共查询到20条相似文献,搜索用时 156 毫秒
1.
A. P. Alkhimov V. F. Kosarev A. N. Papyrin 《Journal of Applied Mechanics and Technical Physics》1998,39(2):318-323
We present results of an experimental study of the specific features of the gas-dynamic formation of coatings from metallic
powders (dp<50 μm) on substrates of various materials depending on the particle velocity (200–1200m/sec), the jet temperature (300–700K), and other parameters. Results of a prospecting study of the implementation of the methods of particle acceleration in supersonic
(M=2.0–3.0) rectangular nozzles are described. The rate of bond formation in a cold particle-cold substrate contact occurring
in gas-dynamic spraying is estimated within the framework of the concepts applied in analysis of gas-dynamic spraying.
Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated
from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 2, pp. 182–188, March–Apil, 1998. 相似文献
2.
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
3.
Statistical Properties of Turbulent Free Jets Issuing from Nine Differently-Shaped Nozzles 总被引:1,自引:0,他引:1
This paper reports the centerline evolutions of turbulent statistical properties in nine air jets issuing from differently-shaped
nozzles into still air surroundings. All nozzles of investigation have nominally identical opening areas or equal equivalent
diameters (D
e
) and their aspect ratio (AR) varies from AR = 1 (circle) to AR = 2.5 (isosceles triangle). Present measurements were made at the Reynolds number (based on D
e
) of approximately 15,000. Results show that the loss of jet-axisymmetry at the exit generally causes the mean velocity decaying
faster, and the fluctuating intensity growing, in the near field, thus indicating the increased overall entrainment rate.
It is also shown that a change of shape of the nozzle exit does not affect the asymptotic decay rate of the centreline velocity
in the far field. The near-field structure of the isosceles-triangular jet is deduced to be most three-dimensional, compared
with the circular counterpart from smooth contraction being least. These discrepancies, however, weaken as the downstream
distance x is increased. Beyond x/D
e
= 20–30, the normalized velocity spectra for all jets of small AR collapse well, indicating similar statistical behaviors over a wide range of scales in the central region. Indeed, sufficiently
downstream from the exit, insignificant differences occur in jets’ velocity probability density function (PDF), the related
skewness and flatness factors, and also in their Taylor and Kolmogorov microscales. It is demonstrated that all the length
scales grow approximately linearly with x at x/D
e
≥ 20. 相似文献
4.
Edward T. Kopesky Stephen G. Boyes Neil Treat Robert E. Cohen Gareth H. McKinley 《Rheologica Acta》2006,45(6):971-981
Two distinct oligomeric species of similar mass and chemical functionality (M
w≈2,000 g/mol), one a linear methyl methacrylate oligomer (radius of gyration R
g≈1.1 nm) and the other a hybrid organic–inorganic polyhedral silsesquioxane nanocage (methacryl-POSS, r≈1.0 nm), were subjected to thermal and rheological tests to compare the behaviors of these geometrically dissimilar molecules over the entire composition range. The glass transition temperatures of the blends varied monotonically between the glass transition temperatures of the pure oligomer (T
g=−47.3°C) and the pure POSS (T
g=−61.0°C). Blends containing high POSS contents (with volume fraction φ
POSS≥0.90) exhibited enhanced enthalpy relaxation in differential scanning calorimetry (DSC) measurements, and the degree of enthalpy relaxation was used to calculate the kinetic fragility indices m of the oligomeric MMA (m=59) and the POSS (m=74). The temperature dependences of the viscosities were fitted by the free-volume based Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) framework and a dynamic scaling relation. The calculated values of the fragility from the WLF–VFT fits were similar for the POSS (m=82) and for the oligomer (m=76), and the dynamic scaling exponent was similar for the oligomeric MMA and the POSS. Within the range of known fragilities for glass-forming liquids, the temperature dependence of the viscosity was found to be similarly fragile for the two species. The difference in shape of the nanocages and oligomer chains is unimportant in controlling the glass-forming properties of the blends at low volume fractions (φ
POSS<0.20). However, at higher volume fractions, adjacent POSS cages begin to crowd each other, leading to an increase in the fractional free volume at the glass transition temperature and the observed enhanced enthalpy relaxation in DSC. 相似文献
5.
