共查询到20条相似文献,搜索用时 26 毫秒
1.
黄景泉 《应用数学和力学(英文版)》1990,11(8):773-778
The paper analyzes the noise at inception and collapse of an isolated bubble cavity filled with gas and vapour. The expressions and their numerical solutions of the sound pressure and the vibration velocity are presented.
The results indicate that the noise occurs at every stage of a cavity. The noise has comparatively big value only at the late period of collapse. The sound pressure is of magnitude 100db. 相似文献
2.
High-speed tomographic PIV was used to investigate the coalescence of drops placed on a liquid/liquid interface; the coalescence
of a single drop and of a drop in the presence of an adjacent drop (side-by-side drops) was investigated. The viscosity ratio
between the drop and surrounding fluids was 0.14, the Ohnesorge number (Oh = μd/(ρdσD)1/2) was 0.011, and Bond numbers (Bo = (ρ
d
− ρ
s
)gD
2/σ) were 3.1–7.5. Evolving volumetric velocity fields of the full coalescence process allowed for quantification of the velocity
scales occurring over different time scales. For both single and side-by-side drops, the coalescence initiates with an off-axis
film rupture and film retraction speeds an order of magnitude larger than the collapse speed of the drop fluid. This is followed
by the formation and propagation of an outward surface wave along the coalescing interface with wavelength of approximately
2D. For side-by-side drops, the collapse of the first drop is asymmetric due to the presence of the second drop and associated
interface deformation. Overall, tomographic PIV provides insight into the flow physics and inherent three-dimensionalities
in the coalescence process that would not be achievable with flow visualization or planar PIV only. 相似文献
3.
Results of one-dimensional calculations for unsteady state diffusion of a vapour in a closed tube are compared to calculations (a) for unsteady state diffusion of a vapour in an open tube, and (b) for heat conduction in a finite slab and an infinite slab. In the cases of (b) the effect of the convective term in the transport equation is absent.The total pressure is calculated and differences in the two cases are explained.An experiment is described in which the pressure increase in a closed tube due to the diffusion of water vapour in dry air is measured as a function of time. The experimental results agree quite well with the theoretical predictions. The results of this investigation may be used for the experimental determination of the diffusion coefficient of a vapour in a gas and in pressure measurements in systems with an evaporating liquid.Nomenclature
a
thermal diffusivity
-
D
diffusion coefficient
-
w
mean particle velocity
-
g
particle flux in the laboratory system
-
g*
particle flux in a system moving with the mean particle velocity w
-
L
length of the tube
-
n
number density of molecules
-
n
vs
saturation number density of vapour molecules
-
p
pressure
-
p
vs
saturation pressure of the vapour
-
t
time
-
z
distance from the liquid surface
-
N
total quantity of evaporated liquid 相似文献
4.
The influence of the type of gas on the performance of microbubble skin friction reduction was investigated on an axisymmetric
body. Gases were selected which covered a wide range of densities and solubilities. Integrated skin friction measurements,
which span a range of velocities (U
∞) from roughly 10 to 20 m/s and tunnel pressures from 1 to 2.6 atm, are presented as a function of gas flow rate. All gases
show qualitatively similar behavior. The gas volume flowrate, referenced to injector ambient conditions (tunnel temperature
and pressure), is shown to correlate the drag reducing behavior of all the gases at one velocity, independent of pressure.
A normalization based on the volume flowrate through the turbulent boundary layer is shown to nearly collapse all the results
independent of velocity or pressure. The results indicate that high ambient pressures may degrade the drag reducing capabilities
of highly soluble gases. 相似文献
5.
Rong Sheng 《Acta Mechanica Sinica》1990,6(2):128-132
In this paper, the basic equations of two-phase liquid metal flow in a magnetic field are derived, and specifically, two-phase
liquid metal MHD flow in a rectangular channel is studied, and the expressions of velocity distribution of liquid and gas
phases and the ratioK
0 of the pressure drop in two-phase MHD flow to that in single-phase are derived. Results of calculation show that the ratioK
0 is smaller than unity and decreases with increasing void fraction and Hartmann number because the effective electrical conductivity
in the two-phase case decreases.
