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1.
Characteristics of the fields of mean density and density fluctuations measured with introduction of periodic disturbances
into a hypersonic viscous boundary layer on a flat plate are presented. The experiments are performed for a flow Mach number
M∞ = 21, Reynolds number per meter Re1∞ = 6·105 m−1, and temperature factor of the surface T
w
/T
0 = 0.26. The disturbances are introduced into the shock layer by an oblique gasdynamic whistle.
The work was financially supported by the Russian Foundation for Basic Research (Grants Nos. 04-01-00474 and 05-08-33436). 相似文献
2.
3.
The results are presented for numerical modelling of two-dimensional flows with large pressure gradients in a wide range of
freestream parameters (M = 2−4, Re
1
= 5−30·106 1/m) and the intensities of perturbing factors. Computations were performed with the use of averaged unsteady Navier — Stokes
equations of a viscous heat-conducting gas. The structure of a turbulent boundary layer at its passage through a single shock
and a system of shocks of different strengths, which lie at a fixed distance from one another, was investigated numerically.
In the case of the boundary layer passage through a system of shocks, the influence of the first interaction on the structure
and separation properties of the boundary layer behind the second shock was investigated. The presence of a preliminary shock
was shown to improve the boundary layer capability to withstand separation ahead of the secondary interaction region. 相似文献
4.
Development of three-dimensional turbulent separation in the neighborhood of incident crossing shock waves 总被引:1,自引:1,他引:0
The results are presented for experimental investigation of the peculiarities of the development of three-dimensional turbulent
separated flows on a flat surface for the Mach number M∞ = 4 and the Reynolds number Re1 ∼ 55·106 m−1 under the conditions of the flow around two identical cylindrical bodies of revolution of diameter D = 50 mm and the body aspect ratio L
b/D = 5 with conical forebodies with semi-apex angles βc = 30, 20, 15, and 10° located above plate in parallel to one another and to the flow. The typical stages of the three-dimensional
separation development are considered under the reducing distance between the axes of the bodies within the range of Z = Δz/D = 1.06–3.0 at their fixed distance from the surface (Y = Δy/D = 0.96). The topology of limiting streamlines and the peculiarities of pressure fields on the surface as well as the gasdynamic
structure of separated flows arising at the interaction of crossing bow shocks propagating from the bodies and at the interaction
of secondary disturbances with the boundary layer are analysed. 相似文献
5.
V. I. Kornilov 《Thermophysics and Aeromechanics》2009,16(3):347-354
The transition of the boundary layer from the laminar to the turbulent state on a smooth flat plate at a zero angle of attack
is studied in the range of Mach numbers M∞ = 2–6. It is demonstrated that the results measured at the end of the transition region can be approximated by a simple dependence
suitable for applications, which does not require additional measurements, is valid in the range of Mach numbers M∞ = 2–10, and, with an error lower than 20 %, can be used to estimate the location of the transition region on a flat plate
in geometrically similar wind tunnels. 相似文献
6.
V. I. Kornilov 《Thermophysics and Aeromechanics》2010,17(2):249-258
Experiments are performed to study the possibility of decreasing the net drag of a flat plate with the use of streamwise-oriented
vertical elements mounted normal to the surface in an incompressible equilibrium turbulent boundary layer. The Reynolds number
based on the boundary-layer momentum thickness in the section where the vertical elements are placed is 820. It is demonstrated
that vertical large eddy breakup elements with the geometry used do not reduce the drag of a flat plate in the major part
of the range of Reynolds numbers Re
x
examined. It is only at extremely low values of Re
x
that a certain gain in the net drag is reached, as compared with the value for a non-modified flow. 相似文献
7.
