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An improved spectral homotopy analysis method for solving boundary layer problems


This article presents an improved spectral-homotopy analysis method (ISHAM) for solving nonlinear differential equations. The implementation of this new technique is shown by solving the Falkner-Skan and magnetohydrodynamic boundary layer problems. The results obtained are compared to numerical solutions in the literature and MATLAB's bvp4c solver. The results show that the ISHAM converges faster and gives accurate results.


Boundary layer flow problems have wide applications in fluid mechanics. In this article, we propose an improved spectral-homotopy analysis method (ISHAM) for solving general boundary layer problems. Three boundary layer problems are considered and solved in this study using the novel technique. The first problem considered is the classical two-point nonlinear boundary value Blasius problem which models viscous fluid flow over a semi-infinite flat plate. Although solutions for this problem had been obtained as far back as 1908 by Blasius [1], the problem is still of great interest to many researchers as can be seen from the several recent studies [25].

The second problem considered in this article is the third-order nonlinear Falkner-Skan equation. The Falkner-Skan boundary layer equation has been studied by several researchers from as early as 1931 [6]. More recent studies of the solutions of the The Falkner-Skan equation include those of Harries et al. [7], Pade [8] and Pantokratoras [9]. The third problem considered is magnetohy-drodynamic (MHD) boundary layer flow. Such boundary layer problems arise in the study of the flow of electrically conducting fluids such as liquid metal. Owing to its many applications such as power generators, flow meters, and the cooling of reactors, MHD flow has been studied by many researchers, for example [10, 11].

Owing to the nonlinearity of equations that describe most engineering and science phenomena, many authors traditionally resort to numerical methods such as finite difference methods [12], Runge-Kutta methods [13], finite element methods [14] and spectral methods [4] to solve the governing equations. However, in recent years, several analytical or semi-analytical methods have been proposed and used to find solutions to most nonlinear equations. These methods include the Adomian decomposition method [1517], differential transform method [18], variational iteration method [19], homotopy analysis method (HAM) [2023], and the spectral-homotopy analysis (SHAM) (see Motsa et al. [24, 25]) which sought to remove some of the perceived limitations of the HAM. More recently, successive linearization method [2628], has been used successfully to solve nonlinear equations that govern the flow of fluids in bounded domains.

In this article, boundary layer equations are solved using the ISHAM. The ISHAM is a modified version of the SHAM [24, 25]. One strength of the SHAM is that it removes restrictions of the HAM such as the requirement for the solution to conform to the so-called rule of solution expression and the rule of coefficient ergodicity. Also, the SHAM inherits the strengths of the HAM, for example, it does not depend on the existence of a small parameter in the equation to be solved, it avoids discretization, and the solution obtained is in terms of an auxiliary parameter ħ which can conveniently be chosen to determine the convergence rate of the solution.

Mathematical formulation

We consider the general nonlinear third-order boundary value problem


subject to the boundary conditions


where c i , b j (i = 1, ..., 4 j = 1, 2, 3) are constants.

Equation 2.1 can be solved easily using methods such as the HAM and the SHAM. In each of these methods, an initial approximation f0(η) is sought, which satisfies the boundary conditions. The speed of convergence of the method depends on whether f0(η) is a good approximation of f (η) or not. The approach proposed here seeks to find an optimal initial approximation f0 that would lead to faster convergence of the method to the true solution. We thus first seek to improve the initial approximation that is used later in the SHAM to solve the governing nonlinear equation.

We assume that the solution f(η) may be expanded as an infinite sum:


where f i 's are unknown functions whose solutions are obtained using the SHAM at the i th iteration and f n , (n ≥ 1) are known from previous iterations. The algorithm starts with the initial approximation f0(η) which is chosen to satisfy the boundary conditions (2.2). An appropriate initial guess is


Substituting (2.3) in the governing equation (2.1-2.2) gives


subject to the boundary conditions


where the coefficient parameters ak,i-1, (k = 1, ..., 3) and ri-1are defined as


Starting from the initial approximation (2.4), the subsequent solutions f i (i ≥ 1) are obtained by recursively solving Equation 2.5 using the SHAM, [24, 25]. To find the solutions of Equation 2.5, we begin by defining the following linear operator:


where q 0[1] is the embedding parameter, and F i (η; q) is an unknown function.

