共查询到20条相似文献,搜索用时 15 毫秒
1.
Results of numerical simulations of a quasi-one-dimensional unsteady flow in a channel considered as an element of an air-breathing
engine are presented. The influence of parameters of energy supplied in the pulsed-periodic mode (power, pulse frequency,
and distribution of energy sources along the channel) on the characteristics of the flow with Mach numbers M
0 = 2.4–4.0 at the channel entrance is determined. A channel configuration that allows the energy supply distribution to be found from
the condition of restriction of the maximum value of the gas temperature is proposed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 3–11, January–February, 2009. 相似文献
2.
Christophe Brun Margareta Petrovan Boiarciuc Marie Haberkorn Pierre Comte 《Theoretical and Computational Fluid Dynamics》2008,22(3-4):189-212
Astract The present study is a contribution to the analysis of wall-bounded compressible flows, including a special focus on wall
modeling for compressible turbulent boundary layer in a plane channel. large eddy simulation (LES) of fully developed isothermal
channel flows at Re = 3,000 and Re = 4,880 with a sufficient mesh refinement at the wall are carried out in the Mach number range 0.3 ≤ M ≤ 3 for two different source term formulations: first the classical extension of the incompressible configuration by Coleman
et al. (J. Fluid Mech. 305:159–183, 1995), second a formulation presently derived to model both streamwise pressure drop and
streamwise internal energy loss in a spatially developed compressible channel flow. It is shown that the second formulation
is consistent with the spatial problem and yields a much stronger cooling effect at the wall than the classical formulation.
Based on the present LES data bank, compressibility and low Reynolds number effects are analysed in terms of coherent structure
and statistics. A study of the universality of the structure of the turbulence in non-hypersonic compressible boundary layers
(M≤5) is performed in reference to Bradshaw (Annu. Rev. Fluid. Mech. 9:33–54, 1977). An improvement of the van Driest transformation
is proposed; it accounts for both density and viscosity changes in the wall layer. Consistently, a new integral wall scaling
(y
c+) which accounts for strong temperature gradients at the wall is developed for the present non-adiabatic compressible flow.
The modification of the strong Reynolds analogy proposed by Huang et al. (J. Fluid Mech. 305:185–218, 1995) to model the correlation
between velocity and temperature for non-adiabatic wall layers is assessed on the basis of a Crocco–Busemann relation specific
to channel flow. The key role of the mixing turbulent Prandtl number Pr
m
is pointed out. Results show very good agreement for both source formulations although each of them involve a very different
amount of energy transfer at the wall.
The present work was performed within the framework of the French–German research initiative “large eddy simulation of complex
flows’ (UR 507). The computing resources were provided by IDRIS-France. The authors gratefully acknowledge the financial support
from the Centre National de la Recherche Scientifique (CNRS), the Centre d’été Mathématique de Recherche Avancée en Calcul
Scientifique (CEMRACS) and the Direction Générale de l’Armement (DGA/D4S). 相似文献
3.
V. M. Bazovkin A. P. Kovchavtsev G. L. Kuryshev A. A. Maslov S. G. Mironov D. V. Khotyanovsky A. V. Tsarenko I. S. Tsyryulnikov 《Journal of Applied Mechanics and Technical Physics》2009,50(4):638-645
Coefficients of heat transfer to the surface in a laminar hypersonic flow (M
∞
= 21) over plane and axisymmetric models with a compression corner are presented. These coefficients are measured by an infrared
camera. The parameters varied in the experiments are the angle of the compression corner and the distance to the corner point.
Characteristics of the flow with and without separation in the corner configuration are obtained. The measured results are
compared with direct numerical simulations performed by solving the full unsteady Navier-Stokes equations. Experiments with
controlled streamwise structures inserted into the flow are described. A substantial increase in the maximum values of the
heat-transfer coefficient in the region of flow reattachment after developed laminar separation is demonstrated.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 4, pp. 112–120, July–August, 2009. 相似文献
4.
