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1.
Mixing of jets is crucial for optimal performance of many industrial applications and there is a need to optimize both nozzle
geometry and flow conditions. The present study reports the influence of buoyancy and perforation on mixing between a jet
and its environment. Optical techniques are ideal for the study of jet mixing due to their non-intrusive and inertia free
properties. The present study gives an account of mixing between helium jet and the ambient fluid using a combination of color
schlieren deflectometry and radial tomographic mathematics. Four different perforation sizes have been used and the experiments
are performed for Reynolds numbers 21–676 and Richardson numbers 3.27–0.0015. Color schlieren images show distinct influence
of perforation and flow conditions (Richardson number). Oxygen concentration and jet width quantify effectiveness of jet mixing.
Buoyancy plays an important role in mixing at high Richardson number. Perforation improves jet mixing i.e. there is about
120% increase in jet width and the size of perforation plays an important role. 相似文献
2.
A method of theoretical investigation of the flow field in a two-dimensional (plane-parallel or axisymmetric) overexpanded
jet of an ideal perfect gas in the vicinity of the nozzle lip is described. The changes in curvature of the shock wave emanating
from the lip, as well as the shock-wave intensity and flow parameters behind the shock are analyzed as functions of the Mach
number, pressure ratio in the plane jet, and ratio of specific heats of the gas.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 3, pp. 72–83, May–June, 2006. 相似文献
3.
The injection of a liquid jet into a crossing Mach 6 air flow is investigated. Experiments were conducted on a sharp leading
edge flat plate with flush mounted injectors. Water jets were introduced through different nozzle shapes at relevant jet-to-air
momentum–flux ratios. Sufficient temporal resolution to capture small scale effects was obtained by high-speed recording,
while directional illumination allowed variation in field of view. Shock pattern and flow topology were visualized by Schlieren-technique.
Correlations are proposed on relating water jet penetration height and lateral extension with the injection ratio and orifice
diameter for circular injector jets. Penetration height and lateral extension are compared for different injector shapes at
relevant jet-to-air momentum–flux ratios showing that penetration height and lateral extension decrease and increase, respectively,
with injector’s aspect ratio. Probability density function analysis has shown that the mixing of the jet with the crossflow
is completed at a distance of x/d
j
~ 40, independent of the momentum–flux ratio. Mean velocity profiles related with the liquid jet have been extracted by means
of an ensemble correlation PIV algorithm. Finally, frequency analyses of the jet breakup and fluctuating shock pattern are
performed using a Fast Fourier algorithm and characteristic Strouhal numbers of St = 0.18 for the liquid jet breakup and of St = 0.011 for the separation shock fluctuation are obtained. 相似文献
4.
We investigate the gas-particle dynamics of a device designed for biological pre-clinical experiments. The device uses transonic/supersonic gas flow to accelerate microparticles such that they penetrate the outer skin layers. By using a shock tube coupled to a correctly expanded nozzle, a quasi-one-dimensional, quasi-steady flow (QSF) is produced to uniformly accelerate the microparticles. The system utilises a microparticle “cassette” (a diaphragm sealed container) that incorporates a jet mixing mechanism to stir the particles prior to diaphragm rupture. Pressure measurements reveal that a QSF exit period – suitable for uniformly accelerating microparticles – exists between 155 and 220 mus after diaphragm rupture. Immediately preceding the QSF period, a starting process secondary shock was shown to form with its (x,t) trajectory comparing well to theoretical estimates. To characterise the microparticle, flow particle image velocimetry experiments were conducted at the nozzle exit, using particle payloads with varying diameter (2.7–48 μm), density (600–16,800 kg/m3) and mass (0.25–10 mg). The resultant microparticle velocities were temporally uniform. The experiments also show that the starting process does not significantly influence the microparticle nozzle exit velocities. The velocity distribution across the nozzle exit was also uniform for the majority of microparticle types tested. For payload masses typically used in pre-clinical drug and vaccine applications (≤ 1 mg), it was demonstrated that payload scaling does not affect the microparticle exit velocities. These characteristics show that the microparticle exit conditions are well controlled and are in agreement with ideal theory. These features combined with an attention to the practical requirements of a pre-clinical system make the device suitable for investigating microparticle penetration into the skin for drug delivery. 相似文献
5.
