitude of the vortex we were able to check that in the

nonlinear regime the vortex

lifetime is not sensitive to the beta-effect, while it is

the case in the quasi-geostrophic

regime. In the same way we show that the observed difference

in cyclone–anticyclone

lifetimes is not influenced by the beta-effect.
Dynamics of radiating cold domes on a sloping bottom
Authors: SWATERS GORDON E.
Published: July 2002

Numerical simulations of benthic gravity-driven currents along
continental shelves
suggest they exhibit considerable time and spatial variability and tend
to organize
themselves into large-scale bottom-intensified cold domes or eddies. Attempts
to
derive simple relations governing the evolution of the spatial moments
of the mass
equation for baroclinic eddies have failed because it is not clear how
to express the
form or wave drag stresses associated with the excited (topographic) Rossby
wave field
in the surrounding fluid in terms of the eddy moments. We develop a simple
model for
the leading-order time evolution of a cold dome configuration which initially
nearly
satisfies the Mory–Stern isolation constraint. As the topographic
Rossby wave field in
the surrounding fluid interacts with the cold dome, higher azimuthal modes
are excited
within the cold dome which develop into spiral-like filamentary structures
on the eddy
boundary. The trajectory followed by the position of the maximum height
of the cold
dome corresponds to sub-inertial along- and cross-slope oscillations superimposed
on
a mean along-slope drift (well described by the Nof velocity). Nevertheless,
the theory
suggests that there are no oscillations (at least to second order) in the
horizontal
spatial moments of the eddy height, that is, the centre of mass of the
eddy moves
steadily in the along- and down-slope directions (i.e. ‘southwestward’

relative to the topographic β-plane). The theoretical analysis
is in good agreement with a nonlinear numerical simulation which we present.
Unsteady separation past moving surfaces
Authors: DEGANI A. T. , WALKER J. D. A. , SMITH F. T.
Published: July 2002

Unsteady boundary-layer development over moving walls in the limit
of infinite
Reynolds number is investigated using both the Eulerian and Lagrangian
formulations.
To illustrate general trends, two model problems are considered, namely
the
translating and rotating circular cylinder and a vortex convected in a
uniform flow
above an infinite flat plate. To enhance computational speed and accuracy
for the
Lagrangian formulation, a remeshing algorithm is developed. The calculated
results
show that unsteady separation is delayed with increasing wall speed and
is eventually
suppressed when the speed of the separation singularity approaches that
of the local
mainstream velocity. This suppression is also described analytically. Only

‘upstream-slipping’ separation is found to occur in the
model problems. The changes in the
topological features of the flow just prior to the separation that occur
with increasing
wall speed are discussed.
Collisional sheet flows of sediment driven by a turbulent fluid
Authors: JENKINS JAMES T. , HANES DANIEL M.
Published: July 2002

We consider a sheet flow in which heavy grains near a packed bed
interact with a
unidirectional turbulent shear flow of a fluid. We focus on sheet flows
in which the
particles are supported by their collisional interactions rather than by
the velocity
fluctuations of the turbulent fluid and introduce what we believe to be
the simplest
theory for the collisional regime that captures its essential features.

We employ a relatively simple model of the turbulent shearing of the
fluid and use
kinetic theory for the collisional grain flow to predict profiles of the
mean fluid velocity,
the mean particle velocity, the particle concentration, and the strength
of the particle
velocity fluctuations within the sheet. These profiles are obtained as
solutions to the
equations of balance of fluid and particle momentum and particle fluctuation
energy
over a range of Shields parameters between 0.5 and 2.5. We compare the
predicted
thickness of the concentrated region and the predicted features of the
profile of the
mean fluid velocity with those measured by Sumer et al. (1996).
In addition, we
calculate the volume flux of particles in the sheet as a function of Shields
parameter.

