共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
Adrian Renfer Manish K. Tiwari Thomas Brunschwiler Bruno Michel Dimos Poulikakos 《Experiments in fluids》2011,51(3):731-741
Hydrodynamics in microcavities with cylindrical micropin fin arrays simulating a single layer of a water-cooled electronic
chip stack is investigated experimentally. Both inline and staggered pin arrangements are investigated using pressure drop
and microparticle image velocimetry (μPIV) measurements. The pressure drop across the cavity shows a flow transition at pin
diameter–based Reynolds numbers (Re
d
) ~200. Instantaneous μPIV, performed using a pH-controlled high seeding density of tracer microspheres, helps visualize vortex
structure unreported till date in microscale geometries. The post-transition flow field shows vortex shedding and flow impingement
onto the pins explaining the pressure drop increase. The flow fluctuations start at the chip outlet and shift upstream with
increasing Re
d
. No fluctuations are observed for a cavity with pin height-to-diameter ratio h/d = 1 up to Re
d
~330; however, its pressure drop was higher than for a cavity with h/d = 2 due to pronounced influence of cavity walls. 相似文献
3.
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.
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Translated from PrikladnayaMekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 68–76, September–October, 2006. 相似文献
4.
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
5.
Laboratory measurements of wall pressure fluctuations and aerodynamic fields were made in separated flows over a forward facing
step (h = 30, 40 and 50 mm with U
e
= 15–40 m/s). An array of 16 off-set pressure probes extending in the streamwise and the spanwise directions was especially
developed for sensing the wall pressure fluctuations. The flow field was also investigated by wall flow visualizations and
PIV to analyze the flow topology in an open section wind tunnel. The results show a different behavior of the flow depending
on the aspect ratio l/h and δ/h for high Reynolds numbers. The space time correlations between the wall pressure and the velocity fields were highlighted.
The results show that high levels of these correlations are located at the top of the recirculation bubble, mainly in the
shear layer and are extended downstream of the re-attachment point. Indeed, the results indicate that the flapping motion
at the separation is important in the flow organization at the re-attachment point. 相似文献
6.
The characteristics of the flow and heat transfer in two- and three-dimensional open cavities on plane and cylindrical surfaces
in a supersonic stream in the presence of a turbulent boundary layer have been investigated experimentally. The effects of
the Mach number, boundary layer thickness, the shape of the cavity, and its angle of inclination to the free-stream direction
on the flow parameters in the mixing layer above the cavity and the heat flux and pressure distribution on the surface of
the cavity and its bottom are descirbed.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 74–80, July–August, 1998. 相似文献
7.
A. V. Reshetnikov V. I. Sannikov V. N. Skokov V. P. Koverda 《Journal of Applied Mechanics and Technical Physics》2007,48(1):7-10
Arc current fluctuations between a solid metal electrode and a liquid melt of alkaline carbonates at atmospheric pressure
are measured. Arc current fluctuation power spectra are determined from the measurement data. It is shown that the fluctuation
power is inversely proportional to the frequency (1/f-fluctuations). The fluctuations have a normal Gaussian distribution.
The observed 1/f fluctuations exhibit scale invariance.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 11–15, January–February, 2007. 相似文献
8.
Shiyao Bian James F. Driscoll Brian R. Elbing Steven L. Ceccio 《Experiments in fluids》2011,51(1):51-63
High Reynolds number, low Mach number, turbulent shear flow past a rectangular, shallow cavity has been experimentally investigated
with the use of dual-camera cinematographic particle image velocimetry (CPIV). The CPIV had a 3 kHz sampling rate, which was
sufficient to monitor the time evolution of large-scale vortices as they formed, evolved downstream and impinged on the downstream
cavity wall. The time-averaged flow properties (velocity and vorticity fields, streamwise velocity profiles and momentum and
vorticity thickness) were in agreement with previous cavity flow studies under similar operating conditions. The time-resolved
results show that the separated shear layer quickly rolled-up and formed eddies immediately downstream of the separation point.
The vortices convect downstream at approximately half the free-stream speed. Vorticity strength intermittency as the structures
approach the downstream edge suggests an increase in the three-dimensionality of the flow. Time-resolved correlations reveal
that the in-plane coherence of the vortices decays within 2–3 structure diameters, and quasi-periodic flow features are present
with a vortex passage frequency of ~1 kHz. The power spectra of the vertical velocity fluctuations within the shear layer
revealed a peak at a non-dimensional frequency corresponding to that predicted using linear, inviscid instability theory. 相似文献
9.