A. Günther D. V. Papavassiliou M. D. Warholic T. J. Hanratty 《Experiments in fluids》1998,25(5-6):503-511
A two-component laser Doppler velocimeter with high spatial and temporal resolution was used to obtain measurements for fully
developed turbulent flow of water through a channel with an aspect ratio of 12 : 1 at Re=5700 (based on the centerline velocity and the half-height of the channel). Statistical quantities that were determined are
the mean streamwise velocity, the root-mean-square of the fluctuations of the streamwise and the normal velocities, the Reynolds
shear stress and higher order moments. Turbulence production is calculated from these quantities. Turbulence statistics obtained
from experiments are compared with results from a direct numerical simulation at the same Reynolds number. The good agreement
validates a recent DNS, at Re=5700, which is approximately twice as large as used in most previous studies.
Received: 12 May 1997 / Accepted: 8 April 1998 相似文献
5.
S. V. Sukhinin S. P. Bardakhanov 《Journal of Applied Mechanics and Technical Physics》1998,39(2):220-227
The conditions of the onset of aeroacoustic resonance phenomena near a plate in a gas flow in a rectangular channel are studied
theoretically and experimentally in a two-dimensional formulation. The eigenfrequency as a function of the plate's chord and
its position in the channel, the shape of the eigenfunctions, and the effect of the Mach number of the basic gas flow versus
the eigenfrequencies and eigenfunctions and the mechanism of self-excited oscillations are determined. A mathematical model
by means of which the dependence of the resonance phenomena on the geometrical parameters of the structure were performed
is proposed and substantiated.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 2, pp. 69–77, March–April, 1998. 相似文献
6.
Reynolds-number-dependence of the maximum in the streamwise velocity fluctuations in wall turbulence
A survey is made of the standard deviation of the streamwise velocity fluctuations in near-wall turbulence and in particular
of the Reynolds-number-dependency of its peak value. The following canonical flow geometries are considered: an incompressible
turbulent boundary layer under zero pressure gradient, a fully developed two-dimensional channel and a cylindrical pipe flow.
Data were collected from 47 independent experimental and numerical studies, which cover a Reynolds number range of R
θ=U
∞
θ/v=300−20,920 for the boundary layer with θ the momentum thickness and R
+=u
*R/v=100-4,300 for the internal flows with R the pipe radius or the channel half-width. It is found that the peak value of the rms-value normalised by the friction velocity,
u
*, is within statistical errors independent of the Reynolds number. The most probable value for this parameter was found to
be 2.71±0.14 and 2.70±0.09 for the case of a boundary layer and an internal flow, respectively. The present survey also includes
some data of the streamwise velocity fluctuations measured over a riblet surface. We find no significant difference in magnitude
of the normalised peak value between the riblet and smooth surfaces and this property of the normalised peak value may for
instance be exploited to estimate the wall shear stress from the streamwise velocity fluctuations. We also consider the skewness
of the streamwise velocity fluctuations and find its value to be close to zero at the position where the variance has its
peak value. This is explained with help of the equations of the third-order moment of velocity fluctuations. These results
for the peak value of the rms of the streamwise velocity fluctuations and also the coincidence of this peak with the zero
value of the third moment can be interpreted as confirmation of local equilibrium in the near-wall layer, which is the basis
of inner-layer scaling. Furthermore, these results can be also used as a requirement which turbulence models for the second
and triple velocity correlations should satisfy.
The authors are indebted to Prof. P. Bradshaw for making available his list of references on this topic and for his remarks
on “active” and “inactive” motions. We also gratefully acknowledge discussions with Prof. I. Castro regarding the value of
σ
u
+
above rough walls. 相似文献
7.
V. P. Reutov A. B. Ezersky G. V. Rybushkina V. V. Chernov 《Journal of Applied Mechanics and Technical Physics》2007,48(4):469-478
Evolution of convective structures in a thin layer of an evaporating liquid (ethanol) located under a turbulent boundary layer
of an airflow is studied experimentally and theoretically. Evolution of the structures is examined under conditions of an
increased flow velocity. A transition is found from convective cells formed in the absence of the flow to convective rolls
elongated in the streamwise direction. The theoretical analysis is performed within a two-dimensional model of the flow in
the liquid layer. The boundary conditions on the liquid surface are obtained with the use of self-similar solutions for mean
fields in the airflow. The onset and evolution of a periodic system of rolls are simulated numerically. Theoretical conclusions
are compared with experimental data.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 3–14, July–August, 2007. 相似文献
8.
