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1.
This paper presents an experimental investigation of one-dimensional moving shock waves in vertical soap films. The shock
waves were generated by bursting the films with a perforating spark. Images of propagating shock waves and small disturbances
were recorded using a fast line scan CCD camera. An aureole and a shock wave preceding the rim of the expanding hole were
clearly observed. These images are similar to the x-t diagrams in gas dynamics and give the velocities of shock and sound waves. The moving shock waves cause jumps in thickness.
The variations of the induced Mach number, M2 and the ratio of film thickness across the shock wave, δ
2/δ
1, are plotted versus the shock Mach number, M
s. Both results suggest that soap films are analogous to compressible gases with a specific heat ratio of γ≅1.0.
Published online: 15 October 2002 相似文献
2.
The interaction between a normally impinging shock wave and the boundary layer on a plate with slip is studied in the neighborhood
of the leading edge using various experimental methods, including special laser technology, to visualize the supersonic conical
gas flows. It is found that in the “non-free” interaction, when the leading edge impedes the propagation of the boundary layer
separation line upstream, the structure of the disturbed flow is largely identical to that in the developed “free” interaction,
but with higher parameter values and gradients in the leading part of the separation zone. The fundamental property of developed
separation flows, namely, coincidence of the values of the pressure “plateau” in the separation zone and the pressure behind
the oblique shock above the separation zone of the turbulent boundary layer, is conserved.
Moscow. e-mail: ostap@inmech.msu.su. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3,
pp. 57–69, May–June, 2000.
The work was carried out with financial support from the Russian Foundation for Basic Research (project No. 97-01-00099). 相似文献
3.
4.
The nonequilibrium radiation of shock fronts in air is experimentally investigated by means of the imaging spectroscopy technique.
Shock velocity ranges from 9.7 to 11.6 km/s and initial pressure from 13.3 to 41.6 Pa. The spectral diagnostic system consists
of an imaging spectrograph, a streak camera, a gated image-intensified CCD camera and a personal computer for data acquisition/processing.
This spectral diagnostic system is capable of simultaneous wavelength-, intensity- and time-resolved spectroscopic measurements
in the nanosecond order. The image processing of the streak images includes a combined smoothing/deconvolution process in
the time direction to diminish experimental noise effects and the temporal broadening due to the streak camera entrance slit.
Wavelength range is chosen to investigate the first negative band of . “Large” and “slim” streak image types are observed. In the “large” streak images greater contribution from (1-)(1,0) behind the radiation peak is observed. Experimental data are compared with a streak image numerically simulated.
The numerical simulation agrees better with the “slim” streak image.
Received 7 July 1995 / Accepted 10 January 1996 相似文献
5.
K. Prestridge P. M. Rightley P. Vorobieff R. F. Benjamin N. A. Kurnit 《Experiments in fluids》2000,29(4):339-346
We describe a highly-detailed experimental characterization of the Richtmyer-Meshkov instability (the impulsively driven
Rayleigh-Taylor instability) (Meshkov 1969; Richtmyer 1960). In our experiment, a vertical curtain of heavy gas (SF6) flows into the test section of an air-filled, horizontal shock tube. The instability evolves after a Mach 1.2 shock passes
through the curtain. For visualization, we pre-mix the SF6 with a small (∼10−5) volume fraction of sub-micron-sized glycol/water droplets. A horizontal section of the flow is illuminated by a light sheet
produced by a combination of a customized, burst-mode Nd:YAG laser and a commercial pulsed laser. Three CCD cameras are employed
in visualization. The “dynamic imaging camera” images the entire test section, but does not detect the individual droplets.
It produces a sequence of instantaneous images of local droplet concentration, which in the post-shock flow is proportional
to density. The gas curtain is convected out of the test section about 1 ms after the shock passes through the curtain. A
second camera images the initial conditions with high resolution, since the initial conditions vary from test to test. The
third camera, “PIV camera,” has a spatial resolution sufficient to detect the individual droplets in the light sheet. Images
from this camera are interrogated using Particle Image Velocimetry (PIV) to recover instantaneous snapshots of the velocity
field in a small (19 × 14 mm) field of view. The fidelity of the flow-seeding technique for density-field acquisition and
the reliability of the PIV technique are both quantified in this paper. In combination with wide-field density data, PIV measurements
give us additional physical insight into the evolution of the Richtmyer-Meshkov instability in a problem which serves as an
excellent test case for general transition-to-turbulence studies.
Received: 26 June 1999/Accepted: 29 October 1999 相似文献
6.
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
7.
