Abstract
In this paper, the problem of magnetohydrodynamic (MHD) flow of a viscous fluid on a nonlinear porous shrinking sheet is studied. The boundary layer partial differential equations are first transformed into an ordinary differential equation, which is then solved numerically by the shooting method. The features of the flow for various governing parameters are presented and discussed in detail. It is found that dual solutions only exist for positive values of the controlling parameter.
MSC: 34B15, 76D10.
Keywords:
boundary layer; dual solutions; magnetohydrodynamic; shrinking sheet; numerical solution1 Introduction
Boundary layer flow over a stretching sheet has been studied in various aspects since the pioneering work done by Sakiadis [1]. Lately, many researchers have studied the shrinking sheet boundary layer flow problem due to its important applications in industries which involve packaging process, for example, shrink wrapping. The study on shrinking sheet was first initiated by Wang [2] by considering the stretching deceleration surface. Miklavcic and Wang [3] proved the existence and uniqueness for viscous flow due to a shrinking sheet, and dual solutions were reported for certain range of the suction parameter. Later, Wang [4] also studied the stagnation flow towards a shrinking sheet by considering the twodimensional and axisymmetric stagnation flows, and dual solutions were also reported only for the twodimensional case. Further, Sajid et al.[5] and Hayat et al.[6] considered the rotating flow over a shrinking surface. The steady boundary layer flow problems induced by a shrinking sheet can be found in [711] in different aspects. On the other hand, the unsteady case is described in papers by Fang et al.[12] and Ali et al.[13,14]. It is worth mentioning that dual solutions are also found in the papers by Fang [11], Fang et al.[12] and Ali et al.[14].
Recently, Nadeem and Hussain [15] solved analytically the problem of magnetohydrodynamic (MHD) flow of a viscous fluid on a nonlinear porous shrinking sheet using the homotopy analysis method and dual solutions were not reported. Hence, the present paper aims to obtain the dual solutions numerically for the problem considered in Nadeem and Hussain [15] for various controlling parameters and magnetic parameters.
2 Basic equations
Consider the steady twodimensional flow of an incompressible electrically conducting
fluid towards a nonlinear porous shrinking sheet. The magnetic field
where u and v are the velocity components along the x and y directions, respectively, ν is the kinematic viscosity, ρ is the fluid density and σ is the fluid electrical conductivity. The boundary conditions of Eqs. (1) and (2) are
where
We assume the magnetic Reynolds number is small, so that the induced magnetic field is negligible. Applying the following similarity transformations:
to Eqs. (1) and (2), we obtain the following ordinary differential equation:
subject to the boundary conditions
where primes denote differentiation with respect to η, while
are the wall mass transfer (suction) parameter, the magnetic parameter and the nondimensional (controlling) parameter, respectively.
The physical quantities of interest is the skin friction coefficient
where the shear stress
with μ being the dynamic viscosity. Using (5) and (10), we get
where
3 Results and discussion
Equation (6) subject to the boundary conditions (7) has been solved numerically using
the shooting method as described in the paper by Meade et al.[17]. This technique is an iterative algorithm which attempts to identify appropriate
initial conditions for a related initial value problem (IVP) that provides the solution
to the original boundary value problem (BVP). The results of the skin friction coefficient
Table 1
. Various values of
Figure 1 shows the variations of the skin friction coefficient
Figure 1
. Variation of the skin friction coefficient for different values ofβwhen
The variations of the skin friction coefficients with the suction parameter for
Figure 2
. Variation of the skin friction coefficient for different values ofMwhen
Figure 3
. Variation of the skin friction coefficient for different values ofMwhen
Figure 4
. Variation of the skin friction coefficient for different values ofMwhen
Figures 5 and 6 illustrate the dual velocity profiles for various β and M, respectively, with both figures satisfying the boundary conditions (7). This is to prove the dual nature of the present problem. From Figure 5, the boundary layer thickness increases with β. However, the boundary layer thickness decreases as M increases, as displayed in Figure 6. This phenomenon is due to the fact that M creates the Lorentz force which slows down the fluid flow, hence reducing the boundary layer thickness.
Figure 5
. Velocity profiles for different values ofβwhen
Figure 6
. Velocity profiles for different values ofMwhen
4 Conclusions
A study is performed for the problem of MHD flow of a viscous fluid on a nonlinear porous shrinking sheet. It is observed that the dual solutions existed only for positive values of the controlling parameter. In this study, we can conclude that the controlling parameter accelerated the boundary layer separation, however, the magnetic parameter delayed the boundary layer separation.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All authors have contributed their parts equally and have also read and approved the final manuscript.
Acknowledgements
The authors gratefully acknowledged the financial support received in the form of a FRGS research grant and a LRGS research grant (LRGS/TD/2011/UKM/ICT/03/02) from the Ministry of Higher Education, Malaysia, and DIP201231 from the Universiti Kebangsaan Malaysia.
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