The purpose of this paper is to study the range of existence, the process of transition and the phase velocity of the spiral structure in an aspirated rotor–stator cavity. Experience shows that for a given flow rate and rotation, a whole range of azimuthal wave numbers are possible. Some are highly stable while others on the fringes of this range are subject to multiple transitions that depend on the fluctuations of the flow. Numerical simulation offers the advantage of enabling control over the wave number and the disturbance of the flow. Both approaches enable us to better understand the dynamics of this instability. 相似文献
10.
An exact solution is obtained to the three-dimensional problem of thermoelectroelasticity for a piezoceramic body with a spheroidal
cavity. The solutions of static thermoelectroelastic problems are represented in terms of harmonic functions. Far from the
cavity, the body is in a uniform heat flow perpendicular to the axis of symmetry of the cavity
__________
Translated from Prikladnaya Mekhanika, Vol. 41, No. 11, pp. 57–66, November 2005. 相似文献
11.
S. V. Osipov 《Journal of Applied Mechanics and Technical Physics》2008,49(5):781-788
This paper is concerned with mathematical modeling and solution of the problem of the collapse of a spherical cavity in a
viscoelastic medium under the action of constant pressure at infinity. A differential equation of motion for the cavity boundary
is constructed and solved numerically. The existence of three modes of motion of the boundary is established, and a map of
these modes in the plane of the determining parameters is constructed. Asymptotic forms of the solutions of the problem for
all modes are constructed. The problem of cavity collapse with capillary forces taken into account is formulated and solved.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 5, pp. 93–101, September–October, 2008. 相似文献
12.
Multiphase fluid dynamics and transport processes of low capillary number cavitating flows 总被引:1,自引:0,他引:1
Wei Shyy 《Acta Mechanica Sinica》2009,25(2):161-172
To better understand the multiphase fluid dynamics and associated transport processes of cavitating flows at the capillary number of 0.74 and 0.54, and to validate the numerical results, a combined computational and experimental investigation of flows around a hydrofoil is studied based on flow visualizations and time-resolved interface movement. The computational model is based on a modified RNG k-ε model as turbulence closure, along with a vapor-liquid mass transfer model for treating the cavitation process. Overall, favorable agreement between the numerical and experimental results is observed. It is shown that the cavi- tation structure depends on the interaction of the water-vapor mixture and the vapor among the whole cavitation stage, the interface between the vapor and the two-phase mixture exhibits substantial unsteadiness. And, the adverse motion of the interface relates to pressure and velocity fluctuations inside the cavity. In particular, the velocity in the vapor region is lower than that in the two-phase region. 相似文献
13.
Khalid N. Alammar 《Heat and Mass Transfer》2006,42(9):861-866
Using the standard k–ε turbulence model, a two-dimensional turbulent pipe flow was simulated with and without square cavities. Effect of cavity aspect ratio on flow and heat transfer characteristics was investigated. Uncertainty was approximated through experimental validation and grid independence. The simulation revealed circulation inside the cavities. Cavity boundaries were shown to contribute significantly toward turbulence production. Cavity presence was shown to enhance overall heat transfer through the wall, while increasing pressure drop significantly across the pipe. It was predicted that cavities with higher aspect ratio enhance heat transfer more while increasing pressure drop. 相似文献
14.
Laminar and turbulent computations are presented for annular rectangular-section cavities, on a body of revolution, in a Mach
2.2 flow. Unsteady ‘open cavity flows’ result for all laminar computations for all cavity length-to-depth ratios, L/D (1.33, 10.33, 11.33 and 12.33). The turbulent computations produce ‘closed cavity flows’ for L/D of 11.33 and 12.33. Surface pressure fluctuations at the front corner of the L/D = 1.33 cavity are periodic in some cases depending on the cavity length and depth, the boundary layer at the cavity front
lip and the cavity scale. The turbulent computations are supported by experimental schlieren images, obtained using a spark
light source, and time-averaged surface pressure data. 相似文献
15.
I. A. Bedarev Yu. A. Gosteev A. V. Fedorov 《Journal of Applied Mechanics and Technical Physics》2007,48(1):17-26
The dynamics of particles of the disperse phase in a turbulent gas flow in planar shock waves sliding along a solid surface
with a trapezoid cavity is examined numerically. Lifting of particles from the cavity walls is calculated in the approximation
of a rarefied gas suspension. It is shown that the intensity of the transient shock wave and the initial positions of particles
have a significant effect on the particle-lifting properties. The height of particle lifting is found to nonmonotonically
depend on the initial streamwise coordinate and shock-wave Mach number. It is shown that zones of aggregation and subtraction
of particles may be formed at the cavity bottom.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 24–34, January–February, 2007. 相似文献
16.
