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1.
The hydrodynamics of processes occurring in explosion of condensed explosives in air is considered. The physical model, computation
technique, and results of simulation of a two-dimensional hydrodynamic flow arising in explosion of cylindrical charges are
discussed. In this case, the explosions are considered at some distance above the ground. To close the gas-dynamics equations,
the Jones–Wilkins–Lee equation of state is used. The results of calculation allow one to obtain a detailed space–time pattern
of the arising flow and to study the origination, propagation, and subsequent attenuation of shock waves. Cylindrical charges
of the same mass but with different diameter-to-length ratios are considered. It is shown that the charge shape can render
essential influence on dynamics of flow and the parameters of shock waves (in the near and medium fields of explosion). 相似文献
2.
R. G. Galiullin É. R. Galiullina E. I. Permyakov 《Journal of Applied Mechanics and Technical Physics》1998,39(3):404-410
An analytical theory of resonant oscillations of a gas in an open-ended tube is developed. The gas flow in the tube is assumed
to be turbulent. A model of gas flow near the open end of the tube is constructed. This model allows a boundary condition
that is free of empirical parameters to be obtained. Theoretical results are in reasonable agreement with experimental data
obtained by other authors.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 92–99, May–June, 1998. 相似文献
3.
There is evidence from balloon measurements that atmospheric buoyancy–frequency profiles, apart from a sharp increase (roughly
by a factor of two) at the tropopause, often feature appreciable oscillations (typical wavelength 1–2 km) with altitude. It
is argued here that such short-scale oscillatory variations of the background buoyancy frequency, which usually are ignored
in theoretical models, can have a profound effect on the generation of mountain waves owing to a resonance mechanism that
comes into play at certain wind speeds depending on the dominant oscillation wavelength. A simple linear model assuming small
sinusoidal buoyancy–frequency oscillations suggests, and numerical solutions of the Euler equations for more realistic flow
conditions confirm, that under resonant conditions the induced gravity-wave activity is significantly increased above and
upstream of the mountain, similarly to resonant flow of finite depth over topography.
相似文献
4.
Near-resonance highly nonlinear ideal perfect gas oscillations in tubes are studied numerically for boundary conditions of
various types. The oscillations are initiated by weak periodic perturbations at one end of the tube. As distinct from earlier
studies [1–10], the oscillation amplitudes were not assumed to be small and the entropy increase at the shock waves formed
was taken into account. Periodic flow regimes result as a limit of the solution of a Cauchy problem for one-dimensional time-dependent
gasdynamic equations. The frequency responses of the oscillations under consideration are determined for boundary conditions
of various types. It is shown that in specific cases the attainment of a periodic regime is accompanied by the appearance
of long-wave modulations. The “repeated resonance” effect is revealed. This is due to the change in the tube's natural acoustic
frequency, which takes place during the heating of the gas in the tube by the shock waves traveling in it.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 150–157, July–August, 1994. 相似文献
5.
R.C. Mehta 《Shock Waves》2002,11(6):431-440
The pressure oscillations over a forward facing spike attached to an axisymmetric blunt body are simulated by solving time-dependent
compressible Navier–Stokes equations. The governing fluid flow equations are discretized in spatial coordinates employing
a finite volume approach which reduces the equations to semidiscretized ordinary differential equations. Temporal integration
is performed using the two-stage Runge–Kutta time stepping scheme. A global time step is used to obtain a time-accurate numerical
solution. The numerical computation is carried out for a freestream Mach number of 6.80 and for spike length to hemispherical
diameter ratios of 0.5, 1.0 and 2.0. The flow features around the spiked blunt body are characterized by a conical shock wave
emanating from the spike tip, a region of separated flow in front of the hemispherical cap, and the resulting reattachment
shock wave. Comparisons of the numerical results are made with the available experimental results, such as schlieren pictures
and the surface pressure distribution along the spiked blunt body. They are found to be in good agreement. Spectral analysis
of the computed pressure oscillations are performed employing fast Fourier transforms. The surface pressure oscillations over
the spike and phase plots exhibit a behaviour analogous to that of the Van der Pol equation for a self-sustained oscillatory
flow.