The zeroth-order deformation equation is given by


where ħ is the non-zero convergence controlling auxiliary parameter and is a nonlinear operator given by


Differentiating (2.10) m times with respect to q and then setting q = 0, and finally dividing the resulting equations by m! yield the m th-order deformation equations:


subject to the boundary conditions




The initial approximation fi,0that is used in the higher-order equations (2.12) is obtained on solving the linear part of Equation 2.5 which is given by


subject to the boundary conditions:


Since the coefficient parameters and the right-hand side of Equation 2.15 for i = 1, 2, 3, ... are known (from previous iterations), the equation can easily be solved using numerical methods such as finite differences, finite elements, Runge-Kutta-based shooting methods or collocation methods. In this article, Equation 2.15 are solved using the Chebyshev spectral collocation method. The method (see, for example, [2931]), is based on the Chebyshev polynomials defined on the interval [-1, 1] by


To implement the method, the physical region [0, ∞) is transformed into the region [-1, 1] using the domain truncation technique whereby the problem is solved in the interval [0, L] instead of [0, ∞). This leads to the mapping


where L is the scaling parameter used to invoke the boundary condition at infinity. We use the popular Gauss-Lobatto collocation points [29, 31] to define the Chebyshev nodes in [-1, 1], namely:


where N is the number of collocation points. The variable fi,0is approximated by the interpolating polynomial in terms of its values at each of the collocation points by employing the truncated Chebyshev series of the form:


where T k is the k th Chebyshev polynomial. Derivatives of the variables at the collocation points may be represented by


where s is the order of differentiation and , with being the Chebyshev spectral differentiation matrix (see, for example [29, 31]) whose entries are defined as


Substituting Equations 2.20-2.21 in 2.15-2.16 gives


subject to




In the above definitions, T stands for transpose and ak,i-1(k = 1, 2, 3) denotes a diagonal matrix of size (N + 1) × (N + 1). The boundary condition f i (ξ N ) = 0 is implemented by deleting last row and last column of Ai-1, and deleting the last rows of Fi,0and Ri-1. The derivative boundary conditions in (2.24) are then imposed on the resulting first row and last row of Ai-1and setting the first and last rows of Fi,0and Ri-1to be zero. The solutions for fi.0(ξ) are then obtained from soloving


In a similar manner, applying the Chebyshev spectral transformation on the higher order deformation equations (2.12)-(2.13) gives


subject to the boundary conditions


where Ai-1and Ri-1, are as defined in (2.25) and (2.27), respectively, and


To implement the boundary condition fi,m(ξ N ) = 0, we delete the last rows of Pi,m-1and Ri-1and delete the last row and the last column of Ai-1in (2.29). The other boundary conditions in (2.30) are imposed on the first and the last rows of the modified Ai-1matrix on the left side of the equal sign in (2.29). The first and the last rows of the modified Ai-1matrix on the right side of the equal sign in (2.29) are then set to be zero. This results in the following recursive formula for m ≥ 1:


where Ãi-1is the modified matrix Ai-1after incorporating the boundary conditions (2.30). Thus, starting from the initial approximation, which is obtained from (2.28), higher-order approximations fi,m(ξ) for m ≥ 1, can be obtained through the recursive formula (2.33).

The solutions for f i are then generated using the solutions for fi, mas follows:


The [i, m] approximate solution for f (η) is then obtained by substituting f i (obtained from 2.34) in equation 2.3.

Results and discussion

Table 1 shows the values of f" (0) at different orders [i, m] of the ISHAM approximation for the Blasius boundary layer flow when L = 30, ħ = -1 and N = 80. It is worth noting here that the numerical solution given by Howarth [32] is f" (0) = 0.332057, while the numerical result by the Matlab bvp4c routine is f" (0) = 0.33205734. Asaithambi [33] found this number correct to nine decimal positions as 0.332057336. It is evident that the ISHAM converges to the numerical result at orders [3,1] and [2,2]. Moreover, Table 1 shows that the ISHAM solution converges to the accurate solution of Howarth and the bvp4c result faster than the original SHAM results of which are those given in the first row of Table 1 (for the case when i = 1).

Table 1 Order [i, m] ISHAM approximate results for f" (0) of the Blasius boundary layer flow (Example 1) using L = 30, ħ = -1 and N = 80

In general, at order [i, m], i is the number of improvements of the initial approximation f0(η) for f(η), and m is the number of improvements of the initial guess f q ,0(η); q = 1, 2, ..., i, for each application of the ISHAM. Table 2 gives a sense of the convergence rate of the ISHAM when compared with the numerical method for the Blasius problem at different values of η. In all the instances, convergence of the ISHAM is achieved at the second order.

Table 2 Comparison between the [m, m] ISHAM results and the bvp4c numerical results for the velocity pro le f' (η) at selected values of η for the Blasius boundary layer flow (Example 1) using L = 30, ħ = -1 and N = 200

Table 3 gives the values of f" (0) obtained used the ISHAM and the numerical method for various values of β for the Falkner-Skan boundary layer problem. Full convergence is again achieved at order [2,2] for all the parameter values.