Density field of supersonic separated flow past an afterbody nozzle using tomographic reconstruction of BOS data 总被引:1,自引:0,他引:1
The background oriented Schlieren (BOS) technique has been applied to determine the density field in an oblique shock-separated
turbulent boundary flow. Measurements were made for two cases, namely, with/without jet flow from the afterbody which is a
nozzle. In addition, oil flow and Schlieren visualizations were carried out—the results show certain upstream features of
interest including shock excursions. The mean density field from BOS is discussed along with results from conventional Schlieren
flow visualization. The data extracted from the mean density field obtained through BOS have been compared for the jet-off
and jet-on cases. The data obtained also show the mean density in the base region (jet-off case) to be about 50% of the freestream
density and match the isentropic values for the underexpanded jet at the exit. The study involving shock–boundary interaction,
movement of freestream shock over the afterbody in the presence of a jet plume provides understanding of flow physics in a
flow regime where whole field velocity measurements are extremely difficult. 相似文献
6.
G. M. Schneider J. D. Hooper A. R. Musgrove G. J. Nathan R. E. Luxton 《Experiments in fluids》1997,22(6):489-495
A novel fluid mixing device, described elsewhere, has been shown to have a dramatic effect on the combustion characteristics
of a fuel jet. The main features of the flow are the deflection of the jet between 30° and 60° from the nozzle axis and its
precession about that axis. Many of the factors governing the nozzle instabilities which drive the mixing in the external
field are imprecisely defined. It is the aim of the present paper to examine, in isolation from the nozzle instabilities,
the influence of precession on a deflected jet as it proceeds downstream from the nozzle exit. The fluid dynamically driven
phenomena within the nozzle which cause the precession are in the present investigation replaced by a mechanical rotation
of a nozzle from which is emerging a jet which is orientated at an angle from the nozzle axis. By this means the effect of
precession on the deflected jet can be investigated independently of the phenomena which cause the precession.
The experimental data reported here has been obtained from measurements made using a miniature, rapid response four-hole “Cobra”
pitot probe in the field of the precessing jet. Phase-averaged three dimensional velocity components identify the large scale
motions and overall flow patterns. The measured Reynolds stresses complement the velocity data and are found to be compatible
with the higher entrainment rates of the jet found in earlier investigations.
Received: 8 November 1995 / Accepted: 27 September 1996 相似文献
7.
A. I. Usmanov 《Fluid Dynamics》1998,33(3):351-354
The dependence of the flow coefficient of a gas jet ejected from an orifice/nozzle into a subsonic/transonic cross-flow on
the flow and the jet Mach numbers, the off-design ratio, the nozzle inclination angle, β, and other determining parameters
is considered. The physical nozzle flow pattern is constructed on the basis of experimental data obtained for 0.3< M∞<1.75 and β=60°, 90°, and 120°. The results of measuring the pressure upstream and downstream of the orifice and on the windward
and leeward orifice generators are presented. It is shown that the flow rate coefficient of a jet ejected into a cross-flow
may exceed that of a similar jet outflowing into a flooded space.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 65–70, May–June, 1998. 相似文献
8.
The present study describes an experimental work to investigate the effect of a nozzle exit reflector on a supersonic jet that is discharged from a convergent–divergent nozzle with a design Mach number of 2.0. An annular reflector is installed at the nozzle exit and its diameter is varied. A high-quality spark schlieren optical system is used to visualize detailed jet structures with and without the reflector. Impact pressure measurement using a pitot probe is also carried out to quantify the reflector’s effect on the supersonic jet which is in the range from an over-expanded to a moderately under-expanded state. The results obtained show that for over-expanded jets, the reflector substantially increases the jet spreading rate and reduces the supersonic length of the jet, compared with moderately under-expanded jets. The reflector’s effect appears more significant in imperfectly expanded jets that have strong shock cell structures, but is negligible in correctly expanded jet. 相似文献
9.
In this research the fluid dynamics characteristics of a stellar turbulent jet flow is studied numerically and the results
of three dimensional jet issued from a stellar nozzle are presented. A numerical method based on control volume approach with
collocated grid arrangement is employed. The turbulent stresses are approximated using k–ε and k–ω models with four different inlet conditions. The velocity field is presented and the rate of decay at jet centerline is noted.
Special attention is drawn on the influence of corner angle and number of wings on mixing in stellar cross section jets. Stellar
jets with three; four and five wings and 15–65° corner angles are studied. Also the effect of Reynolds number (based on hydraulic
diameter) as well as the inflow conditions on the evolution of the stellar jet is studied. The Numerical results show that
the jet entrains more with corner angle 65° and five wings number. The jet is close to a converged state for high Reynolds
numbers. Also the influence of the inflow conditions on the jet characteristics is so strong. 相似文献
10.