The stability of a laminar boundary layer flow under natural convection on a vertical isothermally heated wall is studied
analytically. The analysis is performed by using two different two-dimensional linear models: (1) The non-parallel flow model
in which the steady mean flow as well as the disturbance amplitude functions can change in the streamwise direction; (2) The
parallel flow model in which the effects of the mean flow and disturbance changes in the streamwise direction are neglected.
The linear non-parallel stability analysis is based on the so-called parabolised stability equations (PSEs) which have been
successfully applied to the stability analysis of forced convection boundary layers. In this study the PSE equations are applied
to natural convection boundary layers in order to show the difference between parallel and non-parallel stability analysis.
A second part of this study deals with the effects of variable properties, which are always present in natural convection
flows. They are analysed by an extended version of the Orr–Sommerfeld equation (EOSE).
Received on 31 May 2000 相似文献
9.
This work continues the studies of Khoo et al. (Exp. Fluids 29: 448–460, 2001), where experiments were performed in turbulent-channel
and flat-plate boundary-layer flows using near-wall hot-wire probes. The probability density function (pdf) of the wall-shear
stress and streamwise velocity fluctuations in the viscous sublayer, buffer region and beyond were compared and analyzed.
The convective velocity U
c of the streamwise velocity fluctuations in the very near-wall region was obtained using a two-point correlation technique.
It was found that in the viscous sublayer, U
c is approximately constant at 13u
τ
and 15u
τ
, respectively, for the channel and boundary-layer flows. Spectra data for the viscous sublayer are presented for the first
time, and the normalized spectral plots for different flow conditions collapse at high frequencies or wavenumbers, thus indicating
the possible presence of small-scale universality at different Reynolds numbers. The integral time scale corresponding to
the streamwise velocity fluctuations in the viscous sublayer is also presented.
Received: 18 October 2000/Accepted: 2 April 2001 相似文献
10.
Simultaneous velocity and concentration fields in a confined liquid-phase rectangular jet with a Reynolds number based on
the hydraulic diameter of 50,000 (or 10,000 based on the velocity difference between streams and the jet exit dimension) and
a Schmidt number of 1,250 were obtained by means of a combined particle image velocimetry (PIV) and planar laser-induced fluorescence
(PLIF) system. Data were collected at the jet exit and six further downstream locations. The velocity and concentration field
data were analyzed for flow statistics such as turbulent fluxes, turbulent viscosity and diffusivity, and turbulent Schmidt
number (Sc
T
). The streamwise turbulent flux was found to be larger than the transverse turbulent flux, and the mean concentration gradient
was not aligned with the turbulent flux vector. The average Sc
T
was found to vary both in streamwise and in cross stream directions and had a mean value around 0.8, a value consistent with
the literature. Spatial correlation fields of turbulent fluxes and concentration were then determined. The R
u′ϕ′ correlation was elliptical in shape with a major axis tilted downward with respect to the streamwise axis, whereas the R
v′ϕ′ correlation was an ellipse with a major axis aligned with the cross-stream direction. Negative regions of R
u′ϕ′ were observed in the outer streams, and these negatively correlated regions decayed with downstream distance and finally
disappeared altogether. The R
ϕ′ϕ′ correlation field was found to be an ellipse with the major axis inclined at about 45° with respect to the streamwise direction.
Linear stochastic estimation was used to interpret spatial correlation data and to determine conditional flow structures.
It is believed that a vortex street formed near the splitter plate is responsible for the negatively correlated region observed
in the R
u′ϕ′ spatial correlations of turbulent fluxes. A positive concentration fluctuation event was observed to correspond to a finger
of nearly uniform concentration fluid reaching out into the outer stream, whereas a negative event corresponds to a pocket
of nearly uniform fluid being entrained from the outer stream into the center jet region. Large-scale vortical structures
were observed in the conditional velocity fields with an elliptical shape and a streamwise major axis. The growth of the structure
size increased linearly initially but then grew more slowly as the flow transitioned toward channel flow.