Results are presented from an experimental investigation into the interaction of a planar shock wave with a vortex ring. A
free-falling spherical soap bubble is traversed by the incident shock wave and develops into a vortex ring as a result of
baroclinically deposited vorticity (?r×?p 1 0{\nabla\rho\times\nabla p \neq 0}). The vortex ring translates with a velocity relative to the particle velocity behind the shock wave due to circulation.
After the shock wave reflects from the tube end wall, it traverses the vortex ring (this process is called “reshock”) and
deposits additional vorticity. Planar Mie scattering is used to visualize the atomized soap film at high frame rates (up to
10,000 fps). Particle image velocimetry (PIV) was performed for an argon bubble in nitrogen accelerated by a M = 1.35 shock wave. Circulation was determined from the PIV velocity field and found to agree well with Kelvin’s vortex ring
model. 相似文献
8.
An algorithm is derived for calculating flow-induced birefringence using a bead-spring model with and without excluded volume
effects. The simulation results for the bead-spring model compare well with experimental results for stress and birefringence
in extensional flows of dilute solutions of polystyrene molecular weight 2 million in a filament-stretching device in both
“theta” and “good” solvents (Orr and Sridhar 1999; Sridhar et al. 2000). In a “good” solvent, both stress and birefringence
rise much more rapidly with strain than in a “theta” solvent, making extensional rheology a very sensitive indicator of solvent
quality.
Received: 7 December 1999 Accepted: 23 May 2000 相似文献
9.
N. L. Efremov A. N. Kraiko K. S. Pyankov N. I. Tillyaeva E. A. Yakovlev 《Fluid Dynamics》2010,45(2):289-304
We study shock wave structures (SWS), consisting of shock waves and expansion waves between them, that occur in supersonic
flow past nonuniform fan cascades when the velocity component normal to their front (“axial” component) is subsonic. The cascade
nonuniformity is due to the scatter in the setting angles of identical blades, either sharp or blunt. A result of the uniformity
is the generation of combined noise, whose frequencies are much smaller than the fundamental frequency of the uniform cascade,
and slower nonlinear SWS attenuation. The accurate and fast “simple wave method” and “nonlinear acoustics approximation”,
together with numerical algorithms for integrating Euler equations on overlapping grids (in calculating flow past blunt edges)
and on SWS-adapted grids, are applied to determine the “guiding” action of nonuniform cascades and to describe the SWS evolution.
The application of the Fourier analysis gives the sound field spectrum. The use of blades with rectilinear initial regions
of the “backs” for reducing supersonic fan blade noise is efficient only at small (less than 0.25°) scatter in the setting
angles. The shock wave structures attenuate more rapidly ahead of nonuniform cascades composed of blunt blades than ahead
of those with sharp blades. For uniform cascades the blade bluntness effect is not large. 相似文献
10.
N. J. Dam M. Rodenburg R. A. L. Tolboom G. G. M. Stoffels P. M. Huisman-Kleinherenbrink J. J. ter Meulen 《Experiments in fluids》1998,24(2):93-101
Rayleigh scattering of ultra-violet laser light is applied as a diagnostic tool to record gas density distributions in a
supersonic nozzle flow. The output beam of a pulsed ArF excimer laser (λ=193.4 nm) is focussed into a thin light sheet radially
intersecting a dry air flow emanating from a circular nozzle. An intensified CCD camera is used to record the Rayleigh scattered
light in a direction perpendicular to the light sheet. Since the Rayleigh scattering intensity is directly proportional to
the local gas density, this results in two-dimensional gas density distribution maps of radial slices through the flow. Images
of the flow density are presented for stagnation pressures between 0.2 and 0.7 MPa (0.1 MPa ≡1 bar), showing the transition
from subsonic to supersonic flow and, at higher pressures, the formation of a Mach disk. Density maps can be recorded with
single laser pulses, effectively freezing the flow structure on a 20 ns time scale. The diamond pattern, characteristic for
underexpanded supersonic nozzle flows, is quantitatively monitored, with the experimental results being in reasonable agreement
with predictions from a simplified theoretical model.
Received: 25 September 1996/Accepted: 19 May 1997 相似文献
11.
The authors have carried out a study to investigate and clarify the characteristics of purely oscillating pipe flows over
the developing region. The main objective of this study is to establish the method of time-dependent velocity profiles obtained
by the ultrasonic velocity profile (UVP) measurement method. First, the relationship between the test fluids and the microparticles,
as reflectors of ultrasonic pulses, was investigated. In addition, the relationship between the sound speeds of the test fluids
and the wall materials was studied. Second, the UVP was used to obtain the instantaneous velocity profiles in oscillating
pipe flows, and the developing characteristics of the flows were analyzed. Finally, the “entrance length” (by analogy with
a unidirectional pipe flow) required for oscillating pipe flows was analyzed by examining the amplitude of the harmonic spectral
components of the oscillating frequency. A fast Fourier transform (FFT) is proposed as the applicable method to estimate the
“entrance length”. From the Fourier transform of the velocity on the centerline, nonlinear oscillation of fluid occurs in
the “entrance length” of the oscillating flows, and the viscous dissipation of the higher-order velocity harmoncis determines
the entrance region. The “entrance length” can be obtained from the dissipation length of the third-order harmonic. These
results prove that the UVP method is highly applicable to carry out the flow measurement in the “entrance length” of oscillating
pipe flow.