Table 3 Order [m, m] ISHAM approximate results for f" (0) of the Falkner-Skan boundary layer flow (Example 2) using L = 30, ħ = -1 and N = 80

For the MHD boundary layer problem, Tables 4 and 5 illustrate the exact and approximate values of f' (η) and f" (0) at different values of η and the magnetic parameter M, respectively. The absolute errors in the approximations are also given. The tables show that the ISHAM converges rapidly with marginal or no errors after order [2,2].

Table 4 Order [m, m] ISHAM approximate results for the velocity profile f' (η) of the MHD boundary layer flow (Example 3) when M = 10 using L = 10, ħ = -1 and N = 200
Table 5 Order [m, m] ISHAM approximate results for f" (η) of the MHD boundary layer flow (Example 3) for different values of M using L = 10, ħ = -1 and N = 200


In this article, we have proposed an ISHAM for solving general nonlinear differential equations. This novel technique was compared against both numerical approximations and the MATLAB bvp4c routine for solving Falkner-Skan and MHD boundary layer problems. The results demonstrate the relatively more rapid convergence of the ISHAM, and they show that the ISHAM is highly accurate.



homotopy analysis method


improved spectral-homotopy analysis method




spectral-homotopy analysis.


  1. Blasius H: Grenzschichten in Flussigkeiten mit kleiner Reibung. Z Math Phys 1908, 56: 1-37.

    Google Scholar 

  2. Ahmad F, Al-Barakati WH: An analytic solution of the Blasius problem. Commun Nonlinear Sci Numer Simul 2009, 14: 1020-1024.

    MathSciNet  Google Scholar 

  3. Alizadeh-Pahlavan A, Borjian-Boroujeni S: On the analytic solution of viscous fluid flow past a flat plate. Phys Lett A 2008, 372: 3678-3682. 10.1016/j.physleta.2008.02.050

    Article  Google Scholar 

  4. Parand K, Shahini M, Dehghan M: Solution of a laminar boundary layer flow via a numerical method. Commun Nonlinear Sci Numer Simulat 2010, 15: 360-367. 10.1016/j.cnsns.2009.04.007

    Article  Google Scholar 

  5. Yun BI: Intuitive approach to the approximate analytical solution for the Blasius problem. Appl Math Comput 2009, 208: 156-164. 10.1016/j.amc.2008.11.028

    Article  MathSciNet  Google Scholar 

  6. Falkner VM, Skan SW: Some approximate solutions of the boundary layer equations. Philos Mag 1931, 12: 865-896.

    Article  Google Scholar 

  7. Harris SD, Ingham DB, Pop I: Unsteady heat transfer in impulsive Falkner-Skan flows: constant wall temperature case. Eur J Mech B 2002, 21: 447-468. 10.1016/S0997-7546(02)01193-7

    Article  MathSciNet  Google Scholar 

  8. Padé O: On the solution of Falkner-Skan equations. J Math Anal Appl 2003, 285: 264-274. 10.1016/S0022-247X(03)00402-5

    Article  MathSciNet  Google Scholar 

  9. Pantokratoras A: The Falkner-Skan flow with constant wall temperature and variable viscosity. Int J Thermal Sci 2006, 45: 378-389. 10.1016/j.ijthermalsci.2005.06.004

    Article  Google Scholar 

  10. Rashidi MM: The modified differential transform method for solving MHD boundary-layer equations. Comput Phys Commun 2009, 180: 2210-2217. 10.1016/j.cpc.2009.06.029

    Article  MathSciNet  Google Scholar 

  11. Parand K, Rezai AR, Ghaderi SM: An approximate solution of the MHD Falkner-Skan flow by Hermite functions pseudospectral method. Commun Nonlinear Sci Numer Simulat 2010.

    Google Scholar 

  12. Asaithambi A: A second-order finite-difference method for the Falkner-Skan equation. Appl Math Comput 2004, 156: 779-786. 10.1016/j.amc.2003.06.020

    Article  MathSciNet  Google Scholar 

  13. Cortell R: Numerical solutions of the classical Blasius flat-plate problem. Appl Math Comput 2005, 170: 706-710. 10.1016/j.amc.2004.12.037

    Article  MathSciNet  Google Scholar 

  14. Asaithambi A: Numerical solution of the Falkner-Skan equation using piecewise linear functions. Appl Math Comput 2004, 159: 267-273. 10.1016/j.amc.2003.10.047

    Article  MathSciNet  Google Scholar 

  15. Elgazery NS: Numerical solution for the Falkner-Skan equation. Chaos Soliton Fract 2008, 35: 738-746. 10.1016/j.chaos.2006.05.040

    Article  Google Scholar 

  16. Wang L: A new algorithm for solving classical Blasius equation. Appl Math Comput 2004, 157: 1-9. 10.1016/j.amc.2003.06.011

