共查询到20条相似文献,搜索用时 664 毫秒
1.
In this study four different supersonic nozzles – circular, elliptical, tabbed, and radially lobed nozzles are compared experimentally
for their freejet mixing performance. With the background of studies by various groups conducted on elliptical, tabbed, and
radially lobed nozzles, the present paper aims at a comparative experimental study to compare their mixing performance with
that of a conventional circular nozzle under identical operating conditions. The investigation is performed non-intrusively,
using digital image processing of the planar Mie scattering images of the flow field. The results of these investigations
reveal the superiority of the mixing performance of the lobed nozzles over conventional circular and other non-conventional
nozzles.
Received: 29 July 1998/Accepted: 5 November 1999 相似文献
2.
Studies on mixing enhancement with two dimensional (2D) lobed nozzle have been conducted in a dual stream supersonic flow
facility. The distributions of momentum flux, stagnation pressure and stagnation temperature across a plane at different axial
distances from the nozzle exit were considered as a measure of mixing. The results indicated an enormous enhancement in mixing
when 2D lobed nozzle was employed in comparison with conventional plain 2D nozzle. The enhanced mixing performance could be
attributed to the large scale axial vortices observed in the flow-field of subsonic lobed nozzles by earlier investigators.
Received: 27 December 1996 / Accepted: 21 August 1997 相似文献
3.
The freejet characteristics of radially lobed nozzles were studied experimentally. Schlieren photographs of the freejets revealed that the lobes of the nozzles gave rise to alternate expansion-compression regions. For two of the lobed nozzles the potential core was reduced by a factor of three relative to the conical nozzle tested. The jet spread and the shear layer thickness of the lobed nozzles were considerably higher than those for the conical nozzle. The jet width and the shear layer thickness were higher in the major plane; however, the shear layer growth rate was higher in the minor plane of the lobed nozzles. Jet axial thrust measurements revealed a thrust loss of 14% for two of the lobed nozzles tested. 相似文献
4.
Vortex dynamics and mass entrainment in turbulent lobed jets with and without lobe deflection angles 总被引:2,自引:0,他引:2
Passive control of jet flows in order to enhance mixing and entrainment is of wide applicative interest. Our purpose is to
develop new air diffusers for HVAC systems, by using lobed geometry nozzles, in order to ameliorate users the thermal comfort.
Two turbulent 6-lobed air jets with and without lobe deflection angles were studied experimentally and compared with a reference
circular jet having the same initial Reynolds number. The main objective was to analyze the modifications occurring in the
vortex dynamics of the flow, firstly by replacing a circular tube with a straight lobed tube, and secondly by a lobed tube
having a double inclination of the lobes. Rapid visualizations of the flows and hot-wire measurements of the streamwise velocity
spectra allow understanding the vortex roll-up mechanisms. Unlike the circular jet, where the primary rings are continuous,
the Kelvin–Helmholtz vortices in the lobed jet flows were found to be discontinuous. The resulting “ring segments” detach
at different frequencies whether they are shed in the lobe troughs or at the lobe sides. One explanation relies on the strong
variation of the exit plane curvature. Additionally, a speculative scenario of the vortical dynamics is advanced by the authors.
The discontinuous nature of the K–H vortices enables the development of secondary streamwise structures, non-influenced by
the passage of the primary structures as in the case of the circular jet. Thus, the momentum flux transport role played by
the streamwise structures is rendered more efficient and leads to a spectacular increase in the entrainment rate in the initial
region. The amount of fluid being entrained in the lobed jet by the streamwise structures is drastically amplified by the
double inclination of the nozzle exit boundary. 相似文献
5.
Within the framework of the ideal, i.e., inviscid and non-heat conducting, gas model we consider the problem of designing
the supersonic section of a two-dimensional or axisymmetric nozzle realizing a uniform supersonic flow limitingly similar
with a sonic flow when the choked flow involves a curvilinear sonic line. Emphasis is placed on nozzles with abruptly or steeply
converging subsonic sections and a strongly curved sonic line formed by the C
−-characteristics of the expansion fan with the focus at the lower bend point of the vertical section of the subsonic contour.