HUANG ZhangFeng ZHOU Heng & LUO JiSheng Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University Tianjin University Tianjin China 《中国科学G辑(英文版)》2007,50(3):348-356
Through temporal mode direct numerical simulation, flow field database of a fully developed turbulent boundary layer on a flat plate with Mach number 4.5 and Reynolds number Reθ =1094 has been obtained. Commonly used detection meth- ods in experiments are applied to detecting coherent structures in the flow field, and it is found that coherent structures do exist in the wall region of a supersonic turbulent boundary layer. The detected results show that a low-speed streak is de- tected by using the Mu-level method, the rising parts of this streak are detected by using the second quadrant method, and the crossing regions from a low-speed streak to the high-speed one are detected by using the VITA method respectively. Notwithstanding that different regions are detected by different methods, they are all accompanied by quasi-stream-wise vortex structures. 相似文献
8.
《Combustion Theory and Modelling》2013,17(2):173-187
The catalytic ignition of dry carbon monoxide and air in a boundary layer flow over a palladium plate is studied in this paper. The heterogeneous reaction mechanism is modelled with the dissociative adsorption of the molecular oxygen and the non-dissociative adsorption of CO, together with a surface reaction of the Langmuir-Hinshelwood type and the desorption reaction of the adsorbed product, CO2(s). The critical condition for catalytic ignition, represented by the ignition Damköhler number, has been deduced using high activation energy asymptotics of the desorption kinetics of the most efficiently adsorbed reactant, CO(s). Longitudinal heat conduction along the plate has been considered and its influence on the ignition temperature has been evaluated. This influence is rather weak, indicating that the flat plate boundary layer flow configuration is a robust device to determine the critical conditions for catalytic ignition. 相似文献
9.
The effect of high pressure on the crystal structure of the intermetallic compounds R2Fe17 − x
Six (R = Lu or Y; x = 0 or 1.7) was studied using neutron diffraction. A correlation between changes in structural parameters and magnetic properties
under the action of high pressure, as well as under chemical substitution of Si for Fe atoms, was analyzed in terms of localized
moment and spin fluctuation models. The spin fluctuation model was found to describe more adequately the experimentally observed
increase in the Curie temperature upon chemical substitution and the decrease in this temperature under the action of high
pressure. Possible reasons for the suppression of a collinear ferromagnetic state and the occurrence of a noncollinear antiferromagnetic
state in R2Fe17−x
Six under pressure are discussed based on estimated differences between the total energy minima of these states.
Original Russian Text ? D.P. Kozlenko, V.I. Voronin, V.P. Glazkov, B.N. Savenko, 2007, published in Pis’ma v Zhurnal éksperimental’noĭ
i Teoreticheskoĭ Fiziki, 2007, Vol. 86, No. 9, pp. 675–680. 相似文献
10.
11.
Abstract
Evolution of the Λ-vortex and its transformation into the turbulent spot in a flat plate boundary layer are investigated experimentally. Extensive measurements visualizing the Λ-structure transformation into the turbulent spot on the smooth and ribbed surfaces of the flat plate are presented. The flow behavior in the course of spatial evolution of the Λ-structure and turbulent spot is discussed. Specific features of the downstream evolution of Λ-structure and turbulent spot on the smooth and ribbed surfaces are demonstrated, such as suppression by riblets of the Λ-vortex transformation into the turbulent spot, appearance of the coherent structures of Λ-vortex within ensemble-averaged turbulent spot, and oblique waves generation both by the Λ-vortex and turbulent spot. 相似文献12.
In this paper, hot-wire anemometry (HWA) is used to experimentally investigate interactions between a fully developed turbulent boundary layer and wake of an elliptic cylinder where axis ratio (AR) of the cylinder is 2. The elliptic cylinder was located inside and outside a turbulent boundary layer with a thickness (δ) of 0.38B. Furthermore, experiments were conducted at different Reynolds numbers (13,250 and 26,500) based upon the smallest cylinder diameter (B). Mean velocity, turbulence intensity and higher-order central moments of velocity signals (i.e. skewness and flatness) measurements were performed using HWA upon wake-boundary layer interactions on a flat plate. Results showed that profiles of stream-wise mean velocity and turbulence intensity were greatly dependent on gap ratio (G/B) and Reynolds number (Re) in near-wake region. It was also observed that, except for G/B = 0.1, the wake-boundary layer interactions were faster at Reynolds number of 26,500 rather than 13,250. The interactions occurred earlier upon fluctuating the velocity rather than the case where a fixed mean velocity was considered. The results further show that an increase in the gap ratio increases Strouhal number almost independent of δ/B. Behind the cylinder, relatively smaller wake region was obtained at Re = 26,500 rather than Re = 13,250, where the velocity profiles quickly converged to the flat plate boundary layer velocity profiles. 相似文献
13.