The Project is supported by the National Natural Science Foundation of China. 相似文献
6.
Single cavitation bubbles exhibit severe modeling and simulation difficulties. This is due to the small scales of time and space as well as due to the involvement of different phenomena in the dynamics of the bubble. For example, the compressibility, phase transition, and the existence of a noncondensable gas inside the bubble have strong effects on the dynamics of the bubble. Moreover, the collapse of the bubble involves the occurrence of critical conditions for the pressure and temperature. This adds extra difficulties to the choice of equations of state. Even though several models and simulations have been used to study the dynamics of the cavitation bubbles, many details are still not clearly accounted for. Here, we present a numerical investigation for the collapse and rebound of a laser‐induced cavitation bubble in liquid water. The compressibility of the liquid and vapor are involved. In addition, great focus is devoted to study the effects of phase transition and the existence of a noncondensable gas on the dynamics of the collapsing bubble. If the bubble contains vapor only, we use the six‐equation model for two‐phase flows that was modified in our previous work [A. Zein, M. Hantke, and G. Warnecke, J. Comput. Phys., 229(8):2964‐2998, 2010]. This model is an extension to the six‐equation model with a single velocity of Kapila et al. (Phys. Fluid, 13:3002‐3024, 2001) taking into account the heat and mass transfer. To study the effect of a noncondensable gas inside the bubble, we add a third phase to the original model. In this case, the phase transition is considered only at interfaces that separate the liquid and its vapor. The stiffened gas equations of state are used as closure relations. We use our own method to determine the parameters to obtain reasonable equations of state for a wide range of temperatures and make them suitable for the phase transition effects. We compare our results with experimental ones. Also our results confirm some expected physical phenomena. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
Q. X. Wang K. S. Yeo B. C. Khoo K. Y. Lam 《Theoretical and Computational Fluid Dynamics》2005,19(5):303-317
During the collapse of a bubble near a surface, a high-speed liquid jet often forms and subsequently impacts upon the opposite
bubble surface. The jet impact transforms the originally singly-connected bubble to a toroidal bubble, and generates circulation
in the flow around it. A toroidal bubble simulation is presented by introducing a vortex ring seeded inside the bubble torus
to account for the circulation. The velocity potential is then decomposed into the potential of the vortex ring and a remnant
potential. Because the remnant potential is continuous and satisfies the Laplace equation, it can be modelled by the boundary-integral
method, and this circumvents an explicit domain cut and associated numerical treatment. The method is applied to study the
collapse of gas bubbles in the vicinity of a rigid wall. Good agreement is found with the results of Best (J. Fluid Mech.
251 79–107, 1993), obtained by a domain cut method. Examination of the pressure impulse on the wall during jet impact indicates
that the high-speed liquid jet has a significant potential for causing damage to a surface. There appears to be an optimal
initial distance where the liquid jet is most damaging. 相似文献
8.
Edmund Christiansen 《Archive for Rational Mechanics and Analysis》1986,91(2):119-135
The existence and regularity of collapse solutions in limit analysis of a plastic continuum is examined. Collapse fields for stresses and velocity exist as a saddle point for the duality between the static and kinematic formulations. The velocity field is defined as a pair u = (u
, u
T), where u
is of bounded deformation in , while uT is the velocity of the surface. A generalized Green's formula for the collapse fields is proved under certain regularity conditions. 相似文献
9.