Received: 20 March 2000 / Accepted: 10 August 2001 相似文献
12.
A supersonic exhaust plume test rig and a Rayleigh scattering system were developed. Molecular number densities in the supersonic
high-temperature exhaust plume with and without an annular base flow were investigated. The physical meaning of the inferred
mean temperature from the number density measurement in turbulent flows is clarified. For both flows, the potential core extends
up to about six nozzle diameters, and self-similarity of the radial density distributions is observed at downstream sections
Z/d=10–50. The recovery of the flow density deficit (or the decay of temperature) with the annular flow is faster than that without
the annular flow at upstream sections Z/d ≤ 10.
Received: 16 August 2000 / Accepted: 20 November 2001 相似文献
13.
Summary Reflected and transmitted pressure waves take place when an incident pressure wave reaches a screen placed in a duct and crossed
by a previous steady flow.
The thickness of the screen is assumed to be negligible and essure losses through it in the quasi steady flow, which takes
place after the passage of the incident pressure wave, are assumed be steady flow ones.
The strength of reflected and transmitted pressure waves is related to the strength of the incident wave, to the porosity
of the screen and to the previous flow through it. Subsonic and just supersonic quasi steady flow inside the screen are considered.
Five commercial screens have been tested with incident shock waves and the experimental results have been compared with the
theoretical ones: the agreement is quite satisfactory.
The present work has been supported by the “Consiglio Nazionale delle Ricerche” (C.N.R.) under Contract no. 115.4075.69.01220.
The suffixes “u” and “d” pertain to the conditions upstream and downstream of the screen with reference to the flow through it. The suffix “j” refers to the region “j” of the wave diagrams in Fig. 1. 相似文献
Sommario L'interazione di un'onda di pressione con una rete intubata attraversata da un flusso preesistente produce un'onda riflessa ed una trasmessa. Si presenta un modello teorico basato essenzialmente sulle potesi che lo spessore della rete sia trascurabile e che le perdite carico attraverso di essa, nel flusso quasi stazionario indotto dalla suddetta interazione, coincidano con quelle proprie di un oto permanente. Si analizza il caso di flusso indotto nella rete ia subsonico che sonico. Si eseguono prove sperimentali su cinque reti di diverse porosità differenti condizioni di flusso, e si verifica l'attendibilità del odello teorico proposto.
The present work has been supported by the “Consiglio Nazionale delle Ricerche” (C.N.R.) under Contract no. 115.4075.69.01220.
The suffixes “u” and “d” pertain to the conditions upstream and downstream of the screen with reference to the flow through it. The suffix “j” refers to the region “j” of the wave diagrams in Fig. 1. 相似文献
14.
This work experimentally visualizes the interaction of a quasi-one-dimensional moving shock wave with a two-dimensional vortex
in a soap film for the first time. A vertical soap film shock tube was used to generate a quasi-one-dimensional moving shock
wave and a NACA-0012 airfoil intruded into the soap film was towed to shed the starting vortex. The interesting interaction
phenomena were then visualized using a traditional high-speed flash photography. The concentration of sodium dodecyl sulfate
(SDS) used was 0.5 CMC (critical micelle concentration) to keep the surfactant molecules behave as two-dimensional gases.
A sequence of pictures shows that the shock is distorted non-symmetrically as it passes through the spiral vortex flow field
and the vortex structure is compressed in the direction normal to the shock. These flow features observed in soap films are
qualitatively similar to their counterparts in gases. In addition, the visualization of the interactions of a quasi-one-dimensional
moving shock wave with a Kármán vortex street are presented.
相似文献
15.
The apparent viscosities of purely viscous non-Newtonian fluids are shear rate dependent. At low shear rates, many of such
fluids exhibit Newtonian behaviour while at higher shear rates non-Newtonian, power law characteristics exist. Between these
two ranges, the fluid's viscous properties are neither Newtonian or power law. Utilizing an apparent viscosity constitutive
equation called the “Modified Power Law” which accounts for the above behavior, solutions have been obtained for forced convection
flows. A shear rate similarity parameter is identified which specifies both the shear rate range for a given fluid and set
of operating conditions and the appropriate solution for that range. The results of numerical solutions for the friction factor–Reynolds
number product and for the Nusselt number as a function of a dimensionless shear rate parameter have been presented for forced
fully developed laminer duct flows of different cross-sections with modified power law fluids. Experimental data is also presented
showing the suitability of the “Modified Power Law” constitutive equation to represent the apparent viscosity of various polymer
solutions.
