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1.
A three-parameter model describing the shear rate-shear stress relation of viscoelastic liquids and in which each parameter has a physical significance, is applied to a tangential annular flow in order to calculate the velocity profile and the shear rate distribution. Experiments were carried out with a 5000 wppm aqueous solution of polyacrylamide and different types of rheometers. In a shear-rate range of seven decades (5 10–3 s–1 <
< 1.2 105 s–1) a good agreement is obtained between apparent viscosities calculated with our model and those measured with three different types of rheometers, i.e. Couette rheometers, a cone-and-plate rheogoniometer and a capillary tube rheometer.
a
physical quantity defined by:a = {1 – (
/
0)}/
0 (Pa–1)
-
C
constant of integration (1)
-
r
distancer from the center (m)
-
r
1,r
2
radius of the inner and outer cylinder (m)
-
v
r
local tangential velocity at a distancer from the center (v
r
=
r
r) (m s–1)
-
v
2
local tangential velocity at a distancer
2 from the center (m s–1)
-
shear rate (s–1)
-
local shear rate
(s–1)
-
1
wall shear rate at the inner cylinder (s–1)
-
dynamic viscosity (Pa s)
-
a
apparent viscosity (a = /
) (Pa s)
-
a1
apparent viscosity at the inner cylinder (Pa s)
-
0
zero-shear viscosity (Pa s)
-
infinite-shear viscosity (Pa s)
-
shear stress (Pa)
-
r
local shear stress at a distancer from the center (Pa)
-
0
yield stress (Pa)
-
1,
2
wall shear-stress at the inner and outer cylinder (Pa)
-
r
local angular velocity (s–1)
-
2
angular velocity of the outer cylinder (s–1) 相似文献
2.
Singular Solutions in an Axisymmetric Flow of a Medium Obeying the Double Shear Model 总被引:1,自引:0,他引:1
S. E. Alexandrov 《Journal of Applied Mechanics and Technical Physics》2005,46(5):766-771
An asymptotic analysis of equations of an axisymmetric flow of a rigid-plastic material obeying the double shear model in the vicinity of surfaces with the maximum friction is performed. It is shown that the solution is singular if the friction surface coincides with the envelope of the family of characteristics. A possible character of the behavior of singular solutions in the vicinity of surfaces with the maximum friction is determined. In particular, the equivalent strain rate in the vicinity of the friction surface tends to infinity in an inverse proportion to the square root from the distance to this surface. Such a behavior of the equivalent strain rate is also observed in the classical theory of plasticity of materials whose yield condition is independent of the mean stress.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 180–186, September–October, 2005. 相似文献
3.
Viscous fluid flow past an infinite periodic array of rigid spheres of the same radius is considered. A solution of the Stokes equations periodic in three variables is obtained for viscous incompressible flow with a linear velocity profile. The solution takes into account the hydrodynamic interaction of an infinite number of particles in the array. An expression for the effective viscosity of a suspension with a cubic array of particles is obtained. 相似文献
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6.
In order to expand the predictive capability of single-point turbulence closure models to account for the early-stage transition
regime, a methodology for the formulation and calibration of model equations for the ensemble-averaged disturbance kinetic
energy and energy dissipation rate is presented. The calibration is based on homogeneous shear flow where disturbances can
be described by rapid distortion theory (RDT). The relationship between RDT and linear stability theory is exploited in order
to obtain a closed set of modeled equations. The linear disturbance equations are solved directly so that the numerical simulation
yields a database from which the closure coefficients in the ensemble-averaged disturbance equations can be determined.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
本文通过数值方法求解均匀动脉中的非平稳脉动流,给出了通过测量非平稳脉动血流量确定壁面切应力的方法.作为算例,采用实测的大鼠颈总动脉流量信号,求出了均匀动脉壁面切应力波形.进一步对求得的切应力波形进行经验模态分解(EMD),得到了切应力波形的各内在模态(IMF),以及Hilbert幅值谱.从切应力波形经Hilbert-Huang变换得到的IMF和Hilbert谱图可以明显地看出切应力各频率成分的物理意义.所得结果为进一步深入研究非平稳脉动切应力与血管重建的关系提供了一种方法学基础. 相似文献
8.