Received 28 February 2001 / Accepted 17 January 2002 相似文献
6.
A. N. Golovanov 《Journal of Applied Mechanics and Technical Physics》2006,47(5):637-642
A gas-dynamic flow in an axisymmetric convective jet is studied experimentally. It is demonstrated that the jet flow with
Grashof numbers Gr = (0.4–2.0) · 106 is self-similar. Acoustic oscillations directed perpendicular to the axis of symmetry transform the profiles of the gas-flow
parameters; two temperature maximums located outside the axis can appear. The results obtained indicate that flow instability
is generated in high-gradient regions.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 27–33, September–October, 2006. 相似文献
7.
Comparative evaluation of three heat transfer enhancement strategies in a grooved channel 总被引:1,自引:0,他引:1
Results of a comparative evaluation of three heat transfer enhancement strategies for forced convection cooling of a parallel
plate channel populated with heated blocks, representing electronic components mounted on printed circuit boards, are reported.
Heat transfer in the reference geometry, the asymmetrically heated parallel plate channel, is compared with that for the basic
grooved channel, and the same geometry enhanced by cylinders and vanes placed above the downstream edge of each heated block.
In addition to conventional heat transfer and pressure drop measurements, holographic interferometry combined with high-speed
cinematography was used to visualize the unsteady temperature fields in the self-sustained oscillatory flow. The locations
of increased heat transfer within one channel periodicity depend on the enhancement technique applied, and were identified
by analyzing the unsteady temperature distributions visualized by holographic interferometry. This approach allowed gaining
insight into the mechanisms responsible for heat transfer enhancement. Experiments were conducted at moderate flow velocities
in the laminar, transitional and turbulent flow regimes. Reynolds numbers were varied in the range Re = 200–6500, corresponding
to flow velocities from 0.076 to 2.36 m/s. Flow oscillations were first observed between Re = 1050 and 1320 for the basic
grooved channel, and around Re = 350 and 450 for the grooved channels equipped with cylinders and vanes, respectively. At
Reynolds numbers above the onset of oscillations and in the transitional flow regime, heat transfer rates in the investigated
grooved channels exceeded the performance of the reference geometry, the asymmetrically heated parallel plate channel. Heat
transfer in the grooved channels enhanced with cylinders and vanes showed an increase by a factor of 1.2–1.8 and 1.5–3.5,
respectively, when compared to data obtained for the basic grooved channel; however, the accompanying pressure drop penalties
also increased significantly.
Received on 5 April 2001 相似文献
8.
In this paper, the dynamics of two-dimensional cantilevered flexible plates in axial flow is investigated using a fluid–structure
interaction model. An additional spring support of either linear or cubic type is installed at various locations on the plate;
its presence qualitatively affects the dynamics of the fluid–structure system. Without the spring, the cantilevered plate
loses stability by flutter when the flow velocity exceeds a critical value; as the flow velocity increases further, the system
dynamics is qualitatively the same: the plate undergoes symmetric limit cycle oscillations with increasing amplitude. With
a linear spring, a state of static buckling is added to the dynamics. Rich nonlinear dynamics can be observed when a cubic
spring is considered; the plate may be stable and buckled, and it may undergo either symmetric or asymmetric limit cycle oscillations.
Moreover, when the flow velocity is sufficiently high, the plate may exhibit chaotic motions via a period-doubling route. 相似文献
9.
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
10.
A. E. Korenchenko O. A. Golovnya V. P. Beskachko 《Journal of Applied Mechanics and Technical Physics》2006,47(6):821-824
Results of a numerical solution of the problem of oscillations of an oscillating-cup viscometer filled with a viscoplastic
liquid are presented. It is shown that near the rotation axis, a stagnant zone arises, whose boundary changes position during
the oscillations. The effect of the plastic properties of the liquid on the frequency and damping coefficient of oscillations
of the viscometer is determined. A method of identifying the viscoplastic properties using observed oscillation parameters
is proposed.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 59–63, November–December, 2006. 相似文献
11.