Received on 21 August 2000 相似文献
16.
M. Sugawara E. Tamura Y. Satoh Y. Komatsu M. Tago H. Beer 《Heat and Mass Transfer》2007,43(10):1009-1018
Visual observations reveal a complicated flow in the liquid melt and a melting front configuration resulting from horizontal
ice plate melting from above into a 20 wt% calcium chloride aqueous solution. The initial temperature of the ice plate and
the mixture are both −5°C. Small scale “mountain and valley” structures (∼1 mm) appear on the flat melting front just after
melting begins, which have been called “sharkskin”. Innumerable upward and downward flows appear near the sharkskin and are controlled by its “mountain and valley” structure. These typical flows will considerably promote the melting of the
ice plate to be 30% larger as compared to the numerically predicted results assuming a flat melting front (i.e., without the
sharkskin), and also by three times larger compared with the results for melting from below. 相似文献
17.
The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until
now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic
microjets of 100–1,000 μm in size with exit velocities in the range of 300–500 m/s. Such microjets are presently being used
to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft,
cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally
investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with
a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger
supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained
using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets
operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects
associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that,
similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic
impinging jets. 相似文献
18.
A numerical method for two-phase flow with hydrodynamics behavior was considered. The nonconservative hyperbolic governing equations proposed by Saurel and Gallout were adopted. Dissipative effects were neglected but they could be included in the model without major difficulties. Based on the opinion proposed by Abgrall that “a two phase system, uniform in velocity and pressure at t = 0 will be uniform on the same variable during its temporal evolution“, a simple accurate and fully Eulerian numerical method was presented for the simulation of multiphase compressible flows in hydrodynamic regime. The numerical method relies on Godunov-typescheme, with HLLC and Lax-Friedrichs type approximate Riemann solvers for the resolution of conservation equations, and nonconservative equation. Speed relaxation and pressure relaxation processes were introduced to account for the interaction between the phases. Test problem was presented in one space dimension which illustrated that our scheme is accurate, stable and oscillation free. 相似文献
19.
The tomographic reconstruction of supersonic flows faces two challenges. Firstly, techniques used in the past, such as the
direct Fourier method (DFM) (Gottlieb and Gustafsson in On the direct Fourier method for computer tomography, 1998; Morton
in Tomographic imaging of supersonic flows, 1995) or various backprojection (Kak and Slaney in Principles of computerized
tomographic imaging, vol. 33 in Classics in Applied Mathematics, 2001) techniques, have only been able to reconstruct areas
of the flow which are upstream of any opaque objects, such as a model. Secondly, shock waves create sharp discontinuities
in flow properties, which can be difficult to reconstruct both in position and in magnitude with limited data. This paper
will present a reconstruction method, matrix inversion using ray-tracing and least squares conjugate gradient (MI-RLS), which uses geometric ray-tracing and a sparse matrix iterative solver (Paige and Saunders in ACM Trans. Math. Softw.
8(1):43–71, 1982) to overcome both of these challenges. It will be shown, through testing with a phantom object described
in tomographic literature, that the results compare favourably to those produced by the DFM technique. Finally, the method
will be used to reconstruct three-dimensional density fields from interferometric shock layer images, with good resolution
(Faletič in Tomographic reconstruction of shock layer flows, 2005).
This paper was based on work that was presented at the 3rd International Symposium on Interdisciplinary Shock Wave Research,
Canberra, Australia, March 1–3, 2006. 相似文献
20.
R. J. Exton R. J. Balla B. Shirinzadeh M. E. Hillard G. J. Brauckmann 《Experiments in fluids》1999,26(4):335-339
A new concept for flow visualization is demonstrated in which fluorescence from locally seeded iodine is viewed in the wake
of simple aerodynamic models at Mach 6. Localized seeding is performed by painting a small area of a ceramic model with a
tincture of iodine. When the model is injected into the flow, the adsorbed iodine is entrained into the boundary layer, follows
the model contour, and ultimately mixes into the wake region. Planar “snapshots” of the wake flow are taken by exciting the
iodine with an ArF excimer laser sheet at 193 nm and observing the fluorescence in the 210–600 nm region with an intensified
CCD camera.
Received: 17 July 1997/Accepted: 12 August 1998 相似文献