In the two-dimensional case, the least possible greater-than-unity Mach number M
em at the nozzle exit corresponds to the flow in which the first intersection of the C
+-characteristics originated at the closing C
−-characteristic of the expansion fan falls on the unknown contour of its supersonic part. For a uniform flow with M
e
< M
em the intersection of C
+-characteristics beneath the unknown contour make impossible its construction. A part of the contour realizing a uniform flow
with M
em > 1 ensures a limitingly rapid flow acceleration and forms the initial region of the supersonic generator of a maximum-thrust
nozzle. For this reason, in the case of a curvilinear sonic line the supersonic generators of these nozzles have two, rather
than one, bends, which, however, is interesting only for the theory. At least, in the calculated examples the thrusts of the
nozzles with one and two bends differ only by a hundredth or even thousandth fractions of per cent. 相似文献
6.
Thrust shock vector control of an axisymmetric conical supersonic nozzle via secondary transverse gas injection 总被引:1,自引:0,他引:1
Transverse secondary gas injection into the supersonic flow of an axisymmetric convergent–divergent nozzle is investigated to describe the effects of the fluidic thrust vectoring within the framework of a small satellite launcher. Cold-flow dry-air experiments are performed in a supersonic wind tunnel using two identical supersonic conical nozzles with the different transverse injection port positions. The complex three-dimensional flow field generated by the supersonic cross-flows in these test nozzles was examined. Valuable experimental data were confronted and compared with the results obtained from the numerical simulations. Different nozzle models are numerically simulated under experimental conditions and then further investigated to determine which parameters significantly affect thrust vectoring. Effects which characterize the nozzle and thrust vectoring performances are established. The results indicate that with moderate secondary to primary mass flow rate ratios, ranging around 5 %, it is possible to achieve pertinent vector side forces. It is also revealed that injector positioning and geometry have a strong effect on the shock vector control system and nozzle performances. 相似文献
7.
F. I. Lukhtura 《Fluid Dynamics》1994,29(4):585-588
The possibility of critical gas flow from Laval nozzles in overexpanded regimes behind a bridge shock is investigated theoretically
with and without allowance for viscous mixing at the edge of the jet. The influence of the mixing effect and flow separation
from the nozzle walls on the critical flow conditions is analyzed. It is shown experimentally that these regimes coincide
closely with the displacement of the normal shock to the nozzle exit and cessation of the emission by the jet of a discrete
tone.
Mariupol. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 180–184, July–August,
1994. 相似文献
8.
This paper describes the dynamic characteristics of pulsed, supersonic liquid fuel sprays or jets injected into ambient air.
Simple, single hole nozzles were employed with the nozzle sac geometries being varied. Different fuel types, diesel fuel,
bio-diesel, kerosene, and gasoline were used to determine the effects of fuel properties on the spray characteristics. A vertical
two-stage light gas gun was employed as a projectile launcher to provide a high velocity impact to produce the liquid jet.
The injection pressure was around 0.88–1.24 GPa in all cases. The pulsed, supersonic fuel sprays were visualized by using
a high-speed video camera and shadowgraph method. The spray tip penetration and velocity attenuation and other characteristics
were examined and are described here. An instantaneous spray tip velocity of 1,542 m/s (Mach number 4.52) was obtained. However,
this spray tip velocity can be sustained for only a very short period (a few microseconds). It then attenuates very quickly.
The phenomenon of multiple high frequency spray pulses generated by a single shot impact and the changed in the angle of the
shock structure during the spray flight, which had already been observed in previous studies, is again noted. Multiple shock
waves from the conical nozzle spray were also clearly captured.
相似文献
9.
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
10.
