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1.
Numerical investigation on the flowfield of "swallowtail" cavity for supersonic mixing enhancement 总被引:1,自引:0,他引:1
A "swallowtail" cavity for the supersonic combustor was proposed to serve as an efficient flame holder for scramjets by enhancing the mass exchange between the cavity and the main flow. A numerical study on the "swallow- tail" cavity was conducted by solving the three-dimensional Reynolds-averaged Navier-Stokes equations implemented with a k-e turbulence model in a multi-block mesh. Turbu- lence model and numerical algorithms were validated first, and then test cases were calculated to investigate into the mechanism of cavity flows. Numerical results demonstrated that the certain mass in the supersonic main flow was sucked into the cavity and moved spirally toward the combustor walls. After that, the flow went out of the cavity at its lateral end, and finally was efficiently mixed with the main flow. The comparison between the "swallowtail" cavity and the conventional one showed that the mass exchanged between the cavity and the main flow was enhanced by the lateral flow that was induced due to the pressure gradient inside the cavity and was driven by the three-dimensional vortex ring generated from the "swallowtail" cavity structure. 相似文献
2.
In this study, an integrated flow simulation and aeroacoustics prediction methodology is applied to testing a sound control
technique using porous inserts in an open cavity. Large eddy simulation (LES) combined with a three-dimensional Ffowcs Williams–Hawkings
(FW–H) acoustic analogy is employed to predict the flow field, the acoustic sources and the sound radiation. The Darcy pressure
– velocity law is applied to conceptually mimic the effect of porous media placed on the cavity floor and/or rear wall. Consequently,
flow in the cavity could locally move in or out through these porous walls, depending on the local pressure differences. LES
with “standard” subgrid-scale models for compressible flow is carried out to simulate the flow field covering the sound source
and near fields, and the fully three-dimensional FW–H acoustic analogy is used to predict the sound field. The numerical results
show that applying the conceptual porous media on cavity floor and/or rear wall could decrease the pressure fluctuations in
the cavity and the sound pressure level in the far field. The amplitudes of the dominant oscillations (Rossiter modes) are
suppressed and their frequencies are slightly modified. The dominant sound source is the transverse dipole term, which is
significantly reduced due to the porous walls. As a result, the sound pressure in the far field is also suppressed. The preliminary
study reveals that using porous-inserts is a promising technology for flow and sound radiation control. 相似文献
3.
This paper numerically simulates the forced convection flow in the developing region of a parallel-plate channel partially
filled with two porous substrates of equal thickness deposited at the inner walls of the channel. The major objective of the
present work is to investigate the impact of several operating and design parameters on the thermal performance of the channel
under consideration. The physical problem is simulated by using Darcy–Brinkman–Forchheimer model. For a prescribed amount
of porous material, the current investigation discusses the comparison between inserting this entire amount at one side of
the channel and inserting half of this amount at each side of the channel.
Received on 25 May 2000 / Published online: 29 November 2001 相似文献
4.
In this research the steady three-dimensional flow of a Walter’s B fluid in a vertical channel with porous wall, through which
the fluid is injected uniformly into the channel through one side of the channel, is studied analytically using Homotopy Analysis
Method (HAM). The channel is assumed to be infinite and uniform. The effects of the elasticity of the fluid on the flow and
heat transfer on the walls of the channel are discussed. 相似文献
5.
V. A. Vishnyakov V. G. Zasetskii R. K. Karavosov A. G. Prozorov L. I. Sokolinskii 《Fluid Dynamics》1998,33(2):238-244
The initiation of narrow-band pressure fluctuations in the duct of a pipeline gas-compression station when the flow is turned
near a blind-ended cavity was studied in a wind tunnel. The flow pattern under consideration was estimated from visualization
of the flow in a water channel using the hydraulic analogy technique. It is believed that the high-intensity narrow-band pressure
fluctuations observed in the flow result from the instability and regular rearrangement of large-scale vortex structures in
the blind-ended cavity.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 104–111, March–April, 1998. 相似文献
6.
A. Yu. D’yachenko V. I. Terekhov N. I. Yarygina 《Journal of Applied Mechanics and Technical Physics》2006,47(5):671-678
The process of vortex formation in a cavity with inclined walls, which has a moderate aspect ratio, is experimentally studied,
and the distribution of pressure coefficients is measured. The angle of inclination of the side walls ϕ is varied from 30
to 90°. It is found that the flow in the cavity becomes unstable in the range of inclination angles ϕ = 60–70°. Flow reconstruction
occurs, which substantially alters the surface-temperature and static-pressure distributions. Large changes in these characteristics
and their nonuniform distributions for these angles are observed across the cavity on its frontal wall and on the bottom.