Finally, we apply the theory to sand grains in air for the conditions
of a sandstorm
and calculate profiles of particle concentration, velocity, and local volume
flux.
Direct numerical simulation of turbulence
modulation by particles in isotropic turbulence
Authors: BOIVIN MARC , SIMONIN OLIVIER , SQUIRES KYLE D.
Published: July 2002

The modulation of isotropic turbulence by particles has been investigated
using direct
numerical simulation (DNS). The particular focus of the present work is
on the class
of dilute flows in which particle volume fractions and inter-particle collisions
are
negligible. Gravitational settling is also neglected and particle motion
is assumed to
be governed by drag with particle relaxation times ranging from the Kolmogorov

scale to the Eulerian time scale of the turbulence and particle mass loadings
up to 1.
The velocity field was made statistically stationary by forcing the low
wavenumbers
of the flow. The calculations were performed using 963 collocation
points and the
Taylor-scale Reynolds number for the stationary flow was 62. The effect
of particles
on the turbulence was included in the Navier–Stokes equations using
the point-force
approximation in which 963 particles were used in the calculations.
DNS results
show that particles increasingly dissipate fluid kinetic energy with increased
loading,
with the reduction in kinetic energy being relatively independent of the
particle
relaxation time. Viscous dissipation in the fluid decreases with increased
loading
and is larger for particles with smaller relaxation times. Fluid energy
spectra show
that there is a non-uniform distortion of the turbulence with a relative
increase in
small-scale energy. The non-uniform distortion significantly affects the
transport of
the dissipation rate, with the production and destruction of dissipation
exhibiting
completely different behaviours. The spectrum of the fluid–particle
energy exchange
rate shows that the fluid drags particles at low wavenumbers while the
converse is true
at high wavenumbers for small particles. A spectral analysis shows that
the increase
of the high-wavenumber portion of the fluid energy spectrum can be attributed
to
transfer of the fluid–particle covariance by the fluid turbulence.
This in turn explains
the relative increase of small-scale energy caused by small particles observed
in the
present simulations as well as those of Squires & Eaton (1990) and
Elghobashi &
Truesdell (1993).
Large-eddy simulation of flow over wavy surfaces
Authors: HENN DOUGLAS S. , SYKES R. IAN
Published: July 2002

Large-eddy simulation is used to investigate fully developed turbulent
flow in a neutral
channel wherein the lower wall is sinusoidal. The numerical results are
compared with
experimental observations for wave slopes ranging from 0 to 0.628. Particular
emphasis
is placed on the separated flow induced by a large-amplitude wave. A detailed

comparison with the data of Buckles, Hanratty & Adrian (1984) shows
generally
good agreement. Large-eddy simulation surface pressures are integrated
to calculate
form drag as a function of wave slope. Drag is found to increase quadratically

with slope for small-amplitude waves, with a somewhat slower increase for
larger
amplitudes. However, comparison with experimental measurements is confounded

by uncertainties with the values reported in the literature. An interesting
feature
characteristic of all wavy-surface simulations is an increase in transverse
velocity
fluctuations on the wave upslope. Although the precise mechanism responsible
is
not known, analysis shows it to be associated with temporally persistent
vortex-like
structures localized near the surface. The magnitude of the fluctuation
increase
appears to scale quadratically with slope for small-amplitude waves, in
contrast to
the streamwise fluctuations, which increase linearly.
Plugging by hydrodynamic bridging during flow

of stable colloidal particles within

cylindrical pores
Authors: RAMACHANDRAN VENKATACHALAM , FOGLER H. SCOTT
Published: July 2002

This paper describes the flow-induced retention of charge stabilized colloidal particles

during flow through cylindrical pores. Current models describing the low-Reynolds-number flow behaviour of particulate suspensions through porous media do not

predict retention of stable colloidal particles if the particles are smaller in size than

the pores, and the particles and the pores have like surface charges. Retention is not

expected under these conditions because the small particle size relative to the pore

constriction size precludes straining (physical capture of particles larger than the pore

constriction) while particle–pore surface electrostatic repulsion prevents deposition.