Aerodynamic experimentation with ducted models as applied to hypersonic air-breathing vehicles 总被引:1,自引:0,他引:1
Yu. P. Goon’ko 《Experiments in fluids》1999,27(3):219-234
A methodology of experimentation in high supersonic wind tunnels for studying aerodynamic characteristics of hypersonic flying
vehicles powered by air-breathing engines is discussed. Investigations of such total aerodynamic forces as drag, lift and
pitching moment at testing the models are implicit when the air flow through the model ducts is accomplished so that to provide
the simulation of the external flow around the airplane and flow over the inlets, but the operating engines and, hence, the
exhaust jets are not modeled. The methods used for testing such models are based on the measurement of duct stream parameters
alongside with the balance measurement of aerodynamic forces acting on the models. In the tests, aerometric tools are used
such as narrow metering nozzles (plugs), pitot and static pressure probes, stagnation temperature probes and pressure orifices
in walls of the model duct. The aerometric data serve to determine the flow rate and momentum of the stream at the duct exit.
The internal non-simulated forces of the model ducts are also determined using the conservation equations for energy, mass
flow and momentum, and these forces are eliminated from the aerodynamic test results. The techniques of the said model testing
have been well developed as applied to supersonic aircraft, however their application for hypersonic vehicles whose models
are tested at high supersonic speeds, Mach number M
∞>4, implies some specific features. In the present paper, the results of experimental and theoretical study of these features
are discussed. Some experimental data on aerodynamics of hypersonic aircraft models received in methodological tests are also
presented. The tunnel experiments have been carried out in the Mach number range M
∞=2–6.
Received: 25 July 1996/ Accepted: 14 December 1998 相似文献
11.
In connection with the use of supersonic nozzles to create lasers, the question arises of the optimum parameters of the nozzle and the gas mixture from the aspect of obtaining the greatest population inversion of the energy levels of internal degrees of freedom of molecules of the working gas and the greatest output power of the lasers. A rather complete concept of the kinetic processes taking place during the escape of a relaxing gas mixture containing carbon dioxide through a supersonic nozzle has now been developed on the basis of calculated and experimental data. In [1–4] the problems of optimization of the parameters of a CO2-N2-H2O-He mixture and of the shape of the nozzle were set up and solved in a one-dimensional steady-state formulation. The influence of the two-dimensionality of the stream in an optimum nozzle on the laser characteristics is studied in the present report. The method of through calculation suggested in [5] is used to calculate the two-dimensional flow of a relaxing gas.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 23–26, September–October, 1978. 相似文献
12.
I. L. Pankrat'eva V. A. Polyanskii V. I. Sakharov 《Journal of Applied Mechanics and Technical Physics》1998,39(6):908-914
The operation of a source of charged aerosol particles which consists of a supersonic nozzle, a corona-forming needle-shaped
electrode, and a device for injecting liquid droplets into a gas flow is considered. A theoretical model for two-dimensional,
two-phase flow in the nozzle is considered. An algorithm of numerical calculation of such a flow is developed, and results
of calculations of the electric transport current from the nozzle are given.
Institute of Mechanics, Moscow State University, Moscow 117192. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika,
Vol. 39, No. 6, pp. 102–109, November–December, 1998. 相似文献
13.
S. P. Kiselev V. P. Kiselev V. N. Zaikovskii 《Journal of Applied Mechanics and Technical Physics》2017,58(6):1021-1032
Results of experimental investigations and numerical simulations of supersonic gas flows in radial nozzles with different nozzle widths are presented. It is demonstrated that different types of the flow are formed in the nozzle with a fixed nozzle radius and different nozzle widths: supersonic flows with oblique shock waves inducing boundary layer separation are formed in wide nozzles, and flows with a normal pseudoshock separating the supersonic and subsonic flow domains are formed in narrow nozzles (micronozzles). The pseudoshock structure is studied, and the total pressure loss in the case of the gas flow in a micronozzle is determined. 相似文献
14.