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
12.
A linear and nonlinear analysis of the distributed oscillations of an elastic tube with a fluid flowing in it is developed.
The critical flow velocity and the wavelength and oscillation frequency in the tube-flow system at loss of stability are found.
The geometrical and physical nonlinearities, the latter related to increase in the Young’s modulus of the tube wall material
with increasing strain, are considered. It is shown that four characteristic regimes of change of tube shape are possible:
local dilatation, collapse, flexure, and distributed auto-oscillations. The tube oscillations are analyzed numerically for
the nonaxisymmetric case. The conditions of existence of these effects in blood vessels are examined.
Nizhni Novgorod, e-mail: klochkov@appl.sci-nnov.ru. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti
i Gaza, No. 4, pp. 46–55, July–August, 2000.
The work was supported by the Russian Foundation for Basic Research (project No. 97-02-18612). 相似文献
13.
Self-oscillating regimes of motion of a fluid close to Couette flow between rigid oppositely-rotating cylinders are investigated
in a small neighborhood of the point of intersection of the neutral curves of the monotonic and oscillating instabilities.
Bifurcation theory methods, together with computer calculations make it possible to detect transitions associated with the
generation of both quasiperiodic oscillations and chaotic attractors.
Rostov-on-Don. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 81–93, July–August,
1998. 相似文献
14.
S. V. Sukhinin 《Fluid Dynamics》2000,35(2):297-309
A model for the aeroacoustic resonance effects (aeolian tones) excited around a plate cascade in a gas flow is suggested.
Methods of calculating the frequencies of natural acoustic oscillations near the cascade are developed. The effect of the
cascade geometry and the Mach number of the main flow on the frequencies, abundance, and modes of the natural oscillations
is investigated. Anomalous acoustic oscillations near a cyclic plate cascade are shown to exist and are studied. It is shown
that there always exist no less than two natural oscillation frequencies in the gas flow near any nontrivial cyclic plate
cascade. It has been found that the natural oscillation frequencies can be combined in bundles such that in the case where
the number of plates in a period is large the frequencies pertaining to each bundle occupy a certain interval with arbitrary
density. The natural oscillations are classified with respect to the form of the eigenfunctions; the classification is based
on the theory of representations of groups of locally plane symmetries of the cyclic plate cascade in the solution space.
The correctness of the proposed model of the aeroacoustic resonance effects (aeolian tones) excited near a plate cascade in
a gas flow is supported by a comparison with the available experimental and theoretical data. On the basis of the investigation
performed, some previously unknown physical phenomena are predicted. Thus, the existence of frequency zones or main-flow Mach
number ranges on which aeroacoustic resonance phenomena exist near a cyclic cascade with a large number of plates in a period
is proved; it is shown that for certain frequencies of the natural oscillations near the cyclic plate cascade the resonance
oscillations may be localized in the vicinity of the source; and the existence of narrow-band wave packets slowly propagating
along the cascade is demonstrated.
Novosibirsk, e-mail: sukhinin@hydro.nsc.ru. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza,
No. 2, pp. 171–186, March–April, 2000. 相似文献
15.
A. G. Kuz’min 《Journal of Applied Mechanics and Technical Physics》2008,49(6):919-925
A turbulent flow past two symmetric airfoils, whose bow and aft portions are circular arcs, whereas midparts are flat, is
studies numerically. The amplitude of lift coefficient oscillations versus the free-stream Mach number M
∞
is analyzed at zero angle of attack. Ranges of M
∞
in which there exist flow bifurcations are determined.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 37–44, November–December, 2008 相似文献
16.
R. G. Zaripov R. I. Davydov N. V. Sonin 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1048-1050
Results of an experimental study of longitudinal nonlinear oscillations of a gas in a closed pipe are reported. Pressure waves
in a broad range of excitation amplitudes and frequencies are studied. Strong nonlinear oscillations at a frequency thrice
as low as the first natural frequency of the gas column are discovered.