This article employs LES to simulate temporal mixing layers with Mach numbers ranging from M
c
= 0.3 to M
c
= 1.2. A form of approximate deconvolution together with a dynamic Smagorinsky subgrid model are employed as subgrid models.
A large computational domain is used along with relatively good resolution. The LES results regarding growth rate, turbulence
levels, turbulence anisotropy, and pressure–strain correlation show excellent agreement with those available from previous
experimental and DNS results of the same flow configuration, underlining the effectiveness and accuracy of properly conducted
LES. Coherent structures during the transitional stage change from spanwise aligned rollers to streamwise-aligned thinner
vortices at high Mach number. In the quasi-self-similar turbulent stage, the resolved-scale vorticity is more isotropic at
higher M
c
, and its vertical correlation length scale is smaller. The ratio of the vertical integral length scale of streamwise velocity
fluctuation to a characteristic isotropic estimate is found to decrease with increasing M
c
. Thus, compressibility leads to increased spatial decorrelation of turbulence which is one reason for the reduction in pressure–strain
correlation with increasing M
c
. The balance of the resolved-scale fluctuating vorticity is examined, and it is observed that the linear production by mean
shear becomes less important compared to nonlinear vortex stretching at high M
c
. A spectral decomposition of the pressure fluctuations into low- and intermediate-to-high-wave numbers is performed. The
low-wave number part of the pressure field is found not to correlate with the strain field, although it does have a significant
contribution to the r.m.s of the fluctuating pressure. As a consequence, the pressure–strain correlation can be analyzed using
a simplified Green’s function for the Poisson equation as is demonstrated here using the LES data. 相似文献
6.
S. V. Yagudin 《Fluid Dynamics》2012,47(2):214-222
Inviscid gas flows in nozzles with a uniform exit flow and contours profiled starting from the lower point of a steeply converging
region with an angle θ = −90° are analyzed. It is shown that there exists a class of convergent-divergent contours, within which the flow is characterized
by the fact that the line θ = 0 of zero angle of the velocity vector inclination to the x axis consists of two oppositely-directed regions located partially or even completely ahead of the minimum section, while
near the minimum sections their regions convex inward the gas stream are in decelerated flow. The minimum sections of the
nozzles with M
e
→ 1 approach the center of the nozzle from the right. 相似文献
7.
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
8.
A. A. Vasil’ev V. N. Rychkov M. E. Topchiyan 《Journal of Applied Mechanics and Technical Physics》2007,48(3):361-367
The laminar-turbulent transition is experimentally studied in boundary-layer flows on cones with a rectangular axisymmetric
step in the base part of the cone and without the step. The experiments are performed in an A-1 two-step piston-driven gas-dynamic
facility with adiabatic compression of the working gas with Mach numbers at the nozzle exit M
∞ = 12–14 and pressures in the settling chamber P0 = 60–600 MPa. These values of parameters allow obtaining Reynolds numbers per meter near the cone surface equal to Re
1e = (53–200) · 106
m
−1. The transition occurs at Reynolds numbers Re
tr
= (2.3–5.7) · 106.
__________
Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 3, pp. 76–83, May–June, 2007. 相似文献
9.