Investigations of gas and particle dynamics in first generation needle-free drug delivery devices 总被引:1,自引:0,他引:1
Abstract. Transdermal powdered drug delivery involves the propulsion of solid drug particles into the skin by means of high-speed gas-particle
flow. The fluid dynamics of this technology have been investigated in devices consisting of a convergent-divergent nozzle
located downstream of a bursting membrane, which serves both to initiate gas flow (functioning as the diaphragm of a shock
tube) and to retain the drug particles before actuation. Pressure surveys of flow in devices with contoured nozzles of relatively
low exit-to-throat area ratio and a conical nozzle of higher area ratio have indicated a starting process of approximately
200 s typical duration, followed by a quasi-steady supersonic flow. The velocity of drug particles exiting the contoured nozzles
was measured at up to 1050 m/s, indicating that particle acceleration took place primarily in the quasi-steady flow. In the
conical nozzle, which had larger exit area ratio, the quasi-steady nozzle flow was found to be overexpanded, resulting in
a shock system within the nozzle. Particles were typically delivered by these nozzles at 400 m/s, suggesting that the starting
process and the quasi-steady shock processed flow are both responsible for acceleration of the particle payload. The larger
exit area of the conical nozzle tested enables drug delivery over a larger target disc, which may be advantageous.
Received 12 March 2000 / Accepted 8 June 2000 相似文献
15.
High order numerical simulation of the thermal load on a lobed strut injector for scramjet applications 下载免费PDF全文
In this paper, the thermal load on an actively cooled lobed strut injector for scramjet (supersonic combustion ramjet) applications is investigated numerically. This requires coupled simulations of the strut internal and external flow fields together with the heat conduction in the solid injector body. In order to achieve a fast mixing, the lobed strut is positioned at the channel axis to inject hydrogen into the core of a Mach 3 air stream. There it is exposed to the extremely high temperatures of the high speed flow. While the external air and hydrogen flows are supersonic, the strut internal hydrogen flow is mainly subsonic, in some regions at very low Mach numbers. To enable a simulation of the internal flow field which ranges from very low to very high Mach numbers (approximately Mach 2.25 at the nozzle exit), a preconditioning technique is employed. The compressible finite‐volume scheme uses a spatially fourth order multi‐dimensional limiting process discretization, which is used here for a first time to simulate a geometrically and fluid mechanically highly complex problem. It will be demonstrated that besides its high accuracy the multi‐dimensional limiting process scheme is numerically stable even in case of demanding practical applications. The coupled simulation of the lobed strut injector delivers unique insight into the flow phenomena inside and outside the strut, the heat fluxes, the temperature distribution in the solid material, the required hydrogen mass flux with respect to cooling requirements and details concerning the conditions at the exit of the injector. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
The article gives the results of an experimental investigation of the emission of a discrete tone by supersonic jets flowing out of conical supersonic nozzles. It is shown that a change in the aperture angle of the nozzle, the other parameters remaining unchanged, has a considerable effect on the structure of the flow in the initial section of the jet, which leads to a change in the frequency of the discrete tone and in the range of the degree of the rated capacity with which it arises. 相似文献
17.
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
18.
Yu. V. Tunik 《Fluid Dynamics》2010,45(2):264-270
The flow of igniting hydrogen-air mixtures entering an axisymmetric convergent-divergent nozzle at a supersonic velocity is
considered. A possibility of stabilizing detonation combustion is numerically investigated at different freestream Mach numbers
with account for nonuniform distribution of hydrogen concentration at the nozzle entry. The investigation is performed on
the basis of the two-dimensional gasdynamic Euler equations for a multicomponent reacting gas. A detailed model of chemical
reactions is used. The calculated thrust is compared with the drag of a conical housing containing the supersonic nozzle considered. 相似文献
19.
The variational problem of determining the optimal contour of an outlet system consisting of the supersonic jet-engine nozzle
and the tail of the flight vehicle is solved by the direct method. Some optimal contours of two-dimensional outlet systems
are calculated taking the effects of the external flow, the base, the angle of attack, and certain other factors into account.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 169–178, January–February,
1998. 相似文献
20.
A. V. Lokotko 《Journal of Applied Mechanics and Technical Physics》1999,40(6):1061-1069
A method of experimental determination of the force characteristics of nozzles (thrust, lift, and pitching moment) simultaneously
with the aerodynamic characteristics of an aircraft model in a supersonic flow in proposed. The tests were conducted for a
special methodical model, with equilibrium of the thrust and drag jorces being reached. It is shown that the internal force
characteristics of the nozzle and the drag of the model, as well as the effective lift and pitching moment (with account of
propulsion), can be determined from the measured thrust of the propulsion simulator.
Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 73–82, November–December, 1999. 相似文献