However, the experiments show that substantial particle retention can occur under

these conditions. The mechanism causing particle retention under these conditions,

hydrodynamic bridging, is flow-induced. In this mechanism, hydrodynamic forces

acting on particles arriving at a pore entrance do not allow their simultaneous

passage through the pore, resulting in the formation of a particle bridge across the

pore constriction. This paper reports experiments elucidating the effects of velocity,

particle concentration, and the ratio of pore size to particle size on retention by

hydrodynamic bridging. For flow through cylindrical pores, the effect of velocity on

retention by bridging is opposite to that of retention by deposition. Furthermore,

observations indicate the existence of a critical flow velocity necessary for particle

bridging to occur. This critical velocity is a measure of the net colloidal interparticle

and particle–porous medium repulsion that must be overcome by the hydrodynamic

forces for bridging to occur. Approximate theoretical calculations of the trajectories

of two particles approaching an isolated cylindrical pore are also presented. These

calculations show that bridging is indeed possible in the Stokes flow regime for the

experimental conditions considered.
The turbulent burning velocity for large-scale and small-scale turbulence
Authors: PETERS N.
Published: July 2002

The level-set approach is applied to a regime of premixed turbulent
combustion where
the Kolmogorov scale is smaller than the flame thickness. This regime is
called the
thin reaction zones regime. It is characterized by the condition that small
eddies can
penetrate into the preheat zone, but not into the reaction zone.

By considering the iso-scalar surface of the deficient-species mass
fraction Y
immediately ahead of the reaction zone a field equation for the scalar
quantity
G(x, t)
is derived, which describes the location of the thin reaction zone. It
resembles the level-set equation used in the corrugated flamelet regime, but the resulting
propagation
velocity s*L normal to the front
is a fluctuating quantity and the curvature term
is multiplied by the diffusivity of the deficient species rather than
the Markstein
diffusivity. It is shown that in the thin reaction zones regime diffusive
effects are
dominant and the contribution of s*L to

the solution of the level-set equation is small.

In order to model turbulent premixed combustion an equation is used
that contains
only the leading-order terms of both regimes, the previously analysed corrugated

flamelets regime and the thin reaction zones regime. That equation accounts
for
non-constant density but not for gas expansion effects within the flame
front which
are important in the corrugated flamelets regime. By splitting G
into a mean and a
fluctuation, equations for the Favre mean [Gtilde]and the variance

[Gtilde]″2 are derived. These
quantities describe the mean flame position and the turbulent flame brush
thickness,
respectively. The equation for [Gtilde]″2 is
closed by considering two-point statistics. Scaling
arguments are then used to derive a model equation for the flame surface
area ratio
[rhotilde]. The balance between production, kinematic restoration and
dissipation in this
equation leads to a quadratic equation for the turbulent burning velocity.
Its solution
shows the ‘bending’ behaviour of the turbulent to laminar burning
velocity ratio
sT/sL,
plotted as a function of v′/sL.

It is shown that the bending results from the
transition from the corrugated amelets to the thin reaction zones regimes.
This is
equivalent to a transition from Damköhler's large-scale to his
small-scale turbulence
regime.
Spin-up in a tank induced by a rotating bluff body
Authors: MAYNES D. , KLEWICKI J. , McMURTRY P.
Published: July 2002

Spin-up of a turbulent flow in a cylindrical tank caused by a rotating bluff body has
been investigated using flow visualization, fluid velocity measurements, and hydrodynamic
torque measurements. During the spin-up process three distinct temporal
regimes exist. These regimes are: (i) a build-up regime where the torque and the
tangential velocity fluctuations in the close proximity of the body remain constant; (ii) a
decay regime where these quantities decay with power-law relations; and (iii) a mean
flow steady state where these values remain relatively constant. Experiments were
conducted in two tanks differing in volume by a factor of 80 and with a large range
of bluff body sizes. A non-dimensional time scale, τ, based upon turbulent diffusion
is determined and the tangential velocity fluctuations and torque coefficient start to
decay at a fixed value of τ. Likewise, steady state is attained at a larger fixed value
of τ. This time scaling is physically based upon the time required for momentum to
be transferred over the entire tank volume due to turbulent diffusion, and is general
for any body size, tank size, rotation rate, and acceleration rate.
Experimental investigation of the global instability of plane sheet flows
Authors: de LUCA LUIGI
Published: July 2002