For small angles (ϕ = 30 and 45°), the pressure on the rear wall drastically increases, which leads to a small increase in
pressure averaged over the entire cavity surface.
__________
Translated from PrikladnayaMekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 68–76, September–October, 2006. 相似文献
7.
M. Turkyilmazoglu J.W. Cole J.S.B. Gajjar 《Theoretical and Computational Fluid Dynamics》2000,14(1):21-37
A numerical study has been undertaken to investigate the nature of inviscid instability of the three-dimensional compressible
boundary layer flow due to a rotating disk. The compressible Rayleigh equation is integrated using a spectral Chebyshev-collocation
method together with a fourth-order Runge–Kutta integrator. In the context of spatio-temporal stability analysis, the singularities
of the resulting dispersion relation are determined and the ones that satisfy the Briggs–Bers pinching criterion have been
selected. In certain finite parameter regions of eigenvalues (wave numbers and wave angles, for instance) it is found that
by varying the Mach number, absolute instability occurs in the compressible boundary layer on a rotating disk. The range corresponding
to the incompressible flow case given in Lingwood (1995) (ε between 14.615° and 38.114°) is verified. The results of Cole
(1995) are also verified. The overall effect of compressibility is to reduce the extent of absolute instability at higher
Mach numbers. The effect of heating the wall is to enhance the absolute instability properties, however, cooling the wall
is found to decrease greatly the region of absolute instability regime for the range of Mach numbers studied. It is also shown
in this study that for non-insulated walls a direct spatial resonance of the eigenmodes is possible and this raises the possibility
of large local algebraic growth of perturbations being important in some instances.
Received 15 October 1999 and accepted 10 December 1999 相似文献
8.
Sergey A. Suslov 《Theoretical and Computational Fluid Dynamics》2007,21(4):271-290
The problem of non-Boussinesq mixed convection in a vertical channel formed by two differentially heated infinite plates is
investigated and the complete convective/absolute instability boundary is computed for a wide range of physical parameters.
A physical insight into the mechanisms causing instabilities is given. In particular, it is shown that the appearance of absolute
instability is always dictated by a flow reversal within a channel; however, existence of the flow reversal does not exclude
the possibility of convective instability. It is also shown that fluid’s non-linear transport property variations have a dramatic
effect on the structure and complexity of spatio-temporal instabilities of the co-existing buoyancy and shear modes as the
temperature difference across the channel increases. The validity of the stability results obtained using the procedure described
in Suslov (J Comp Phys 212, 188–217, 2006) is assessed using the method of steepest descent.
This work was partially supported by a computing grant from the Australian Partnership for Advanced Computing, 2000–2003. 相似文献
9.
A numerical study of mixed convection in a vertical channel filled with a porous medium including the effect of inertial forces
is studied by taking into account the effect of viscous and Darcy dissipations. The flow is modeled using the Brinkman–Forchheimer-extended
Darcy equations. The two boundaries are considered as isothermal–isothermal, isoflux–isothermal and isothermal–isoflux for
the left and right walls of the channel and kept either at equal or at different temperatures. The governing equations are
solved numerically by finite difference method with Southwell–Over–Relaxation technique for extended Darcy model and analytically
using perturbation series method for Darcian model. The velocity and temperature fields are obtained for various porous parameter,
inertia effect, product of Brinkman number and Grashof number and the ratio of Grashof number and Reynolds number for equal
and different wall temperatures. Nusselt number at the walls is also determined for three types of thermal boundary conditions.
The viscous dissipation enhances the flow reversal in the case of downward flow while it counters the flow in the case of
upward flow. The Darcy and inertial drag terms suppress the flow. It is found that analytical and numerical solutions agree
very well for the Darcian model.
An erratum to this article is available at . 相似文献
10.