    Article  MathSciNet  Google Scholar 

  17. Abbasbandy S: A numerical solution of Blasius equation by Adomian's decomposition method and comparison with homotopy perturbation method. Chaos Soliton Fract 2007, 31: 257-260. 10.1016/j.chaos.2005.10.071

    Article  Google Scholar 

  18. Kuo B: Heat analysis for the Falkner-Skan wedge flow by the differential transformation method. Int J Heat Mass Transfer 2005, 48: 5036-5046. 10.1016/j.ijheatmasstransfer.2003.10.046

    Article  Google Scholar 

  19. Wazwaz A: The variational iteration method for solving two forms of Blasius equation on a half-infinite domain. Appl Math Comput 2007, 188: 485-491. 10.1016/j.amc.2006.10.009

    Article  MathSciNet  Google Scholar 

  20. Liao SJ: Beyond Perturbation: Introduction to Homotopy Analysis Method. Chapman & Hall/CRC Press; 2003.

    Chapter  Google Scholar 

  21. Yao B, Chen J: A new analytical solution branch for the Blasius equation with a shrinking sheet. Appl Math Comput 2009, 215: 1146-1153. 10.1016/j.amc.2009.06.057

    Article  MathSciNet  Google Scholar 

  22. Yao B, Chen J: Series solution to the Falkner-Skan equation with stretching boundary. Appl Math Comput 2009, 215: 1146-1153. 10.1016/j.amc.2009.06.057

    Article  MathSciNet  Google Scholar 

  23. Yao B: Approximate analytical solution to the Falkner-Skan wedge flow with the permeable wall of uniform suction. Commun Nonlinear Sci Numer Simulat 2009, 14: 3320-3326. 10.1016/j.cnsns.2009.01.014

    Article  Google Scholar 

  24. Motsa SS, Sibanda P, Shateyi S: A new spectral-homotopy analysis method for solving a nonlinear second order BVP. Commun Nonlinear Sci Numer Simulat 2010, 15: 2293-2302. 10.1016/j.cnsns.2009.09.019

    Article  MathSciNet  Google Scholar 

  25. Motsa SS, Sibanda P, Awad FG, Shateyi S: A new spectral-homotopy analysis method for the MHD Jeffery-Hamel problem. Comput Fluids 2010, 39: 1219-1225. 10.1016/j.compfluid.2010.03.004

    Article  MathSciNet  Google Scholar 

  26. Makukula Z, Motsa SS, Sibanda P: On a new solution for the viscoelastic squeezing flow between two parallel plates. J Adv Res Appl Math 2010, 2(4):31-38. 10.5373/jaram.455.060310

    Article  MathSciNet  Google Scholar 

  27. Makukula ZG, Sibanda P, Motsa SS: A novel numerical technique for two-dimensional laminar flow between two moving porous walls. Math Problems Eng 2010, 15: Article ID 528956.

    MathSciNet  Google Scholar 

  28. Shateyi S, Motsa SS: Variable viscosity on magnetohydrodynamic fluid flow and heat transfer over an unsteady stretching surface with Hall effect. Boundary Value Problems 2010, 2010: 1-20.

    Article  MathSciNet  Google Scholar 

  29. Canuto C, Hussaini MY, Quarteroni A, Zang TA: Spectral Methods in Fluid Dynamics. Springer-Verlag, Berlin; 1988.

    Chapter  Google Scholar 

  30. Don WS, Solomonoff A: Accuracy and speed in computing the Chebyshev Collocation Derivative. SIAM J Sci Comput 1995, 16(6):1253-1268. 10.1137/0916073

    Article  MathSciNet  Google Scholar 

  31. Trefethen LN: Spectral Methods in MATLAB. SIAM 2000.

    Google Scholar 

  32. Howarth L: On the solution of the laminar boundary layer equations. Proc R Soc Lond A 1938, 164: 547-579. 10.1098/rspa.1938.0037

    Article  Google Scholar 

  33. Asaithambi A: Solution of the Falkne-Skan equation by recursive evaluation of Taylor coefficients. J Comput Appl Math 2005, 176: 203-14. 10.1016/

    Article  MathSciNet  Google Scholar 

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The authors wish to acknowledge financial support from the University of Swaziland, University of KwaZulu-Natal, University of Venda, and the National Research Foundation (NRF).

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Correspondence to Stanford Shateyi.

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The authors declare that they have no competing interests.

Authors' contributions

SSM developed the Matlab codes and generated the results. GTM and PS conceived of the study and formulated the problem. SS participated in the analysis of the results and manuscript coordination. All authors typed, read and approved the final manuscript.

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Motsa, S.S., Marewo, G.T., Sibanda, P. et al. An improved spectral homotopy analysis method for solving boundary layer problems. Bound Value Probl 2011, 3 (2011).

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  • Falkner-Skan flow
  • MHD flow
  • improved spectral-homotopy analysis method