A. Di Giacomo E. Meggiolaro Yu. A. Simonov A. I. Veselov 《Physics of Atomic Nuclei》2007,70(5):908-924
It is argued that strong dynamics in the quark-gluon plasma and bound states of quarks and gluons is mostly due to nonperturbative
effects described by field correlators. The emphasis in the paper is made on two explicit calculations of these effects from
first principles—one analytic using gluelump Green’s functions and another using independent lattice data on correlators.
The resulting hadron spectra are investigated in the range T
c
≤ T < 2T
c
. The spectra of charmonia, bottomonia, light s
mesons, glueballs, and quark-gluon states calculated numerically are in general agreement with lattice MEM data. The possible
role of these bound states in the thermodynamics of quark—gluon plasma is discussed.
The text was submitted by the authors in English. 相似文献
14.
On an ESFADOF edge-filter for a range resolved Brillouin-lidar: The high vapor density and high pump intensity regime 总被引:1,自引:0,他引:1
The temperature profile in the upper ocean mixed layer is of great interest for oceanography, weather forecast and climate
studies—especially regarding the strong coupling between the atmosphere and the ocean. A lidar system based on Brillouin-scattering
can provide such data over an extended region of the ocean. In this paper we report on studies of an excited-state Faraday
anomalous dispersion optical (ESFADOF) edge-filter that, when employed as a receiver in a Brillouin-lidar, will enable range-resolved
remote measurements from mobile platforms. We focus on the transmission of such a filter operating on the 5P
3/2→8D
5/2 Rb transition (543.30 nm), and its dependence on the vapor density in the high pump intensity regime. Due to quenching processes
such as energy-pooling enhanced by nonlinear radiation trapping, as well as plasma formation, a limit on the lower ESFADOF
level number density exists. Beyond this threshold the achievable ESFADOF transmission is limited to a few percent. However,
our studies show for the first time measured ESFADOF spectra with steep transmission edges with a transmission change of 15%
within a few gigahertz. 相似文献
15.
L. P. Ol’khovik Z. I. Sizova E. V. Shurinova A. S. Kamzin 《Physics of the Solid State》2010,52(2):311-316
This paper reports on a study of the field and temperature dependences of the parameters of the particle magnetic interaction
in a densely packed system of nanocrystals of the highly anisotropic hexagonal ferrite BaFe12O19 with the particles distributed in diameter within the range 10—100 nm and having volumes satisfying the criterion of “small
Stoner—Wohlfarth particles.” It is shown that the resultant particle interaction in the temperature range 300 K≤T≤640 K has a negative sign, whereas for T>640 K, it is positive. The maximum values of the parameter Δm allow classification of the interaction as moderate in strength. The temperature dependences of the interaction parameters
are found to correlate with manifestation of the size and surface effects in the system, which are characteristic of small
particles (transition to the superparamagnetic state, “surface” anisotropy, and reduced exchange interaction in a structurally
defective near-surface layer of particles). 相似文献
16.