Supersonic flow separation in planar nozzles 总被引:3,自引:1,他引:2
We present experimental results on separation of supersonic flow inside a convergent–divergent (CD) nozzle. The study is motivated
by the occurrence of mixing enhancement outside CD nozzles operated at low pressure ratio. A novel apparatus allows investigation
of many nozzle geometries with large optical access and measurement of wall and centerline pressures. The nozzle area ratio
ranged from 1.0 to 1.6 and the pressure ratio ranged from 1.2 to 1.8. At the low end of these ranges, the shock is nearly
straight. As the area ratio and pressure ratio increase, the shock acquires two lambda feet. Towards the high end of the ranges,
one lambda foot is consistently larger than the other and flow separation occurs asymmetrically. Downstream of the shock,
flow accelerates to supersonic speed and then recompresses. The shock is unsteady, however, there is no evidence of resonant
tones. The separation shear layer on the side of the large lambda foot exhibits intense instability that grows into large
eddies near the nozzle exit. Time-resolved wall pressure measurements indicate that the shock oscillates in a piston-like
manner and most of the energy of the oscillations is at low frequency.
相似文献
11.
D. Middleton 《International Journal of Heat and Fluid Flow》1983,4(1):43-52
Because of practical application to jet pumps, ejectors, furnaces and similar devices, the turbulent discharge of a round jet into a coaxial duct and the mixing patterns in the various regions into which the flow may be divided, are of considerable interest. In this paper the mixing of an incompressible jet with a similar fluid in a cylindrical tube is considered up to the plane which marks the disappearance of potential flow. Under the assumption of similarity of velocity profile and with neglect of the wall boundary layer and nozzle wake, the continuity and momentum equations, in integral form, are solved for the velocities and mixing region radii at any given section. Prandtl's momentum transfer hypothesis may be used to determine the dependence of these on distance downstream. By examining the various flow regimes in detail this analysis is formally able to cover ratios of primary to secondary flow velocities of from one to infinity and, similarly, all ratios of duct to nozzle diameters, thereby extending earlier investigations. It also corrects work on similar basis in which inappropriate linearisations were made. The ‘exact’ results constitute a basis from which extension to include additional effects may be made. 相似文献
12.
13.
Mark Linne David Sedarsky Terrence Meyer James Gord Campbell Carter 《Experiments in fluids》2010,49(4):911-923
We have investigated liquid breakup mechanisms in the near nozzle region of a high-pressure effervescent atomizer using ballistic
imaging. This technique has revealed various breakup regimes depending upon total flow rate and the gas-to-liquid ratio (GLR).
At low total speeds, the jet does not exhibit the wide spread angle and rapid breakup for which effervescent sprays are known,
even at high GLR. Above a distinct threshold value for total flow rate, the jet passes through several recognizable flow regimes
depending on GLR and it does achieve the expected wide spread angle and rapid breakup. Intermediate GLR’s produce interesting
flow patterns that seem to be generated by surging at the nozzle exit, and this surging can probably be attributed to the
flow pattern just at the nozzle exit. Indeed, specific interior flows seem to generate the most rapid breakup and should be
investigated further. 相似文献
14.
The pattern of the flow in the vicinity of an annular system of jets exiting into a supersonic stream from orifices on a cylindrical
surface with a turbulent boundary layer is experimentally investigated Four typical flow regimes are recorded The effect of
the jet number and the nozzle-to-outer pressure ratio on the extent of the separation zone and its structure ahead of and
behind the jet system is determined
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 21–27, January–February,
1999. 相似文献
15.
The results of an experimental investigation on the effect of a vortex generator in the form of a mechanical tab placed at the nozzle exit on the evolution of jet and its decay are reported in this paper. Jets from a sonic nozzle with and without tabs operated at nozzle pressure ratios from 2 to 7 were studied. Tabs with two combinations of length-to-width ratio were investigated by keeping the blockage area constant. The tabs offered a blockage of 10.18% of the nozzle exit area. The centerline pitot pressure decay shows that for the tabbed jet a maximum core reduction of about 75% can be achieved at a nozzle pressure ratio (NPR) 7 compared to an uncontrolled jet. The shadowgraph pictures show that the tabs drastically weaken the shock structure in the jet core and disperse the supersonic zone of the flow making them occupy a greater zone of the flow field compared to the plain nozzle. This causes the waves to become weaker and the jet to spread faster. The tabs are found to shed counter-rotating vortices all along the edges, resulting in enhanced mixing. Isobaric contours reveal that the streamwise vortices cause an inward indentation of the entrained mass into the jet core and an outward ejection of core flow. To understand the distortion introduced by tabs on the jet cross-section and its growth leading to bifurcation of the jet, a surface coating visualization method was developed and employed. 相似文献
16.
Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: the influence of small aspect ratio 总被引:1,自引:0,他引:1
Ehsan Faghani Reza Maddahian Pedram Faghani Bijan Farhanieh 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(7):727-745
In this research, the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results
of three-dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach
with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent
stresses are approximated using k–e{\varepsilon} model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay
at the jet centerline are noted. The velocity vectors of the main flow and the secondary flow are illustrated. Also, effect
of aspect ratio on mixing in rectangular cross-section jets is considered. The aspect ratios that were considered for this
work were 1:1 to 1:4. The results showed that the jet entrains more with smaller AR. Special attention has been drawn to the
influence of the Reynolds number (based on hydraulic diameter) as well as the inflow conditions on the evolution of the rectangular
jet. An influence on the jet evolution is found for smaller Re, but the jet is close to a converged state for higher Reynolds numbers. The inflow conditions have considerable influence
on the jet characteristics. 相似文献
17.
Mixing of high speed coaxial jets 总被引:3,自引:0,他引:3
R. I. Sujith R. Ramesh S. Pradeep S. Sriram T. M. Muruganandam 《Experiments in fluids》2001,30(3):339-345
In this study, five different supersonic nozzles – conical, elliptical, tabbed, radially lobed and two-dimensional lobed
– are compared experimentally for their mixing performance. With the background of studies by various groups conducted on
the above nozzles, the present paper aims to provide an experimental comparison of their respective mixing performances with
that of a conventional conical nozzle under identical operating conditions. The mixing of the supersonic stream coming from
such nozzles with a coaxial sonic stream is investigated. The investigation is performed non-intrusively, using digital image
processing of planar Mie-scattering images of the flow field. The results of these investigations reveal the superiority of
mixing performance of the two-dimensional lobed nozzle over conventional circular and other non-conventional nozzles.
Received: 15 July 1999/Accepted: 3 July 2000 相似文献
18.
We establish the existence and stability of multidimensional steady transonic flows with transonic shocks through an infinite
nozzle of arbitrary cross-sections, including a slowly varying de Laval nozzle. The transonic flow is governed by the inviscid
potential flow equation with supersonic upstream flow at the entrance, uniform subsonic downstream flow at the exit at infinity,
and the slip boundary condition on the nozzle boundary. Our results indicate that, if the supersonic upstream flow at the
entrance is sufficiently close to a uniform flow, there exists a solution that consists of a C
1,α subsonic flow in the unbounded downstream region, converging to a uniform velocity state at infinity, and a C
1,α multidimensional transonic shock separating the subsonic flow from the supersonic upstream flow; the uniform velocity state
at the exit at infinity in the downstream direction is uniquely determined by the supersonic upstream flow; and the shock
is orthogonal to the nozzle boundary at every point of their intersection. In order to construct such a transonic flow, we
reformulate the multidimensional transonic nozzle problem into a free boundary problem for the subsonic phase, in which the
equation is elliptic and the free boundary is a transonic shock. The free boundary conditions are determined by the Rankine–Hugoniot
conditions along the shock. We further develop a nonlinear iteration approach and employ its advantages to deal with such
a free boundary problem in the unbounded domain. We also prove that the transonic flow with a transonic shock is unique and
stable with respect to the nozzle boundary and the smooth supersonic upstream flow at the entrance. 相似文献
19.
The 3-D density field of a round, neutrally buoyant turbulent jet is obtained using a finite-fringe, shearing interferometer.
A He–Ne laser beam (λ=632.8 nm) is subdivided into six beams of equal intensity, which intersect a helium–argon jet flowing
from a vertical nozzle. Two-dimensional projection data of the jet are captured simultaneously from six viewing directions
distributed over 140°. The desired phase is removed from the spatial carrier using the Fourier transform method. A tomographic
reconstruction technique, using a truncated Fourier–Bessel expansion is performed to obtain the complete 3-D density field.
The Reynolds number, based on the exit mean velocity and the nozzle diameter, is 5890.
Received: 22 December 1999/Accepted: 20 January 2000 相似文献
20.
Oscillatory flows of a choked underexpanded supersonic impinging jet issuing from a convergent nozzle have been computed using
the axisymmetric unsteady Navier--Stokes system. This paper focuses on the oscillatory flow features associated with the variation
of the nozzle-to-plate distance and nozzle pressure ratio. Frequencies of the surface pressure oscillation and flow structural
changes from computational results have been analyzed. Staging behavior of the oscillation frequency has been observed for
both cases of nozzle-to-plate distance variation and pressure ratio variation. However, the staging behavior for each case
exhibits different features. These two distinct staging behaviors of the oscillation frequency are found to correlate well
if the frequency and the distance are normalized by the length of the shock cell. It is further found that the staging behavior
is strongly correlated with the change of the pressure wave pattern in the jet shear layer, but not with the shock cell structure.
Communicated by K. Takayama
PACS 02.60.Cb; 47.40.−x; 47.40.Nm; 47.35.+I; 47.15.−x 相似文献