Schweizer et al. [J Rheol 48(6):1345–1363, 2004] showed nonlinear step shear rate data for a polystyrene melt (M
w=200 kg/mol, M
w/M
n=1.06, T=175°C). For different rheometers, cone angles, and sample sizes, the delayed normal force rise observed therein relative to a compliance-free reference N
1 (from a thermodynamically consistent reptation model) is shown to depend on rheometer compliance characterized by the instrument stiffness K
A. K
A can be obtained from mapping N
1 on the measured N
1,meas. or directly from mechanical contact measurement with a mismatch of 20–30%. The ranking of the stiffnesses found is K
A(RMS 800)>K
A(MCR 300)>K
A(ARES LR2). Once K
A is known, N
1,meas.-data can be corrected by solving the ill-posed Volterra equation involved in it. The correction shown for experiments with the 0.15-rad cone angle gives very good results. The characteristic decay time of the normal force after cessation of flow scales linearly with the axial response time t
a calculated from K
A, cone angle, and sample radius. The torque decay time is practically independent of t
a.Extended Version of a paper presented at the 2nd Annual European Rheology Conference in Grenoble, France, April 21–25, 2005. 相似文献
10.
The imbedded-fiber retraction (IFR) method was used to study the effect of temperature and PDMS molecular weight on the interfacial
tension of PS/PDMS blends. The interfacial tension decreased with increasing temperature and analysis of the temperature dependence
using a simple linear fit gave –dγ/dT value of 0.058±0.010 dyn/cm-deg. Reported –dγ/dT values of PS/PDMS blends are highly
dependent on the molecular weights of the polymers and can have values that are <0, 0, or >0. Our interfacial tension values
were independent of the molecular weight of PDMS and this was attributed to the molecular weights studied here being well
above the entanglement values of both polymers. However, analysis of interfacial tension data from this work and the literature
showed the following empirical relationship between apparent blend molecular weight, Mb, and interfacial tension of PS/PDMS blends with a correlation of 0.94: γ12=γ0+k2Mb
(–2/3), where γ0=7.3±0.3 dyn/cm; k2=–517±41 (dyn/cm)(g/mol)2/3. 相似文献
11.
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
12.
Henning Storz Ulrich Zimmermann Heiko Zimmermann Werner-Michael Kulicke 《Rheologica Acta》2010,49(2):155-167
Ultra-high viscosity alginates were extracted from the brown seaweeds Lessonia nigrescens (UHVN, containing 61% mannuronate (M) and 2% guluronate (G)) and Lessonia trabeculata (UHVT, containing 22% M and 78% G). The viscoelastic behavior of the aqueous solutions of these alginates was determined in shear
flow in terms of the shear stress σ
21, the first normal stress difference N
1, and the shear viscosity η in isotonic NaCl solutions (0.154 mol/L) at T = 298 K in dependence of the shear rate [(g)\dot]\dot{\gamma} for solutions of varying concentrations and molar masses (3–10 × 105 g/mol, homologous series was prepared by ultrasonic degradation). Data obtained in small-amplitude oscillatory shear (SAOS)
experiments obey the Cox–Merz rule. For comparison, a commercial alginate with intermediate chemical composition was additionally
characterized. Particulate substances which are omnipresent in most alginates influenced the determination of the material
functions at low shear rates. We have calculated structure–property relationships for the prediction of the viscosity yield,
e.g., η–M
w–c–[(g)\dot]\dot{\gamma} for the Newtonian and non-Newtonian region. For the highest molar masses and concentrations, the elasticity yield in terms
of N
1 could be determined. In addition, the extensional flow behavior of the alginates was measured using capillary breakup extensional
rheometry. The results demonstrate that even samples with the same average molar mass but different molar mass distributions
can be differentiated in contrast to shear flow or SAOS experiments. 相似文献
13.
Results of the experimental studies of the commutation characteristics of an electroexplosive breaker upon heating of a copper
foil by a current pulse of duration τ≈1msec are given. The dependences of the electric-field strength and the specific power of the circuit breaker during an electroexplosion
of the foil on the specific power of the source Ps are found and it is shown that the transition of the plasma-free regime of electroexplosion of the foil to a plasma regime
occurs for Ps=30–40GW/g.
Institute of Experimental Physics, Sarov 607190. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41, No.
1, pp. 14–20, January–February, 2000. 相似文献
14.
The stress dependencies of the steady-state viscosity η and, particularly, that of the steady-state elastic compliance J
e of various linear isotactic polypropylenes (PP) and one long-chain branched PP are investigated using creep-recovery tests.