Institute of Mechanics and Mechanical Engineering, Kazan' Scientific Center, Russian Academy of Sciences, Kazan' 420503. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 60–62, November–December, 1999. 相似文献
17.
An experimental study was conducted of incompressible, moderate Reynolds number flow of air over heated rectangular blocks
in a two-dimensional, horizontal channel. Holographic interferometry combined with high-speed cinematography was used to visualize
the unsteady temperature fields in self- sustained oscillatory flow. Experiments were conducted in the laminar, transitional
and turbulent flow regimes for Reynolds numbers in the range from Re = 520 to Re = 6600. Interferometric measurements were
obtained in the thermally and fluiddynamically periodically fully developed flow region on the ninth heated block. Flow oscillations
were first observed between Re = 1054 and Re = 1318. The period of oscillations, wavelength and propagation speed of the Tollmien–Schlichting
waves in the main channel were measured at two characteristic flow velocities, Re = 1580 and Re = 2370. For these Reynolds
numbers it was observed that two to three waves span one geometric periodicity length. At Re = 1580 the dominant oscillation
frequency was found to be around 26 Hz and at Re = 2370 the frequency distribution formed a band around 125 Hz. Results regarding
heat transfer and pressure drop are presented as a function of the Reynolds number, in terms of the block-average Nusselt
number and the local Nusselt number as well as the friction factor. Measurements of the local Nusselt number together with
visual observations indicate that the lateral mixing caused by flow instabilities is most pronounced along the upstream vertical
wall of the heated block in the groove region, and it is accompanied by high heat transfer coefficients. At Reynolds numbers
beyond the onset of oscillations the heat transfer in the grooved channel exceeds the performance of the reference geometry,
the asymmetrically heated parallel plate channel.
Received on 26 April 2000 相似文献
18.
In this work, the rectilinear Poiseuille flow of a complex liquid flowing in a vibrating pipe is analyzed. The pipe wall performs
oscillations of small amplitude that can be adequately represented by a weakly stochastic process, for which a quasi-static
perturbation solution scheme is suggested. The flow is analyzed using the Bautista–Manero–Puig constitutive equation, consisting
on the upper-convected Maxwell equation coupled to a kinetic equation to account for the breakdown and reformation of the
fluid structure. A drastic enhancement of the volumetric flow is predicted in the region where the fluid experiences pronounced
shear-thinning. Finally, flow enhancement is predicted using experimental data reported elsewhere for wormlike micellar solutions
of cetyl trimethyl ammonium tosilate. 相似文献
19.
Yu. A. Berezin L. A. Spodareva 《Journal of Applied Mechanics and Technical Physics》2000,41(4):699-706
The origination of wave motion on the surface of a thin layer of oil is studied. This layer is considered as an incompressible
pseudoplastic fluid, and surface tension is taken into account. It is shown analytically and numerically that these flows
may be stable or unstable depending on the value of the Ostwald number. Profiles of the free surface are found for various
values of the Ostwald and Weber numbers.
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No. 4, pp. 139–147, July–August, 2000. 相似文献
20.
R. I. Nigmatulin I. Sh. Akhatov N. K. Vakhitova 《Journal of Applied Mechanics and Technical Physics》1999,40(2):285-291
A spherically symmetric problem of oscillations of a single gas bubble at the center of a spherical flask filled with a compressible
liquid under the action of pressure oscillations on the flask wall is considered. A system of differential-difference equations
is obtained that extends the Rayleigh-Plesset equation to the case of a compressible liquid and takes into account the pressure-wave
reflection from the bubble and the flask wall. A linear analysis of solutions of this system of equations is performed for
the case of harmonic oscillations of the bubble. Nonlinear resonance oscillations and nearly resonance nonharmonic oscillations
of the bubble caused by harmonic pressure oscillations on the flask wall are analyzed.
Ufa Scientific Center, Russian Academy of Sciences, Ufa 450000. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 40, No. 2, pp. 111–118, March–April, 1999. 相似文献