Support of this work was provided by the National Science Foundation through grants CTS-9985678 and CTS-0336435 and by the
Dow Chemical Company. The author greatly acknowledge Charles Lipp at Dow Chemical and Ken Junk at Emerson Fisher for their
valuable assistance in the design and construction of the flow system. 相似文献
11.
Fluid flow at the interface of a porous medium and an open channel is the governing phenomenon in a number of processes of
industrial importance. Traditionally, this has been modeled by applying the Brinkman’s modification of Darcy’s law to obtain
the velocity profile in terms of an additional parameter known as the “apparent viscosity” or the “slip coefficient”. To test
this ad hoc approach, a detailed experimental investigation of the flow was conducted using Laser Doppler Anemometry (LDA) in the close
vicinity of the permeable boundary of a porous medium. The porous medium used in the experiments consisted of a network of
continuous glass strands woven together in a random fashion.
A Hele–Shaw cell was partially filled with a fibrous preform such that an open channel flow is coupled with the Darcy flow
inside the preform through the permeable interface of the preform. The open channel portion of the Hele–Shaw cell also acts
as an ideal porous medium of known in-plane permeability which is much higher than the permeability of the fibrous porous
medium. A viscous fluid is injected at a constant flow rate through the above arrangement and a saturated and steady flow
is established through the cell. Using LDA, steady state velocity profiles are accurately measured by traversing across the
cell in the direction perpendicular to the flow. A series of experiments were conducted in which fluid viscosity, flow rate,
solid volume fraction of the porous medium and depth of the Hele–Shaw cell were varied. For each and every case in which the
conditions for Hele–Shaw approximation were valid, the depth of the boundary layer zone or the screening length inside the
fibrous preform was found to be of the order of the channel depth. This is much larger as compared to the Brinkman’s prediction
of the screening length which is of the order of √K, where K is the permeability of the fibrous porous medium. Based on this finding, we modified the boundary condition in the Brinkman’s
solution and found that the velocity profile results compared well with the experimental data for the planar geometry and
the fibrous preforms for volume fractions of 7%, 14% and 21% for Hele–Shaw cell depths of 1.6 and 3.175 mm. For a cell depth
of 4.8 cm, in which the Hele–Shaw approximation was not valid, the boundary layer thickness or the screening length was found
to be less than the mold or channel depth but was still much larger than the Brinkman’s prediction.
Received: 10 May 1996 / Accepted: 26 August 1996 相似文献
12.
E. M. Shakhov 《Fluid Dynamics》2000,35(3):449-456
the steady two-dimensional isothermal rarefied flow in a channel formed by two parallel flat plates of finite length is studied
on the basis of the numerical solution of a linearized kinetic problem. The channel may either be isolated or constitute a
cell of a periodic cascade consisting of zero-thickness plates arranged one above the other. As the channel length increases,
the flow in it approaches the asymptotic one-dimensional Poiseuille flow. It is shown that the asymptotic dependence of the
gas flow rate on the low Knudsen number corresponding to an infinitely long channel is already attained for a channel of length
equal to several channel widths, if the flow rate is referred to the pressure gradient at the middle of the channel rather
than to the mean pressure difference at the channel ends. The effect of the boundary conditions imposed on the channel entrance
is investigated.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 166–175, May–June, 2000.
The study was carried out with the support of the Russian Foundation for Basic Research (project No. 98-01-00443). 相似文献
13.
An experimental investigation was carried out to study the enhancement of the heat transfer from a heated flat plate fitted
with rectangular blocks of 1 × 2 × 2 cm3 dimensions in a channel flow as a function of Reynolds number (Reh), spacing (S
y
) of blocks in the flow direction, and the block orientation angle (α) with respect to the main flow direction. The experiments were performed in a channel of 18 cm width and 10 cm height, with
air as the working fluid. For fixed S
x
=3.81 cm, which is the space between the blocks in transverse to the flow direction, the experimental ranges of the parameters
were S
y
=3.33–4.33 cm, α=0–45°, Reh=7625–31550 based on the hydraulic diameter and the average velocity at the beginning of the test section in the channel.
Correlations for Nusselt number were developed, and the ratios of heat transfer with blocks to those with no blocks were given.