A global stability investigation of two-dimensional vertical liquid sheet flows is experimentally
carried out. The motivation is that previous investigations addressed the
study of the local absolute/convective character of such flows, thus they are not able
to predict the actual critical flow Weber number corresponding to sheet rupture. The
objective of the paper is twofold: first, the link between local absolute and global
instabilities is investigated and the measured length of the absolute instability region
is correlated with the non-parallelism parameter (sheet slenderness ratio which is the
reciprocal of the Froude number); then, a criterion to predict the flow Weber number
value at sheet rupture is given for which the critical Weber number is correlated with
Froude and Reynolds numbers. Tests are carried out on liquid (low-concentration
water solutions of surfactants and low-viscosity motor oil) sheets issuing from a nozzle
with a long horizontal exit section in still air under the gravitational field. A major
goal of the experiments is the determination of the vertical location where the local
Weber number equals unity, because this yields the length of the absolute instability
region. This location is determined by observing the standing sinuous waves generated
by an obstacle placed normally to the sheet, and by measuring the angle between the
tangent to the wave at the obstacle and the vertical direction for the minimum liquid
flow rate necessary to maintain the sheet stable (global instability onset).
Numerical simulation of crossing-shock-wave/turbulent-boundary-layer
interaction using a two-equation model of turbulence
Authors: KNIGHT D. , GNEDIN M. , BECHT R. , ZHELTOVODOV A.
Published: July 2002

A crossing-shock-wave/turbulent-boundary-layer interaction is investigated using the
k–ε turbulence model with a new low-Reynolds-number model based on the approach
of Saffman (1970) and Speziale et al. (1990). The crossing shocks are generated by
two wedge-shaped fins with wedge angles α1 and α2 attached normal to a flat
plate on which an equilibrium supersonic turbulent boundary layer has developed.
Two configurations, corresponding to the experiments of Zheltovodov et al. (1994,
1998a, b), are considered. The free-stream Mach number is 3.9, and the fin angles
are (α1, α2) = (7°, 7°) and (7°, 11°). The computed surface pressure displays very
good agreement with experiment. The computed surface skin friction lines are in
close agreement with experiment for the initial separation, and are in qualitative
agreement within the crossing shock interaction region. The computed heat transfer
is in good agreement with experiment for the (α1, α2) = (7°, 7°) configuration. For
the (α1, α2) = (7°, 11°) configuration, the heat transfer is significantly overpredicted
within the three-dimensional interaction. The adiabatic wall temperature is accurately
predicted for both configurations.
Some observations on the typology of linguistic theories
Authors: ACKERMAN FARRELL
Published: July 2002

Gilles Fauconnier & Eve Sweetser (eds.),Space, worlds, and grammar.
Chicago & London: University of Chicago Press, 1996. 355 Pp.

Masayoshi Shibatani & Sandra Thompson (eds.),Grammatical constructions:
their form and meaning. Oxford: Clarendon Press, 1996. Pp. xvii+345.

Several years ago a volume of articles appeared called The view from Building
20 (Hale & Keyser 1993). As suggested by the title, the contributions
reflected trends guiding the theoretical paradigm pre-eminently associated
with MIT. After reading this collection, a colleague quipped that she
wondered how well the view from Building 20 accorded with the broad
research world beyond it. In this connection, the two books under review
represent perspectives on language analysis which encourage one to pause
and consider the present theoretical landscape in linguistics, and, less
directly, the role of linguistics within modern cognitive science. Among their
other merits, both books provide a rich and useful illustration of some of the
perspectives on language analysis outside of Building 20. In doing so, they
also help to define a more interesting research landscape than that usually
characterized as an opposition between ‘formalists’ versus ‘cognitive/functionalists’.
Telling general linguists about Altaic
Authors: GEORG STEFAN , MICHALOVE PETER A. , RAMER ALEXIS MANASTER , SIDWELL PAUL J.
Published: July 2002