P. D. Weidman 《Heat and Mass Transfer》2006,43(2):103-109
In a recent publication Bühler (Heat Mass Transfer 39:631–638, 2003) reported new results for conduction regime flow between vertical differentially-heated walls that provide a continuum of solutions between capped and open ends. In this paper we extend Bühler’s work to realize a continuum of solutions of convection regime flow using empirical results for the vertical temperature gradient that develops in tall aspect ratio geometries. The mass flux is determined analytically for this three-parameter family of solutions. Identical viscous and thermal boundary layers exist at the opposing walls when the cavity is capped. However, as the flow evolves to one with open ends, there is an intensification (attenuation) of the boundary layers near the hot (cold) walls. In the limit corresponding to an open-ended cavity, the boundary layer at the cold wall vanishes altogether. 相似文献
11.
Numerical simulation of Poiseuille flow of liquid Argon in a nanochannel using the non-equilibrium molecular dynamics simulation
(NEMD) is performed. The nanochannel is a three-dimensional rectangular prism geometry where the concerned numbers of Argon
atoms are 2,700, 2,550 and 2,400 at 102, 108 and 120 K. Poiseuille flow is simulated by embedding the fluid particles in a
uniform force field. An external driving force, ranging from 1 to 11 PN (Pico Newton), is applied along the flow direction
to inlet fluid particles during the simulation. To obtain a more uniform temperature distribution across the channel, local
thermostating near the wall are used. Also, the effect of other mixing rules (Lorenthz–Berthelot and Waldman–Kugler rules)
on the interface structure are examined by comparing the density profiles near the liquid/solid interfaces for wall temperatures
108 and 133 K for an external force of 7 PN. Using Kong and Waldman–Kugler rules, the molecules near the solid walls were
more randomly distributed compared to Lorenthz–Berthelot rule. These mean that the attraction between solid–fluid atoms was
weakened by using Kong rule and Waldman–Kugler rule rather than the Lorenthz–Berthelot rule. Also, results show that the mean
axial velocity has symmetrical distribution near the channel centerline and an increase in external driving force can increase
maximum and average velocity values of fluid. Furthermore, the slip length and slip velocity are functions of the driving
forces and they show an arising trend with an increase in inlet driving force and no slip boundary condition is satisfied
at very low external force (<1 PN). 相似文献
12.
Tanja Siegmann-Hegerfeld Stefan Albensoeder Hendrik C. Kuhlmann 《Experiments in fluids》2013,54(6):1-9
The flow in a lid-driven cavity with width-to-height ratio of 1.6 is investigated numerically and experimentally. Experimental investigation use an apparatus with a spanwise length-to-height ratio of $\Uplambda = 10.85.$ Λ = 10.85 . Increasing the Reynolds number, we experimentally find a gradual change from the quasi-two-dimensional basic flow to a three-dimensional flow pattern. The three-dimensional flow has a significant amplitude at considerably low Reynolds numbers. Streak-line photographs and PIV vector maps are presented to illustrate the structure of the finite-amplitude flow pattern. The smooth transition is in contrast to the linear instability predicted by a linear-stability analysis for a cavity with infinite span. LDV measurements confirm the absence of a distinct threshold Reynolds number and indicate an imperfect bifurcation. The deviations between experimental observations and numerical critical Reynolds number for infinite span are explained by conducting three-dimensional simulations for a finite-span geometry. A good agreement between experimental and numerical simulation is obtained. The numerical and experimental data lead to the conjecture of a premature onset of the three-dimensional flow caused by strong secondary flows which are induced by the cavity end walls. Nevertheless, the flow structure in the finite-span cavity carries the same characteristic signatures as the nonlinear flow in the corresponding infinite-length cavity. We conclude that the observed flow can be identified as the continuation of the normal mode C e 4 earlier identified in a linear-stability analysis. 相似文献
13.
H. M. Badr M. A. Habib R. Ben-Mansour S. A. M. Said T. F. Ayinde S. Anwar 《Heat and Mass Transfer》2011,47(11):1427-1443
This paper presents the results of experimental and numerical investigations of the problem of turbulent natural convection
in a converging-plate vertical channel. The channel has two isothermally heated inclined walls and two adiabatic vertical
side walls. The parameters involved in this study are the channel geometry represented by the channel width at exit, the inclination
of the heated walls and the temperature difference between the heated walls and the ambient. The investigation covered modified
Rayleigh numbers up to 108 in the computational study and up to 9.3 × 106 in the experimental work. The experimental measurements focused on the velocity field and were carried out using a PIV system
and included measurements of the mean velocity profiles as well as the root-mean-square velocity and shear stress profiles.