The results indicated that the heat transfer could be enhanced or reduced depending on the spacing between blocks, and the
block orientation angle. The maximum heat transfer rate was obtained at the orientation angle of 45°.
Received on 13 December 2000 / Published online: 29 November 2001 相似文献
14.
The flow field downstream of a two-dimensional backward-facing step is usually assumed to be independent of the direction
along the span of the step. This assumption is made even though it is well known that the flow exhibits a three-dimensional
vortex structure. This state of affairs is no doubt due to the lack of detailed information concerning the characteristics
of the vortex structure. In this paper, we report our investigations of the flow structure around a reattachment region using
an ultrasound velocity profiler to measure the spanwise velocity component as a function of the spanwise coordinate and time.
The flow field is found to be very complex both in space and time. The low-frequency component of the spanwise velocity fluctuation
becomes dominant in the near-wall region, with peaks in the power spectrum at frequencies fh/Uc=0.05 and fh/Uc=0.012. Using multiple ultrasound transducers, we also find that a streamwise vortex exists in the flow.
Received: 20 March 2000 / Accepted: 15 January 2001 Published online: 29 November 2001 相似文献
15.
Image analysis applied to study on frictional-drag reduction by electrolytic microbubbles in a turbulent channel flow 总被引:1,自引:0,他引:1
We investigate frictional-drag reduction with electrolytic microbubbles based on image measurement of a turbulent flow in
a water channel at Re = 4800 (based on the half channel height). Microbubbles with a diameter ranging 30–200 μm can reduce frictional drag by as
much as 30% relative to single-phase flow even at low void fractions (α ≈ 3 × 10−4); however, drag reduction is only effective within a limited downstream distance from an electrode array. Arrangement of
the optical system allows us to measure the bubble-production rate by water electrolysis from images near the wall and to
trace the motion of bubbles. We also measure velocity fields using particle-tracking velocimetry based on a shallow depth-of-field
approach by segregating tracer particles from microbubbles. Vertically oscillating microbubbles likely represent interaction
with vortical structures near the wall, and bubbles approaching the wall appear to induce negative streamwise velocity relative
to the surrounding fluid. We relate the wall friction with the double integral of the Reynolds-stress profile and show that
its variation due to microbubbles decreases the drag on the wall. Microbubbles tend to coalesce downstream resulting in a
fewer bubbles but with greater size; accordingly, the oscillatory motion diminishes, and the frictional drag rather increases. 相似文献
16.
We describe how outer flow turbulence phenomena depend on the interaction with the wall. We investigate coherent structures
in turbulent flows over different wavy surfaces and specify the influence of the different surface geometries on the coherent
structures. The most important contribution to the turbulent momentum transport is attributed to these structures, therefore
this flow configuration is of large engineering interest. In order to achieve a homogeneous and inhomogeneous reference flow
situation two different types of surface geometries are considered: (1) three sinusoidal bottom wall profiles with different
amplitude-to-wavelength ratios of α = 2a/Λ = 0.2 (Λ = 30 mm), α = 0.2 (Λ = 15 mm), and α = 0.1 (Λ = 30 mm); and (2) a profile consisting of two superimposed sinusoidal
waves with α = 0.1 (Λ = 30 mm). Measurements are carried out in a wide water channel facility (aspect ratio 12:1). Digital
particle image velocimetry (PIV) is performed to examine the spatial variation of the streamwise, spanwise and wall-normal
velocity components in three measurement planes. Measurements are performed at a Reynolds number of 11,200, defined with the
half channel height h and the bulk velocity U
B. We apply the method of snapshots and perform a proper orthogonal decomposition (POD) of the streamwise, spanwise, and wall-normal
velocity components to extract the most dominant flow structures. The structure of the most dominant eigenmode is related
to counter-rotating, streamwise-oriented vortices. A qualitative comparison of the eigenfunctions for different sinusoidal
wall profiles shows similar structures and comparable characteristic spanwise scales Λ
z
= 1.5 H in the spanwise direction for each mode. The scale is observed to be slightly smaller for α = 0.2 (Λ = 15 mm) and slightly
larger for α = 0.2 (Λ = 30 mm). This scaling for the flow over the basic wave geometries indicates that the size of the largest
structures is neither directly linked to the solid wave amplitude, nor to the wavelength. The characteristic spanwise scale
of the dominant eigenmode for the developed flow over the surface consisting of two superimposed waves reduces to 0.85 H. However, a scale in the order of 1.3 H is identified for the second mode. The eigenvalue spectra for the superimposed waves is much broader, more modes contribute
to the energy-containing range. The turbulent flow with increased complexity of the bottom surface is characterized by an
increased number of dominant large-scale structures with different spanwise scales. 相似文献
17.