The hypothesis of an Altaic language family, comprising the Turkic, Mongolic,
Tungusic, Korean and, in most recent versions, Japanese languages continues to be
a viable linguistic proposal, despite various published claims that it is no longer
accepted. A strong body of research continues to appear, developing and refining the
hypothesis, along with publications that argue against a demonstrated relationship
among these languages. This paper shows that many of the arguments against a
genetic relationship fail to address the criteria demanded in modern historical
linguistics, while many of the responses from proponents of the Altaic theory have
failed to address the criticisms raised. We hope that arguments focusing on the real
issues of phonological correspondences and morphological systems will shed greater
light on the relationship among these languages.
Phatic interpretations and phatic communication
Authors: ŽEGARAC VLAD , CLARK BILLY
Published: July 2002

This paper considers how the notion of phatic communication can best be understood
within the framework of Relevance Theory. To a large extent, we are exploring a
terminological question: which things which occur during acts of verbal communication
should the term ‘phatic’ apply to? The term is perhaps most frequently
used in the phrase ‘phatic communication’, which has been thought of as an
essentially social phenomenon and therefore beyond the scope of cognitive pragmatic
theories. We suggest, instead, that the term should be applied to interpretations and
that an adequate account of phatic interpretations requires an account of the
cognitive processes involved in deriving them. Relevance Theory provides the basis
for such an account. In section 1, we indicate the range of phenomena to be explored.
In section 2, we outline the parts of Relevance Theory which are used in our account.
In section 3, we argue that the term ‘phatic’ should be
applied to interpretations, and
we explore predictions about phatic interpretations which follow from the framework
of Relevance Theory, including the claim that phatic interpretations should be
derived only when non-phatic interpretations are not consistent with the Principle of
Relevance. In section 4 we consider cases where cognitive effects similar to those
caused by phatic interpretations are conveyed but not ostensively communicated.
Final complementizers in hybrid languages
Authors: BAYER JOSEF
Published: July 2002

Recent developments in syntactic theory suggest that phrase structure is cross-linguistically more uniform than assumed so far, and that the order spec-head-complement may be the only permissible one. The present article takes issue with this
view, showing that the derivation of final complementizers from initial ones by means
of IP-raising faces serious difficulties. The discussion focuses on Bengali and similar
languages which may be called ‘hybrid’ because both orders, IP-C as well as C-IP,
are attested. Five arguments are raised which indicate that these orders are not
derivationally connected. The discussion bears results which may also be of interest
for linguistic typology, language change and acquisition.
Against featural alignment
Authors: PIGGOTT GLYNE L.
Published: July 2002

Morphemes are sometimes expressed by elements that are less than full segments,
and, in a given language, the position of these elements in a word may vary. A recent
analysis of these ‘mobile morphemes’ claims that their distribution is best explained
in an optimality-theoretic framework that incorporates a set of featural alignment
constraints (Akinlabi 1996). This paper argues that featural alignment plays no role
in the realization of ‘mobile morphemes’. Instead, it recognizes a set of licensing
constraints that explicitly identifies where featural exponents of such morphemes may
appear in a word. Crucially, these licensing constraints, unlike featural alignment, are
not morpheme-specific and therefore enjoy cross-linguistic support. Analyses of
Chaha labialization, Terena nasalization, High tone realization in the Edoid
associative construction and Southern Sami vowel lowering in terms of licensing are
shown to be superior to the alignment-theoretic ones on both descriptive and
explanatory grounds.
Staged pinch for controlled thermonuclear fusion
Authors: RAHMAN H. U. , NEY P. , WESSEL F. J. , ROSTOKER N.
Published: July 2002

Staged pinch implosions provide a means to couple energy to a small-diameter
fibre on an extremely fast time scale, circumventing the limitations of
conventional pinches. In this scheme the generator current initially traverses
an
intermediate hollow plasma shell, which compresses onto the fibre placed
coaxially and transfers the current to the fibre with a significantly reduced
risetime. The results are impressive, since the delivered peak power is
increased
by several orders of magnitude, the coupling efficiency improves, and the
most
dangerous plasma instabilities that commonly plague high-density/high-temperature
pinches are eliminated. This technique can be fielded on both fast
and slow generators (i.e. tens of nanoseconds to microseconds), making
it
feasible to extend the concept to a wide range of presently assembled systems.
Staging may therefore present a dramatically new means of pulsed-energy
conversion, which could find many applications. In addressing the requirements
for thermonuclear fusion in a staged Z pinch, our preliminary
calculations
based on zero-D models suggest the potential for a significant
thermonuclear
burn with generator currents of the order of a few megaamperes and one
microsecond risetime. Studies are actively underway at various places around
the world (England, France, Germany and Russia) as well as in the USA
(UCI/UCR) to investigate different aspects of staged pinching and its
applications, particularly those leading to controlled thermonuclear fusion.
Expansions of the mildly relativistic dispersion
function for nearly perpendicular electron
cyclotron ray tracing
Authors: SHKAROFSKY I. P.
Published: July 2002