The experiments were conducted for an inclination angle of 30°, a gap width of 10 mm and two temperature differences (∆T=25.4°C
and 49.8°C). The velocity profiles in the lower part of the channel indicated the presence of two distinct layers. The first
layer is adjacent to the heated plate and driven by buoyancy forces while the second layer extends from the point of maximum
velocity to the channel center plane and driven mainly by shear forces. The velocity profile at the upper portion of the channel
has shown the merging of the two boundary layers growing over the two heated walls. The measured values of the Reynolds shear
stress and root mean square of the horizontal and vertical velocity fluctuation components have reached their maximum near
the wall while having smaller values in the core region. The computational results have shown that the average Nusselt number
increases approximately linearly with the increase of the modified Rayleigh number when plotted on log–log scale. The variation
of the local Nusselt number indicated infinite values at the channel inlet (leading edge effect) and high values at the channel
exit (trailing edge effect). For a fixed value of the top channel opening, the increase of the inclination angle tended to
reduce flow velocity at the inlet section while changing the flow structure near the heated plates in such a way to create
boundary-layer type flow. The maximum value of the average Nusselt number occurs when θ = 0 and decreases with the increase
of the inclination angle. On the other hand, the increase of the channel width at exit for the same inclination angle caused
a monotonic increase in the flow velocity at the channel inlet. 相似文献
14.
M. V. D’Angelo B. Semin G. Picard M. E. Poitzsch J. P. Hulin H. Auradou 《Transport in Porous Media》2010,84(2):389-408
The transport of fibers by a fluid flow is investigated in transparent channels modeling rock fractures: the experiments use
flexible polyester thread (mean diameter 280 μm) and water or a water–polymer solution. For a channel with smooth parallel walls and a mean aperture ā = 0.65 mm, both fiber segments of length ℓ = 20–150 mm and “continuous” fibers longer than the channel length have been used: in both the cases, the velocity of the
fibers and its variation with distance could be accounted for while neglecting friction with the walls. For rough self-affine
walls and a continuous gradient of the local mean aperture transverse to the flow, transport of the fibers by a water flow
is only possible in the region of larger aperture (ā ≲ 1.1 mm) and is of “stop and go” type at low velocities. With the polymer solution, the fibers move faster and more continuously
in high aperture regions and their interaction with the walls is reduced; fiber transport becomes also possible in narrower
regions where irreversible pinning occurred for water. In a third rough model with parallel walls and a low mean aperture
ā = 0.65 mm, fiber transport is only possible with the water–polymer solution. The dynamics of fiber deformations and entanglement
during pinning–depinning events and permanent pinning is analyzed. 相似文献
15.
We study global asymptotic behavior of Poisson–Nernst–Planck (PNP) systems for flow of two ion species through a narrow tubular-like
membrane channel. As the radius of the cross-section of the three-dimensional tubular-like membrane channel approaches zero,
a one-dimensional limiting PNP system is derived. This one-dimensional limiting system differs from previously studied one-dimensional
PNP systems in that it encodes the defining geometry of the three-dimensional membrane channel. To justify this limiting process,
we show that the global attractors of the three-dimensional PNP systems are upper semi-continuous as the radius of the channel
tends to zero. 相似文献
16.
This paper is concerned with a liquid metal flow driven by a rotating magnetic field inside a stationary cylinder. We consider
especially the secondary meridional flow during the time when the fluid spins up from rest. The developing flow is investigated
experimentally and by direct numerical simulations. The vertical profiles of the axial velocity are measured by means of the
ultrasound Doppler velocimetry. Evolving instabilities in the form of Taylor–G?rtler vortices have been observed just above
the instability threshold (Ta ≥ 1.5· Ta
cr). The rotational symmetry may survive over a distinct time even if a first Taylor–G?rtler vortex pair has been formed as
closed rings along the cylinder perimeter. The transition to a three-dimensional flow in the side layers results from the
advection or a precession and splitting of the Taylor–G?rtler vortex rings. The predictable behaviour of the Taylor–G?rtler
vortices disappears with increasing magnetic field strength. The numerical simulations agree very well with the flow measurements. 相似文献
17.
Two-dimensional particle image velocimetry (PIV) is used to obtain a set of parallel vector maps in spanwise direction over
the delta wing configuration ELAC. The out-of-plane velocity component is then constructed by application of continuity equation.