Under certain conditions of liquid flow through rotating channels, the Coriolis force can induce a free surface to be formed. This problem is of practical importance in a Coriolis wear tester, which is used for determining the sliding wear coefficient of wear materials in slurry handling equipment. A deforming Galerkin finite element method is presented for predicting two‐dimensional turbulent free surface mean flow in rotating channels. Reynolds‐averaged Navier–Stokes (RANS) equations are cast into weak(algebraic) form using primitive variables (velocity and pressure). Eddy viscosity is determined via a mixing length model. Velocity is interpolated biquadratically, while pressure is interpolated bilinearly. The kinematic condition is used to form the Galerkin residual for the free surface. The free surface is represented by Hermite polynomials of zeroeth order for continuity of position and slope. Combined Newton's iteration is used to simultaneously solve for the free surface and the field variables. Results of velocity and pressure fields, as well as the free surface are shown to converge with mesh‐size refinement. There is excellent respect for mass conservation. Results are presented for various values of Rossby number (Ro) and height‐based Reynolds number (ReH). Parameter continuation in Ro and ReH space is used to compute solutions at higher values of flow rate and angular velocity. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
10.
The pressure melting processes of a block of ice around a moving, horizontal, elliptical cylinder are investigated. The film thickness of liquid and the relation between the force exerted on the elliptical cylinder and the melting velocity are obtained analytically. The results include those of pressure melting around a horizontal cylinder, and are discussed and compared with that of ΔT-driven melting around an elliptical cylinder. The basic differences between Δp-driven and ΔT-driven melting are obtained. Some important conclusions are drawn. 相似文献
11.
Atomization characteristics on the surface of a round liquid jet 总被引:3,自引:0,他引:3
12.
Temperature and velocity measurements are performed to clarify the effects of sub-millimeter-bubble injection on the transition
to turbulence in the natural convection boundary layer along a vertical plate in water. In particular, we focus on the relationship
between the bubble injection position L and the transition to turbulence in the natural convection boundary layer. The bubble injection positions used in our experiments
are L = 1.6 and 3.6 mm. Bubble injection at L = 1.6 mm delays the transition to turbulence in the natural convection boundary layer, while that at L = 3.6 mm accelerates the transition to turbulence in the boundary layer. In the case of L = 1.6 mm, the appearance region of the liquid velocity fluctuation in the bubble-induced upward flow in the upstream unheated
section is restricted to near the wall, although the peak of the liquid velocity fluctuation is high. In contrast, in the
case of L = 3.6 mm, the relatively large liquid velocity fluctuation is distributed widely over the laminar boundary layer width. These
results suggest that the effect of the liquid velocity fluctuation on the laminar boundary layer is quite different between
L = 1.6 and 3.6 mm. It is therefore expected that the transition to turbulence in the natural convection boundary layer for
the case with bubble injection is dependent on the magnitude and appearance region of the liquid velocity fluctuation in the
bubble-induced upward flow in the upstream unheated section. 相似文献
13.
V. G. Sokolov 《Fluid Dynamics》1970,5(4):651-655
The article describes a method for calculating the flow of heat through a wavy boundary separating a layer of liquid from a layer of gas, under the assumption that the viscosity and heat-transfer coefficients are constant, and that a constant temperature of the fixed wall and a constant temperature of the gas flow are given. A study is made of the equations of motion and thermal conductivity (without taking the dissipation energy into account) in the approximations of the theory of the boundary layer; the left-hand sides of these equations are replaced by their averaged values over the layer. These equations, after linearization, are used to determine the velocity and temperature distributions. The qualitative aspect of heat transfer in a thin layer of viscous liquid, under regular-wavy flow conditions, is examined. Particular attention is paid to the effect of the surface tension coefficient on the flow of heat through the interface.Notation x, y
coordinates of a liquid particle
- t
time
- v and u
coordinates of the velocity vector of the liquid
- p
pressure in the liquid
- cv, , T,, andv
heat capacity, thermal conductivity coefficient, temperature, density, and viscosity of the liquid, respectively
- g
acceleration due to gravity
-
surface-tension coefficient
- c
phase velocity of the waves at the interface
- Tw
wall temperature
- h0
thickness of the liquid layer
- u0
velocity of the liquid over the layer
Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 147–151, July–August, 1970. 相似文献
14.