To trace rays very close to the nth electron cyclotron
harmonic, we need the
mildly relativistic plasma dispersion function and its higher-order derivatives.

Expressions for these functions have been obtained as an expansion for
nearly
perpendicular propagation in a region where computer programs have
previously experienced difficulty in accuracy, namely when the magnitude
of
(c/vt)2
(ω−nωc)/ω
is between 1 and 10. In this region, the large-argument
expansions are not yet valid, but partial cancellations of terms occur.
The
expansion is expressed as a sum over derivatives of the ordinary dispersion

function Z. New expressions are derived to relate higher-order
derivatives of Z
to Z itself in this region of concern in terms of a finite series.
Turn transition, creak and glottal stop in Finnish talk-in-interaction
Authors: Ogden Richard
Published: July 2002

Finnish talk-in-interaction is shown to use creak and glottal stops distinctively. Creak has turn-yielding functions, and glottal stops have turn-holding functions. Rather than either intuition or the use of large corpora with no attention to the interactional function in which the talk is embedded, the methodology used is that of interactional linguistics (e.g. Couper-Kuhlen & Selting 1996 for a prosodic approach), which places emphasis on demonstrating participants' local orientation to linguistic categories within interactional sequences.
Temporal variability of viruses, bacteria, phytoplankton and zooplankton in the western English Channel off Plymouth
Authors: Rodríguez F. , Fernández E. , Head R.N. , Harbour D.S. , Bratbak G. , Heldal M. , Harris R.P.
Published: July 2002

The temporal distribution of autotrophic and heterotrophic components of the planktonic community was studied from samples collected weekly at station L4, located to the south of Plymouth, UK, from October 1992 to January 1994. Phytoplankton succession followed the typical pattern of temperate waters, the development of a summer Gyrodinium aureolumbloom being the most prominent feature. Bacterial numbers were significantly correlated with temperature during autumn and winter, whereas resource availability and predation, including viruses, appear to be the most important controlling factors in spring and summer. High mesozooplankton densities, mainly copepods, were observed throughout most of the study associated with a series of diatom blooms, and also during autumn when low phytoplankton biomass was measured. This data set was analysed in order to build up conceptual trophodynamic models whereby the role of biological communities on the cycling of organic matter could be inferred. The results obtained in this study provide empirical evidence supporting the existence of a sucession of trophic organization patterns in a coastal temperate environment. Classical models (herbivorous or microbial webs) appeared episodically whereas transition models (multivorous web) dominated throughout most of the seasonal cycle.
Epilithic boulder communities of Lough Hyne, Ireland: the influences of water movement and sediment
Authors: Maughan Ben C. , Barnes David K.A.
Published: July 2002

The Marine Nature Reserve of Lough Hyne (south-west Ireland) encompasses an extremely wide range of marine conditions within a small area. A total of 378 boulders were collected from a range of depths at five sites subjected to very different degrees of water movement and sedimentation. Encrusting biota were identified and the communities compared between sites and upper and lower surfaces. In all, 114 taxa were identified. Alpha diversity was generally found to be higher for lower surfaces at sites with intermediate flow/disturbance. Sites with high water flow had much greater space occupation, predominantly cheilostomatid bryozoans. Multivariate analyses divided the samples into six groupings. Similarity percentage analysis (SIMPER) was used to indicate particular species characteristic of each group. Equations for the species-area curves generated tended to indicate communities at equilibrium except at sites subjected to stresses such as high sediment load or high disturbance. For high disturbance sites it was apparent that number of species cm−2 was significantly negatively correlated with surface area of rock implying non-random distribution.
Two new species of Monstrilla (Copepoda: Monstrilloida) from Brazil
Authors: Suárez-Morales E. , Dias C.
Published: July 2002

