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Research Papers

Convective Eigenvalue Problems for Convergence Enhancement of Eigenfunction Expansions in Convection–Diffusion Problems

[+] Author and Article Information
Renato M. Cotta

LabMEMS—Laboratory of Nano &
Microfluidics and Microsystems,
Mechanical Engineering
Department—PEM, POLI/COPPE,
Rio de Janeiro 21945-970, Brazil;
Nanoengineering
Department—PENT, COPPE,
Federal University of Rio de Janeiro, UFRJ,
Cx. Postal 68503—Cidade Universitária,
Rio de Janeiro 21945-970, Brazil
e-mail: cotta@mecanica.coppe.ufrj.br

Carolina P. Naveira-Cotta

LabMEMS—Laboratory of Nano &
Microfluidics and Microsystems,
Mechanical Engineering
Department—PEM, POLI/COPPE,
Rio de Janeiro 21945-970, Brazil;
Nanoengineering
Department—PENT, COPPE,
Federal University of Rio de Janeiro, UFRJ,
Cx. Postal 68503—Cidade Universitária,
Rio de Janeiro 21945-970, Brazil

Diego C. Knupp

Mechanical Engineering Department,
Polytechnic Institute,
State University of Rio de Janeiro,
IPRJ/UERJ,
Nova Friburgo, RJ 28625-570, Brazil

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received December 18, 2016; final manuscript received June 27, 2017; published online September 13, 2017. Assoc. Editor: Pedro Mago.

J. Thermal Sci. Eng. Appl 10(2), 021009 (Sep 13, 2017) (12 pages) Paper No: TSEA-16-1378; doi: 10.1115/1.4037576 History: Received December 18, 2016; Revised June 27, 2017

The present work considers the application of the generalized integral transform technique (GITT) in the solution of a class of linear or nonlinear convection–diffusion problems, by fully or partially incorporating the convective effects into the chosen eigenvalue problem that forms the basis of the proposed eigenfunction expansion. The aim is to improve convergence behavior of the eigenfunction expansions, especially in the case of formulations with significant convective effects, by simultaneously accounting for the relative importance of convective and diffusive effects within the eigenfunctions themselves, in comparison against the more traditional GITT solution path, which adopts a purely diffusive eigenvalue problem, and the convective effects are fully incorporated into the problem source term. After identifying a characteristic convective operator, and through a straightforward algebraic transformation of the original convection–diffusion problem, basically by redefining the coefficients associated with the transient and diffusive terms, the characteristic convective term is merged into a generalized diffusion operator with a space-variable diffusion coefficient. The generalized diffusion problem then naturally leads to the eigenvalue problem to be chosen in proposing the eigenfunction expansion for the linear situation, as well as for the appropriate linearized version in the case of a nonlinear application. The resulting eigenvalue problem with space variable coefficients is then solved through the GITT itself, yielding the corresponding algebraic eigenvalue problem, upon selection of a simple auxiliary eigenvalue problem of known analytical solution. The GITT is also employed in the solution of the generalized diffusion problem, and the resulting transformed ordinary differential equations (ODE) system is solved either analytically, for the linear case, or numerically, for the general nonlinear formulation. The developed methodology is illustrated for linear and nonlinear applications, both in one-dimensional (1D) and multidimensional formulations, as represented by test cases based on Burgers' equation.

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Grahic Jump Location
Fig. 1

(a) and (b) Convergence behavior of T(x,t) for nonlinear 1D Burgers equation at t = 0.05 for truncation orders I = 4, 8, 12, 16, and 20: (a) convective basis and (b) diffusive basis

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