V. A. Mal'tsev S. A. Novopashin A. L. Perepelkin 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1057-1060
The effect of the flow character in the plenum chamber of a nozzle on the high-frequency boundary of the spectrum of fluctuations
at the boundary of a supersonic, strongly underexpanded jet of nitrogen exhausted from a circular sonic nozzle into the ambient
space was experimentally studied. The Reynolds number in the plenum chamber of the nozzle with a given throat area was varied
by changing the diameter of the subsonic region. The high-frequency boundary of the spectrum of turbulent fluctuations was
evaluated on the basis of two-point correlation functions of time. The technique for measurement of these functions was based
on molecular scattering of light. Radiation of two pulse lasers with a controlled delay between the pulses was used as a source
of light. It follows from experimental results that the high-frequency boundary of the spectrum of turbulent fluctuations
and the spectrum itself vary significantly depending on the Reynolds number of the flow in the plenum chamber.
Kutateladze Institute of Thermal Physics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from
Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 69–72, November–December, 1999. 相似文献
17.
K. N. Volkov 《Journal of Applied Mechanics and Technical Physics》2008,49(3):425-436
The motion and heat and mass transfer of particles of a disperse admixture in nonisothermal jets of a gas and a low-temperature
plasma are simulated with allowance for the migration mechanism of particle motion actuated by the turbophoresis force and
the influence of turbulent fluctuations of the jet flow velocity on heat and mass transfer of the particle. The temperature
distribution inside the particle at each time step is found by solving the equation of unsteady heat conduction. The laws
of scattering of the admixture and the laws of melting and evaporation of an individual particle are studied, depending on
the injection velocity and on the method of particle insertion into the jet flow. The calculated results are compared with
data obtained with ignored influence of turbulent fluctuations on the motion and heat and mass transfer of the disperse phase.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 95–108, May–June, 2008. 相似文献
18.
Delayed detached eddy simulation of the end-effect regime and side-loads in an overexpanded nozzle flow 总被引:2,自引:1,他引:1
Sébastien Deck 《Shock Waves》2009,19(3):239-249
The separated flow in an overexpanded nozzle featuring a restricted shock separation is investigated numerically using delayed
detached eddy simulation and compared with the experimental data of Nguyen et al. (Int J Flow Turbul Combust 71(1):161–181,
2003). First, the enormous cost of a Large Eddy Simulation for such a nozzle flow is assessed before being performed to motivate
the practical need for using an hybrid RANS/LES method. The calculation is then used to investigate the “end-effect” regime
which involves a strong global unsteadiness with very large amplitude fluctuations of about 15–20% of nozzle divergent length.
The flow regime is characterized by high wall pressure fluctuations which are hopefully nearly axisymmetric. The main properties
(rms levels, amplitude of displacement of the separation) of the motion are rather well reproduced by DDES compared to the
experiment. However, a major difference lies in the frequency of the computed motion which is higher than in the experiment.
This major discrepancy is currently not explained by the author. The properties of the side-loads are also briefly discussed.
相似文献
19.
K. N. Volkov 《Journal of Applied Mechanics and Technical Physics》2006,47(1):127-133
A turbulent flow in a closed axisymmetric cavity with a rotating disk is considered. The moment of resistance to disk rotation
is calculated as a function of the dimensionless gap between the motionless casing and rotating disk and of the Reynolds number.
Results calculated on the basis of different turbulence models are compared with data of a physical experiment and with available
correlations.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 1, pp. 153–160, January–February, 2006. 相似文献
20.
An array of microphones is used to study the space–time characteristics of the wall-pressure field beneath a forced separation
bubble downstream of an axi-symmetric backward-facing step. To excite the flow, an externally driven Helmholtz resonator is
employed. A unique aspect of the present study is the utilization of an amplitude-modulated forcing scheme in order to avoid
contamination of the measured hydrodynamic pressure fluctuations by acoustic radiation from the forcing device. The results lead to the hypothesis that the optimal forcing frequency is achieved when
the forced disturbance originates near the center of the unforced separation bubble in the limit of very low levels of forcing. Moreover, a frequency–wavenumber spectrum analysis highlights the possibility for achieving separation control while minimizing
potential acoustic radiation due to coupling between the forced disturbance and resonant modes of the underlying surface. 相似文献