Several specimens of monstrilloid copepods were collected in different localities of Brazil between 1993 and 1997. The taxonomic analysis of these specimens yielded the identification of two new species of Monstrilla. The first one, M. careli sp. nov. can be distinguished by a combination of several characters, including its body proportions, with a very long cephalothorax, by the particularly long terminal segment of the antennules, by the structure of its fifth legs, and by the very long dorsal seta on the caudal rami. The second species, M. brasiliensis sp. nov. can be distinguished by the peculiar features of its fifth leg, with a patch of long and stout hair-like setae along its outer margin; it has also a notched protuberance near the antennule bases. It has a notch on the anterior protuberance of the genital somite, and a ventrally swollen cephalothorax. This species, together with M. inserta Scott bears a pair of enigmatic structures which are either modified sensillae or a vestigial postantennular appendage not previously described in the Monstrilloida.
A new species of the genus Celleporella (Bryozoa: Cheilostomatida) from the European Atlantic Coast
Authors: César-Aldariz J. , Fernández-Pulpeiro E. , Reverter-Gil O.
Published: July 2002

A new species of the genus Celleporella (Celleporella galaica sp. nov.) is described from material collected in Galicia (north-west Spain).
A History of Forestry in Sarawak
Authors: KAUR AMARJIT
Published: July 2002

Tropical deforestation and the associated economic, ecological, and equity issues have become a matter of general interest and concern for scholars, international conservation and environmental organizations, and local pressure groups. ‘Remote’ outposts like Sarawak (‘Land of the White Rajahs’) have suddenly been thrust into the limelight as conflicts arose between different interest and ethnic groups for allocation of land and rights to utilize forest resources. A review of existing knowledge and data is therefore necessary to set rainforest clearance in Sarawak in a local, national, and international political economy context. This paper looks at the following themes: the historical legacy of ‘commercial’ extraction of forest products; the growth of the timber sector and the development of state forest regulation; and the conflicts of interest for allocation of land and rights to utilize forest resources.
Silencing the Voice of Agricultural Labourers in South Gujarat
Authors: Breman Jan
Published: July 2002

. . . according to Manu, for slandering a Vaisya or a Shudra the fines are only twenty-five or twelve panas, respectively. For members of the lower orders who slander their betters the penalties are much more severe . . . the equality of the law was never admitted in ancient India, and was quite contrary to most Indian thought. (A. L. Basham, The Wonder That Was India, 1954: 120).
Indian Merchant Networks Outside India in the Nineteenth and Twentieth Centuries: A Preliminary Survey
Authors: Markovits Claude
Published: July 2002

In spite of the recent flowering of studies on the South Asian diaspora, we are nevertheless left with many gaps in our knowledge and many unanswered questions. The bulk of existing work is still focused on the migration of agricultural labour and the ‘Little Indias’ it spawned in various corners of the world. The recent migrations of educated professionals to the countries of the ‘First World’, particularly the USA, are also attracting increasing attention. The whole field of migration and diaspora studies remains, however, dominated by a host country perspective which tends to obliterate the general picture from the point of view of South Asian history.
THE MEANING OF ΠPOEΓPAΦH IN THE CONTEXT OF GALATIANS 3.1
Authors: DAVIS BASIL S.
Published: July 2002

When Paul uses the verb πρoεγραϕη in Gal 3.1 he is not referring to an earlier writing of his, nor is he appealing to prophecies written in scripture. It may be possible to see here an allusive employment of mystery vocabulary. The dominant view is that πρoγραϕη implies a purely verbal depiction of Christ, the visual language being understood metaphorically. This article argues that the visual aspect of πρoγραϕη signifies Paul's display of the crucified Christ who was living in him according to the immediately preceding verses 2.19–21. Paul displayed the crucified Christ primarily in persecution suffered for his gospel.