Effect of initial conditions on a circular jet 总被引:2,自引:0,他引:2
Two circular jets are considered. One issues from a contraction with a laminar top-hat velocity profile. The other exits
from a pipe with a fully developed turbulent mean velocity profile. In spite of the significantly different initial conditions,
spectra of axial and radial velocity fluctuations in the far field (x≳30d, where d is the jet diameter) collapse over scales ranging from the Kolmogorov length scale to a length scale characterizing the organized
motion. This agreement is consistent with the observation that, at the measurement station, the large-scale anisotropy is
unchanged between the two flows.
Received: 21 September 2000/Accepted: 5 March 2001 相似文献
15.
I. G. Malenkov 《Journal of Applied Mechanics and Technical Physics》1968,9(6):750-754
An equation is derived for the ascent velocity of large gas bubbles in a liquid. This velocity is assumed to be governed by the propagation of a wavelike perturbation caused by the bubble in the liquid.Notation w
bubble (or drop) velocity
-
specific gravity
-
dynamic viscosity
-
kinematic viscosity
- r
bubble (or drop) radius
-
surface tension
-
coefficient of friction
- g
gravitational acceleration
- D
bubble (or drop) diameter
- p
pressure
- c
propagation velocity of the wavelike perturbation
-
wavelength 相似文献
16.
This study centres round the problem of flow of a liquid past a vertical porous flat plate. Considering two cases, when the plate is stationary and when it is in motion, the effect of porosity on the flow has been determined. It is found that, when the plate is stationary, the velocity of the liquid increases with increase in the suction velocity and decreases with increase in the injection velocity, and for a given suction or injection velocity, the velocity of the liquid increases with increase in time and approaches to the steady state case. But, when the plate is in motion, the velocity of the liquid decreases with increase in the suction velocity and increases with increase in the injection velocity in the constant film thickness region and also in the dynamic meniscus region provided that the gravitational force is greater than the surface tension force. In this case, the stagnation point and the minimum pressure point on the free surface have also been determined. In the case of injection there always exists a unique stagnation point and also a minimum pressure point. But in the case of suction the stagnation point does not always exist and there is no minimum pressure point.Nomenclature
A
n
roots of equation (3.18)
-
C
function defined by equation (4.20)
-
C
n
coefficients defined by equation (4.15)
-
F
function of R
0 and T
0 defined by equation (4.23)
-
g
acceleration of gravity
-
h
film thickness at any point
-
h
0
film thickness in the constant thickness region
-
h
m
film thickness at the minimum pressure point
-
h
st
film thickness at the stagnation point
-
L
m
location of the minimum pressure point=h
m
/h
0
-
L
st
location of the stagnation point=h
st/h
0
-
n
summation index
-
N
function defined by equation (4.11)
-
p
pressure
-
q
flow rate
-
q
0
flow rate in the constant thickness region
-
Q
non-dimensional flow rate
-
R
suction or injection Reynolds number=v
0
h
0/v
-
R
0
suction or injection Reynolds number corresponding to the constant thickness region=v
0
h/
-
t
time
-
T
non-dimensional time=t/h
2
-
T
0
non-dimensional parallel flow film thickness=h
0(g/u
w
)1/2
-
u
vertical velocity
-
u
perturbation velocity for u
-
u
s
surface velocity
-
u
W
withdrawal velocity of the plate
-
U
steady part of the velocity u for the stationary plate
-
non-dimensional velocity=u/gh
2
-
U*
non-dimensional velocity=U/gh
2
-
v
horizontal velocity
- v
perturbation velocity for V
-
v
0
velocity of suction or injection
-
V
transient part of the velocity u for stationary plate
-
x, y
coordinates
-
X
non-dimensional x-coordinate=x
2/gh
4
-
Y
non-dimensional y-coordinate=y/h
Greek Symbols
n
roots of equation (3.14)
-
n
eigenvalues defined by equation (4.13)
-
n
functions defined by equation (4.14)
-
n
eigenvalues defined by equation (3.15)
-
n
non-dimensional eigenvalues=
n
h/
-
kinematic viscosity
-
liquid density
-
surface tension of the liquid air interface
-
stream function
-
non-dimensional stream function=/gh
3 相似文献
17.