The creep stresses applied range from 2 to 10,000 Pa. In order to discuss the stress-dependent viscosity η and elastic compliance J
e with respect to the influence of the weight average molar mass M
w and the polydispersity factor M
w/M
n the PP are characterized by SEC–MALLS. For the linear PP, linear steady-state elastic compliances Je0J_{\rm e}^0 in the range of 10 − 5–10 − 3 Pa − 1 are obtained depending on the molar mass distribution. Je0J_{\rm e}^0 of the LCB-PP is distinctly higher and comes to lie at around 10 − 2 Pa − 1. Je0J_{\rm e}^0 is found to be independent of M
w but strongly dependent on polydispersity. η and J
e decrease with increasing stress. For the linear PP, J
e as a function of the stress τ is temperature independent. The higher M
w/M
n the stronger is the shear thinning of η and the more pronounced is the stress dependence of J
e. For the LCB-PP, the strongest stress dependence of η and J
e is observed. Furthermore, for all PP J
e reacts more sensitively to an increasing stress than η. A qualitative explanation for the stronger stress dependence of J
e compared to η is given by analyzing the contribution of long relaxation times to the viscosity and elasticity. 相似文献
15.
Thomas Schweizer 《Rheologica Acta》2007,46(5):629-637
Creep experiments with a solution of polystyrene (M
w = 2.6 MDa, 16 vol.%, 25 °C) in diethyl phthalate are reported for stresses between 100 and 2,500 Pa (≈ 3G
N
0/4). The aim was to look for a flow transition as reported for strongly entangled poly(isobutylene) solutions. The experiments
with the polystyrene solution were repeated for cone angles of 2, 4, and 6° (radius 15 mm) and showed no dependence on cone
angle. The Cox–Merz rule was not fulfilled for stresses beyond about 800 Pa. The tangential observation with a CCD camera
showed that the edge took a concave shape because of the second normal stress difference. Beyond 1,000 Pa, the concave edge
develops into a crevice, thus substantially reducing the effective cross-section. This leads to runaway in a constant torque
experiment. At p
21 = 800 Pa, head-on particle tracking confirms that the originally linear velocity profile takes a gooseneck shape, thus revealing
shear banding. When the creep stress is stepped down to 100 Pa, this velocity profile evolves back to a linear one. The conclusion
from this work is that even if nonlinear creep experiments are reproducible and a steady state is reached, this does not mean
that the flow field is homogeneous.
This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006. 相似文献
16.
S.A. Triantafillou D.W. Schwendeman J.D. Cole 《Theoretical and Computational Fluid Dynamics》1998,12(4):219-232
A method of calculation is presented to determine conical wing shapes that minimize the coefficient of (wave) drag, C
D, for a fixed coefficient of lift, C
L, in steady, hypersonic flow. An optimization problem is considered for the compressive flow underneath wings at a small angle
of attack δ and at a high free-stream Mach number M
∞ so that hypersonic small-disturbance (HSD) theory applies. A figure of merit, F=C
D/C
L
3/2, is computed for each wing using a finite volume discretization of the HSD equations. A set of design variables that determine
the shape of the wing is defined and adjusted iteratively to find a shape that minimizes F for a given value of the hypersonic similarity parameter, H= (M
∞δ)−2, and planform area. Wings with both attached and detached bow shocks are considered. Optimal wings are found for flat delta
wings and for a family of caret wings. In the flat-wing case, the optima have detached bow shocks while in the caret-wing
case, the optimum has an attached bow shock. An improved drag-to-lift performance is found using the optimization procedure
for curved wing shapes. Several optimal designs are found, all with attached bow shocks. Numerical experiments are performed
and suggest that these optima are unique.
Received 1 May 1998 and accepted 14 October 1998 相似文献
17.
A. Klaczak 《Heat and Mass Transfer》2001,37(4-5):443-448
This article presents the results of laboratory research on heat exchange while heating water in horizontal and vertical
tubes with twisted-tape inserts.