刚性圆管中血液周期振荡流的切应力分布 总被引:1,自引:0,他引:1
本文通过求解圆管内血液振荡流的基本方程,求得圆管内血液流的压力梯度与切应力之间的关系式。在此基础上,详细讲座了圆管中轴向流速和切变率谐波的变化规律,指出流速谐波和切变率谐波的幅值都将随着谐波次数的增大而逐渐减小。为了使所得结果便于应用。文章通过管轴向中心线流速与压力梯度之间的关系式,进一步给出一种利用管轴向中心线流速计算管内切应力分布的简便方法。该方法用于检测活体血管内血液振荡流的切应力分布,具有操作简单,精度较高的优点。最后,以人体颈动脉为例,讨论血液周期振荡流的切应力的分布特性。发现在任意时刻,除了邻近管壁处切应力急剧增大到一定数值之外,沿管截面切应力分布相当均匀且接近于零,呈现出与定常流不同的切应力分布特征。 相似文献
9.
We investigate two different discretization approaches of a model optimal-control problem, chosen to be relevant for control
of instabilities in shear flows. In the first method, a fully discrete approach has been used, together with a finite-element
spatial discretization, to obtain the objective function gradient in terms of a discretely-derived adjoint equation. In the
second method, Chebyshev collocation is used for spatial discretization, and the gradient is approximated by discretizing
the continuously-derived adjoint equation. The discrete approach always results in a faster convergence of the conjugate-gradient
optimization algorithm. Due to the shear in the convective velocity, a low diffusivity in the problem complicates the structure
of the computed optimal control, resulting in particularly noticeable differences in convergence rate between the methods.
When the diffusivity is higher, the control becomes less complicated, and the difference in convergence rate reduces. The
use of approximate gradients results in a higher sensitivity to the degrees of freedom in time. When the system contains a
strong instability, it only takes a few iteration to obtain an effective control for both methods,even if there are differences
in the formal convergence rate. This indicates that it is possible to use the approximative gradients of the objective function
in cases where the control problem mainly consists of controlling strong instabilities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
A direct numerical simulation of turbulent channel flow with an imposed mean scalar gradient is analyzed with a focus on passive
scalar flux modelling and in particular the treatment of the passive scalar dissipation equation. The Prandtl number is 0.71
and the Reynolds number based on the wall friction velocity and the channel half width is 265. Budgets are presented for the
passive scalar variance and its dissipation rate, as well as for the individual scalar flux components. These form a basis
for a discussion of modelling issues related to explicit algebraic scalar flux modelling.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
本文建立一种分析局部缓慢狭窄血管中血液振荡流的数学模型,给出了血液的轴向流速,径向流速和切应力的包含压力梯度项的解析表达式,并讨论了血管内由局部狭窄引起的压力梯度沿轴向变化的规律。文章以局部余弦狭窄为例进行数值计算,详细讨论上游均匀管段压力梯度的定常部分和不同次谐波对狭窄管段内流速和切应力的影响。数值结果表明,与均匀管情况相比,在狭窄段内,血液振荡流轴向流速无论平均值还是脉动幅值均明显增大,且径向流速不再为零。但径向流速仍远小于轴向流速。同时,切应力也不再仅由轴向流速梯度提供,径向流速梯度也将产生切应力,但是在计算管壁切向上的切应力时,径向流速梯度的贡献仍相当大。与均匀管管壁切应力沿流运方向保持恒定不同。狭窄管管壁切应力(平均值和脉动值)将随着狭窄高度的增大而增大,在狭窄最大高度处达到最大,因而沿流动方向产生了较大的切应力梯度。 相似文献
12.
本文求解局部缓慢扩张动脉管中血液振荡流的基本方程,得到血管内血液的流速与压力梯度的关系。通过导出压力梯度沿局部扩张管轴向的变化特性。建立利用扩张段上游血管均匀段中心流速波形确定局部扩张管中血液流的速度和切应力分布的方法,文章以人体颈动脉余弦扩张为例进行分析。详细讨论了局部扩张对血管壁切应力及其梯度分布的影响。数值结果表明,在与刚性均匀管中管壁切应力沿轴向保持不变不同,在局部扩张段,管壁切应力将随着血管半径的增大而减小,因而管壁切应力梯度一般不为零,甚至在某些位置达到相当大的数值。另外,随着血管扩张程度的增加,管壁切应力还将进一步减小,而且管壁切应力梯度也将进一步增大,血管扩张导致管壁切应力的这些变化将直接影响血管壁的结构和功能,使其产生适应性的变化。 相似文献
13.
岩石分形节理粗糙性对应力场影响的光弹模拟研究 总被引:2,自引:0,他引:2
节理的粗糙性是影响岩体力学特性的重要因素。现有的众多的研究结果表明:不规则的节理面具有很好的自相似特征,可以用分形几何去描述,节理面的分形维数是表征节理面粗糙度(JRC)恰当的统计量。基于以上观点,为了能够精确地控制节理面的粗糙性,本文以Mandelbrotweierstrass函数生成不同分维的分形曲线来模拟实际的粗糙节理面,制成光弹实验试样进行多组的单压和压剪实验,通过光弹条纹和接触点的变化来研究不规则的节理对于岩体变形,应力场的影响,得出了一些有益的结论. 相似文献
14.