This yields the whole three-dimensional separated flow field over the leeward side of the model. The spatial resolution of
the measurements enables a detailed examination of the three-dimensional flow structure. The growth and the helical structure
of primary vortex as well as smaller flow structures caused by secondary separation can be observed. Accuracy of the constructed
velocity component is estimated with help of a numerically obtained three-dimensional dataset of the flow field around this
configuration. The reconstruction procedure was applied to this data set taking the experimental uncertainty and the grid
spacing of the PIV measurements into consideration. A comparison of reconstructed out-of-plane component and data of the numerical
solution of Navier–Stokes equations results in a promising low error. A statistical analysis of different procedures allows
interpretation of reconstruction capabilities.
Received: 15 April 1998 / Accepted: 15 September 1998 相似文献
18.
《European Journal of Mechanics - B/Fluids》2002,21(3):307-316
The linear stability of two counter-rotating vortices driven by the parallel motion of two facing walls in a rectangular cavity is investigated by a finite volume method. Critical Reynolds and wave numbers are calculated for aspect ratios ranging from 0.1 to 5. This range is sufficient to find the asymptotic behavior of the critical parameters when the aspect ratio tends to zero and infinity, respectively. The critical curve is smooth for all aspect ratios and, hence, the character of the instability changes continuously. When the moving walls are far apart the mechanism is centrifugal, as in the classical lid-driven cavity. For aspect ratios near unity a combined mechanism, also involving strain near the vortex cores, leads to the instability which tends to asymmetrically displace the vortex cores, very similar to the cooperative short-wave instability of a free counter-rotating vortex pair. In the limit when plane Poiseuille flow is approached in the bulk, the three-dimensional perturbations are strongly localized near both downstream ends of the moving walls. 相似文献
19.
J. Prathap Kumar J. C. Umavathi I. Pop Basavaraj M. Biradar 《Transport in Porous Media》2009,80(1):117-135
An analysis of fully developed combined free and forced convective flow in a fluid saturated porous medium channel bounded
by two vertical parallel plates is presented. The flow is modeled using Brinkman equation model. The viscous and Darcy dissipation
terms are also included in the energy equation. Three types of thermal boundary conditions such as isothermal–isothermal,
isoflux–isothermal, and isothermal–isoflux for the left–right walls of the channel are considered. Analytical solutions for
the governing ordinary differential equations are obtained by perturbation series method. In addition, closed form expressions
for the Nusselt number at both the left and right channel walls are derived. Results have been presented for a wide range
of governing parameters such as porous parameter, ratio of Grashof number and Reynolds number, viscosity ratio, width ratio,
and conductivity ratio on velocity, and temperature fields. It is found that the presence of porous matrix in one of the region
reduces the velocity and temperature. 相似文献
20.
The three-dimensional stationary instability in dynamic thermocapillary shallow cavities 总被引:4,自引:0,他引:4
In various configurations with thermal convection, three-dimensional stationary patterns occur that consist of pairs of counter-rotating
longitudinal rolls. These rolls are investigated in this paper under a variety of experimental conditions. The liquids used
are ethanol and the silicone oil hexamethyldisiloxane. The upper surface of the liquid volume is free and very flat because
measures against menisci at the side and end walls have been taken. The temperature gradient is applied horizontally via thermally
conducting but transparent sapphire end walls, leading to thermocapillary forces at the free surface in addition to the buoyant
forces at normal earth's gravity. The geometry of the liquid volume is either rectangular or axisymmetrical (annular). The
rectangular set-up is transparent and especially suited for optical observations of tracers in the bulk of the liquid. The
annular set-up has the advantages of a large azimuthal (transversal) extent and the absence of side walls. In it a wavelength
of λ≈1.3d was observed (where d is the depth of the liquid volume). Temperatures and velocities are measured and used to characterize the instability. Also
the region of existence of the instability is studied in layers shallower than in earlier experiments in order to give a larger
ratio between thermocapillary and buoyant forces. To find the onset of the instability when increasing the temperature gradient,
the amplitude of the instability was derived from measurements and extrapolated. This yields a significantly lower threshold
(Mac=2300 ± 1000 for d=5 mm) than previous experimental studies. One implementation of the annular gap experiment was performed under microgravity
(experiment MAGIA), the other experiments under normal gravity. The results of the experiment under microgravity indicate
the absence of the three-dimensional stationary pattern under the absence of gravity.
Received: 14 August 2000/Accepted: 17 April 2001 相似文献