Summary The nonsimilar boundary-layer flow and heat transfer over a stationary permeable surface in a rotating fluid in the presence
of magnetic field, mass transfer and free stream velocity are studied. The parabolic partial differential equations governing
the flow have been solved numerically by using a difference–differential method. For small streamwise distance, these partial
differential equations are also solved by a perturbation technique with Shanks transformation. For uniform mass transfer,
analytical solutions are obtained. The surface skin friction coefficients and the Nusselt number increase with the magnetic
field, suction and streamwise distance from the leading edge of the plate except the skin friction coefficient in the y-direction which decreases with the increasing magnetic field.
Received 4 December 2001; accepted for publication 24 September 2002 相似文献
18.
Andrew J. Onstad Christopher J. Elkins Frank Medina Ryan B. Wicker John K. Eaton 《Experiments in fluids》2011,50(6):1571-1585
Open-celled foam geometries show great promise in heat/mass transfer, chemical treatment, and enhanced mixing applications.
Flow measurements on these geometries have consisted primarily of observations of the upstream and downstream effects the
foam has on the velocity field. Unfortunately, these observations give little insight into the flow inside the foam. We have
performed quantitative flow measurements inside a scaled replica of a metal foam, ϕ = 0.921, D
Cell = 2.5 mm, by Magnetic Resonance Velocimetry to better understand the fluid motion inside the foam and give an alternative
method to determine the foam cell and pore sizes. Through these 3-D, spatially resolved measurements of the flow field for
a cell Reynolds number of 840, we have shown that the transverse motion of the fluid has velocities 20–30% of the superficial
velocity passing through the foam. This strong transverse motion creates and dissipates streamwise jets with peak velocities
2–3 times the superficial velocity and whose coherence length is strongly correlated to the cell size of the foam. This complex
fluid motion is described as “mechanical mixing” and is attributed to the geometry of the foam. A mechanical dispersion coefficient,
D
M, was formed which demonstrates the transverse dispersion of this geometry to be 14 times the kinematic viscosity and 10 times
the thermal diffusivity of air at 20°C and 1 atm. 相似文献
19.
The effects of coincidence window and measuring volume size on two-component laser velocimeter measurement of turbulence
in an isothermal liquid flow through a concentric annular channel were studied. Three different coincidence windows (100–500 μs)
and three different measuring volume sizes (diameter, 5–9 wall units; spanwise length, 24–91 wall units) were used in a flow
of Reynolds number 31,500 and data density spanning the high end of intermediate to the low end of high (3–6). While no significant
effects of the coincidence window and measuring volume size were found on the time-mean velocity and turbulence intensities,
the streamwise Reynolds shear stress measured near a wall was found to be markedly affected by both. The smallest feasible
measuring volume along with an appropriate coincidence window provides good measurement of the shear stress.
Received: 8 September 1999/Accepted: 11 July 2000 相似文献
20.
S. V. Sukhinin 《Journal of Applied Mechanics and Technical Physics》1998,39(2):228-238
Acoustic eigenoscillations of a gas near a plate in a rectangular channel, i.e., the eigenfrequency of oscillations as a function
of the chord length and the position of the plate in the channel, and the form of the eigenfunctions are studied in a two-dimensional
formulation. A mathematical model of eigenoscillations near a plate in a channel has been proposed and substantiated, and
the dependence of the eigenfrequency of oscillations on the geometric parameters is studied numerically with the use of this
model.
Lavrent'ev Institute of Hydrodynamics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 2, pp. 78–90, March–April, 1998. 相似文献