15.
Chanyi Song Soo Jai Shin Hyung Jin Sung Keun-Shik Chang 《Journal of Fluids and Structures》2011,27(3):438-455
The unsteady behavior of a 2-D circular elastic capsule was investigated in three viscous shear flows. An immersed boundary method (IBM) has been used to solve the dynamic fluid-structure interaction of the capsule. Computations were carried out in finite parameter ranges where the Reynolds number is Re=1-40 and the capillary number is Ca=0.0005-0.05, which is the ratio of the external viscous shear stress to the resistant elastic tensions of the membrane. For the simple shear flow, the effect of inertia on the transient behavior of the capsule was studied. For the pulsatile shear flow, two values of the peak fluid strain, Tf=1 and 5, were considered for the quasi-steady capsule mechanics. The capsule shows a cyclic structural response that includes subharmonics as the Reynolds number is elevated to 10 and 40. The capsule dynamic response includes a phase lag, which is a function of the capillary number, the Reynolds number, and the peak fluid strain. Finally, the capsule flowing in the Couette flow shows lateral migration due to the transient lift force, which is higher for lower Ca and higher Re. When capsules with diverse elasticity are dispersed along the velocity gradient, the capsule with a hard membrane experienced greater lift than the one with a soft membrane. 相似文献
16.
In the petroleum production industry wells are mostly cased and perforated in the producing formation. Perforation characteristics
such as size, length, number of perforation tunnels and their arrangements as well as fluid and rock properties determine
fluid flow behaviour in the wellbore region, hence, well productivity. Flow of gas and condensate around a perforation tunnel
(including the damaged zone) has been studied by performing steady-state core experiments and simulating the results numerically,
using a finite element modelling approach. The model allows for the changes in fluid properties and accounts for the coupling
of the two phases and the inertial effect using a fractional flow based correlation. The results indicated that different
sets of thickness-permeability (h−k) values obtained from matching single-phase flow performance could be assigned to the damaged zone around perforation to
represent the two-phase flow performance. The status of the tip of the perforation for two extreme cases of totally closed
and fully open was investigated and found to have a minimal effect on the performance of the system. 相似文献
17.
IntroductionTheflowtheoryanditsapplicationoffluidsflowinafractalreservoirhavecontinuallygonedeepintostudysinceChangandYortsos[1]builttheflowmodeloffluidthroughafractalreservoir.TONGDeng_ke[2 ]presentedtheexactsolutionanditspressurecharacteristicsfortheva… 相似文献
18.
Advanced Turbulence Modelling of Separated Flow in a Diffuser 总被引:1,自引:0,他引:1
The paper describes an investigation into the predictive performance of linear and non-linear eddy-viscosity models and differential
stress-transport closures for separated flow in a nominally two-dimensional, asymmetric diffuser. The test case forms part
of a broader collaborative exercise between academic and industrial partners. It is demonstrated that advanced turbulence
models using strain-dependent coefficients and anisotropy-resolving closure offer tangible advantages in predictive capability,
although the quality of their performance can vary significantly, depending on the details of closure approximations adopted.
Certain features of the flow defy resolution by any of the closures investigated. In particular, no model resolves correctly
the flow near the diffuser's inclined wall immediately downstream of the inlet corner, which may reflect the presence of a
“flapping” motion associated with a highly-localised process of unsteady separation and reattachment.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
A time-dependent three-dimensionally skewed flow is investigated using direct numerical simulations of the incompressible
Navier-Stokes equations. The effect on the instantaneous and mean turbulent field is investigated. Instantaneous flowfields
reveal that the skewing has the effect of initially reducing the strength and height of quasi-streamwise vortices of both
signs of rotation with respect to the skewing. A mechanism for this process is put forward. The mean flowfields show drops
in turbulence quantities such as turbulence kinetic energy. In addition to this, two-equation turbulence modelling of the
flow is carried out. This highlights a deficiency, in that the standard turbulence models are unable to capture the drop in
turbulence intensity due to the skewing. A modification based on the exact dissipation equation is found to significantly
improve the model behaviour for this flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
搅拌槽流场的实验研究 总被引:4,自引:0,他引:4
利用二维激光多普勒测速仪在内径为250mm的搅拌槽内对DT叶轮和PT叶轮进行了流场测试,获得了不同几何参数的叶轮在不同工况下的二维时均速度场和湍流强度、雷诺应力、剪切速率分布。为进一步研究搅拌器的流动特性,开发新型搅拌叶轮提供了可靠的实验依据。 相似文献