The scope of the research:
70 ≤ Re ≤ 4000
3.6 ≤ Pr ≤ 5.9
8.6 ≤ Gz ≤ 540
The research was held for three cases:
– horizontal experimental tube
– vertical experimental tube, the direction of flow according to the free convection vector
– vertical experimental tube, the direction of flow not in accordance with the free convection vector
For such cases the correlation equation was defined NuT=f(Gz; y), Nu = f(Gz) and the proportion NuT/Nu was analysed.
Received on 30 March 2000 相似文献
18.
Florian J. Stadler Christian Piel Joachim Kaschta Sascha Rulhoff Walter Kaminsky Helmut Münstedt 《Rheologica Acta》2006,45(5):755-764
Linear high-density polyethylenes with molar masses M
w between 240 and 1,000,000 g/mol, obtained by metallocene catalysts, were characterized in shear using oscillatory and creep tests. The polydispersities of the molar mass distributions (MMDs) lay between 1 and 16. The resulting zero shear-rate viscosities η0 covered a range from 2.5×10−3 to around 108 Pas. Above a critical molar mass of M
c≈2,900 g/mol, the experimental results can be described by the relation η0 ∼ M
w3.6, independently of the MMD. The oscillatory data were fitted with a Carreau–Yasuda equation. The resulting parameters were correlated to molecular structure. The parameter a, being a quantity for the width of the transition between the Newtonian and the non-Newtonian regime, showed a dependence on the molar mass M
w but not on M
w/M
n. The parameter λ of the Carreau-Yasuda equation was found to be the reciprocal crossover frequency for all samples with a log-Gaussian MMD. λ depends on the molar mass M
w and also on M
w/M
n.
相似文献
Helmut MünstedtEmail: Phone: +49-9131-8527604Fax: +49-9131-8528321 |
19.
The Simha–Somcynsky (S–S) equation of state (eos) was used to compute the free volume parameter, h, from the pressure–volume–temperature (PVT) dependencies of eight molten polymers. The predicted by eos variation of h with T and P was confirmed by the positron annihilation lifetime spectroscopy; good agreement was found for h(P = constant) = h(T) as well as for h(T = constant) = h(P). Capillary shear viscosity (η) data of the same polymers (measured at three temperatures and six pressures up to 700 bars), were plotted as logη vs 1/h, the latter computed for T and P at which η was measured. In previous works, such a plot for solvents and silicone oils resulted in a “master curve” for the liquid,
in a wide range of T and P. However, for molten polymers, no superposition of data onto a “master curve” could be found. The superposition could be
obtained allowing the characteristic pressure reducing parameter, P*, to vary. The necessity for using a “rheological” characteristic pressure reducing parameter, P*R = κP*, with κ = 1 to 2.1 indicates that the free volume parameter extracted from the thermodynamic equilibrium data may not fully describe
the dynamic behavior. After eliminating possibility of other sources for the deviation, the most likely culprit seems to be
the presence of structures in polymer melts at temperatures above the glass transition, T
g. For example, it was observed that for amorphous polymers at T ≅ 1.52T
g the factor κ = 1, and the deviation vanish. 相似文献
20.
In order to evaluate characteristics of the liquid film flow and their influences on heat and mass transfer, measurements
of the instantaneous film thickness using a capacitance method and observation of film breakdown are performed. Experimental
results are reported in the paper. Experiments are carried out at Re = 250–10000, T
in = 20–50°C and three axial positions of vertically falling liquid films for film thickness measurements. Instantaneous surface
waveshapes are given by the interpretation of the test data using the cubic spline method. The correlation of the mean film
thickness versus the film Reynolds number is also given by fitting the test data. It is revealed that the surface wave has
nonlinear behavior. Observation of film breakdown is performed at Re = 1.40 × 103–1.75 × 104 and T
in = 85–95°C. From experimental results, the correlation of the film breakdown criterion can be obtained as follows: Bd = 1.567 × 10−6
Re
1.183 相似文献