Employing saturated water and R-113 at atmospheric pressure, experiments are made for critical heat flux (CHF) on a uniformly heated plate of 10, 15 and 20 mm in length submerged parallel to a uniform liquid flow with velocity of 1.5–10 m/s and the data of CHF obtained are successfully correlated by a generalized equation. In addition, it is shown that existing data of CHF for acetone, toluene, monoisopropylbiphenyl and water flowing through internally heated annular channels of very small I/dhe, where I is the axial length and dhe the heated equivalent diameter, agree well with the above-mentioned correlation. 相似文献
18.
An experimental study on the interaction between Taylor bubbles rising through a co-current flowing liquid in a vertical
tube with 32 mm of internal diameter is reported. The flow pattern in the bubble's wake was turbulent and the flow regime
in the liquid slug was either turbulent or laminar. When the flow regime in the liquid slug is turbulent (i) the minimum distance between bubbles above which there is no interaction is 5D-6D; (ii) the bubble's rising velocity is in excellent agreement with the Nicklin relation; (iii) the experimental values of the bubble length compare well with theoretical predictions (Barnea 1990); (iv) the distance between consecutive bubbles varied from 13D to 16D and is insensitive to the liquid Reynolds number. When the flow regime in the liquid slug is laminar (i) the wake length is about 5D-6D; (ii) the minimum distance between bubbles above which there is no interaction is higher than 25D; (iii) the bubble's rising velocity is significantly smaller than theoretical predictions. These results were explained in the
light of the findings of Pinto et al. (1998) on coalescence of two Taylor bubbles rising through a co-current liquid.
Received: 2 February 2000 / Accepted: 15 March 2001 相似文献
19.
This work continues the studies of Khoo et al. (Exp. Fluids 29: 448–460, 2001), where experiments were performed in turbulent-channel
and flat-plate boundary-layer flows using near-wall hot-wire probes. The probability density function (pdf) of the wall-shear
stress and streamwise velocity fluctuations in the viscous sublayer, buffer region and beyond were compared and analyzed.
The convective velocity U
c of the streamwise velocity fluctuations in the very near-wall region was obtained using a two-point correlation technique.
It was found that in the viscous sublayer, U
c is approximately constant at 13u
τ
and 15u
τ
, respectively, for the channel and boundary-layer flows. Spectra data for the viscous sublayer are presented for the first
time, and the normalized spectral plots for different flow conditions collapse at high frequencies or wavenumbers, thus indicating
the possible presence of small-scale universality at different Reynolds numbers. The integral time scale corresponding to
the streamwise velocity fluctuations in the viscous sublayer is also presented.
Received: 18 October 2000/Accepted: 2 April 2001 相似文献
20.
《力学学报》2009,41(1):8
根据考虑了液体可压缩性的改进的微气泡动力学方程,采用改进的初始半径对单泡超声空化现象进行了数值计算研究. 结果表明,微气泡振动对一些参量很敏感:微气泡振动半径与初始半径的比值随振动频率的增大而减小;提高声场声压会加剧气泡崩塌程度,但过高的声压又不能使微气泡崩塌;微气泡崩塌速率随气泡初始半径的增加而增大,在一定范围内能保证空化泡稳定振动,在初始半径为1.6\,$\mu$m 处空化程度最强,如果继续增大初始半径则空化程度减弱、甚至消失;微气泡崩塌程度随黏滞系数和表面张力的增大而减弱,过大的黏滞系数和表面张力会使微气泡崩塌难以发生. 计算结果与他人的实验数据相比,发现液体的可压缩性使单泡空化强度增强, 对最佳空化区域范围的确定有较大的影响. 相似文献