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Exact Solution on Unsteady Couette Flow of Generalized Maxwell F...
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广义Maxwell流体非定常Couette流动的精确解,王少伟,徐明瑜,文章首先提出一个带分数阶导数的Maxwell模型.借助于积分变换(Laplce变换和Weber变换)和Mittag-Leffler函数,给出了模型在非定常Couette流动的精�
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Exact Solution on Unsteady Couette Flow of
Generalized Maxwell Fluid with Fractional
Derivative
1
Shaowei Wang Mingyu Xu
I
nstitute of Applied Math, School of Math. and System Science
Shandong University, Jinan, PRC 250100
wangshaowei@math.sdu.edu.cn xumingyu@163169.net
Abstract
In this paper the unsteady Couette flow of a generalized Maxwell fluid with fractional
derivative (GMF) is studied. The exact solution is obtained with the help of integral
transforms (Laplace transform and Weber transform) and generalized Mittag-Leffler
function. It was shown that the distribution and establishment of the velocity is
governed by two non-dimensional parameters
η
, b and fractional derivative
α
of
the model. The result of classical (Newtonian fluid) Couette flow can be contained as
a special case of the result given by this paper, and the decaying of unsteady part of
GMF displays power law behavior, which has scale invariance.
Keywords: unsteady Couette flow; generalized Maxwell fluid; fractional calculus;
exact solution
1 Introduction
The non-Newtonian fluids are increasing being considered more important and appropriate in
technological applications than the Newtonian fluids. Strictly speaking, the linear relation between
stress and the rate of strain does not exist for a lot of real fluids, such as blood, oils, paints and
polymeric solution. In general, the analysis of the behavior of the fluid motion of the non-Newtonian
fluids tends to be much more complicated and subtle in comparison with that of the Newtonian fluids.
There has been fairly large number of flows of Newtonian fluids for which a closed form analytical
1
This work was supported by the National Natural Science Foundation of China (Grant No. 10272067) and the
Doctoral Program Foundation of the Education Ministry of P.R. China (Grant No.20030422046).
1
http://www.paper.edu.cn
solution is possible. However, for non-Newtonian fluids such exact solutions are rare. In order to
describe the rheological properties of wide classes of materials, the rheological constitutive equations
with fractional derivatives have been introduced for a long time, which are discussed in the papers
given by Friedrich[1], Bagley[2], Glöckle and Nonnenmacher[3], Rossikhin and Shitikova[4,5],
Mainardi[6], Mainardi and Gorenflo[7], Makris and Coustantinous[8] and the references therein. And
they obtained the ideal results which are good agreement with the experimental data. The starting
point of the fractional derivative model of non-Newtonian fluid is usually a classical differential
equation which is modified by replacing the time derivative of an integer order by the so-called
Riemann-Liouville fractional differential operator.
The fluid considered in this paper is a generalized Maxwell fluid with fractional derivative (GMF).
In one dimension its constitutive equation may be expressed in terms of scalar form[1,9,10]
γκτκτ
ββαα
tt
DGD
000
=+
, (1)
where
τ
is the shear stress,
γ
is the shear strain,
0
/G
µ
κ
=
is the relaxation time and is a
shear modulus,
0
G
µ
is a viscosity constant (
0>
κ
and
0>
µ
),
α
,
β
are fractional parameters
such that
10 ≤≤≤
β
α
. And is the Riemann-Liouville (R-L) differential operator defined
as:
α
t
D
0
⎭
⎬
⎫
⎩
⎨
⎧
−
−Γ
=
∫
t
t
dz
zt
zf
dt
d
tfD
0
0
)(
)(
)1(
1
)]([
α
α
α
. (
10
<
<
α
) (2)
Furthermore, Friedrich[1] proved that this kind of rheological constitutive equation shows
fluid-like behaviors only in the case that the derivative of stress is fractional and one of strain is first
order in time. Therefore, the following constitutive equation of GMF is used in this paper:
γµτκτ
αα
&
=+
t
D
0
, (3)
where
dtd /
γ
γ
=
&
is the rate of shear strain.
The unsteady Couette flow problem has been considered in several works for a long time containing
various effects as in the book and paper given by Joseph[11], Bernardin[12] and Demirel[13]. In this
paper we use the constitutive equation (3) to study the unsteady Couette flow of GMF. By using the
Laplace transform, Weber transform and generalized Mittag-Leffler function, we get the exact solution
of the problem. It was shown that the result of classical Couette flow can be contained as a special
case of the result given by this paper and the decaying of unsteady part of GMF displays power law
behavior, which has its scale invariance.
2
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