F. N. Ibrahim 《Il Nuovo Cimento D》1995,17(10):1089-1101
Summary Analytical and numerical solutions for the momentum and thermal boundary layer equations of a non-Newtonian power law fluid
are presented. The flow is assumed to be under the influence of an external magnetic fieldB (x) applied perpendicular to the surface and an electric fieldE(x) perpendicular toB(x) and the direction of the longitudinal velocity in the boundary layer. For the power law fluid it is assumed that the shear
stress is proportional to then-th power of the velocity gradient andn is called the flow index. The variations of the velocity fieldf′, the temperature field θ, the shear stress on the surfaceτ
W
, the displacement thicknessδ
1 and the momentum thicknessδ
2 with the magnetic-field parameter γ, the flow indexn, the heat transfer indexS and the Prandtl number Pr are studied. It is found that, if the outer flow velocityU(x) (potential flow) is proportional to the arc lengthx raised to a powerm, then the similarity solution for the thermal boundary layer equation is possible only whenm=1/3, which represents flow past a wedge of included angle π/2. It is established that the temperature of the wedge increases
with the increase of γ, Pr,S and the decrease ofn. In general the magnetic field can be used as a heater for the surface of the wedge. 相似文献
17.
AC impedance spectroscopy technique has been used to study electrical properties of Bi3.25La0.75Ti3O12 (BLT) ceramic. Complex impedance plots were fitted with three depressed semicircles, which are attributed to crystalline
layer, plate boundary and grain boundary and all three were found to comprise of universal capacitance nature [C = C0w
n−1]. Grain boundary resistance and capacitance evaluated from complex impedance plots have larger values than that of plate
boundary and crystalline layer. The activation energies (E
a) for DC-conductance in grain boundary, plate boundary and crystalline layer are 0.68 eV, 0.89 eV and 0.89 eV, respectively.
Relaxation activation energies calculated from impedance plots showed similar values, 0.81 eV and 0.80 eV for crystalline
layer and plate boundary, respectively. These activation energy values are found to be consistent with the E
a value of oxygen vacancies in perovskite materials. A mechanism is offered to explain the generation of oxygen vacancies in
BLT ceramic and its role in temperature dependence of DC-conductance study.
相似文献
18.
In this work the problem of diffusion in the definite diffusion field whose one boundary is fixed and the other — interphase
boundary — moves in time according to the parabolic law. The mathematical problem is solved exactly by means of thermal potentials
of a double layer. The solution of the diffusion equation in the proximity to the boundary was derived and the concentration
gradients on these boundaries were calculated. The numerical procedure of determining the diffusion characteristics from experimental
concentration gradients on the phase boundaries was presented. As the zero approximation the result of calculations according
to Wagner’s solution was used.
Theory.
Numerical calculations. 相似文献
19.
A study has been carried out of the temperature dependences of luminescence spectra on a large number of CdTe/ZnTe structures
differing in average thickness, 〈L
z〉=0.25–4 monolayers (ML), and CdTe layer geometry (continuous, island type). The influence of geometric features in the structure
of ultrathin layers on linewidth, the extent of lateral localization of excitons, their binding energy, and exciton-phonon
coupling is discussed. It is shown that in island structures there is practically no lateral exciton migration. The exciton-phonon
coupling constant in a submonolayer structure has been determined, Γph=53 meV, and it is shown that in structures with larger average thicknesses Γph is considerably smaller. Substantial lateral exciton migration was observed to occur in a quantum well with 〈L
z〉=4 ML, and interaction with acoustic phonons was found to play a noticeable part in transport processes. It has been established
that the depth of the exciton level in a quantum well and structural features of an ultrathin layer significantly affect the
temperature dependences of integrated photoluminescence intensity.
Fiz. Tverd. Tela (St. Petersburg) 41, 717–724 (April 1999) 相似文献
20.
The optical characteristics of a UV broadband lamp that was excited by a longitudinal glow discharge and operated on Kr—Br2—I2, Xe—Br2—I2, and Kr—Xe—Br2—I2 mixtures are investigated. The interelectrode spacing in the lamp is 10 cm, the inner diameter of a discharge tube being
14 mm. The current-voltage characteristics, the emission spectra of the plasma, and the dependence of the intensity of spectral
lines (the amplitude of radiation bands) on the power that was pumped into the plasma based on mixtures of various compositions
and pressures, as well as the radiation power in the spectral range from 200 to 390 nm, are studied.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 6, pp. 840–842, November–December, 2005. 相似文献