# Alternative least‐squares finite element models of Navier‐Stokes equations for power‐law fluids Academic Article •
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### abstract

• Purpose - Most studies of power-law fluids are carried out using stress-based system of Navier-Stokes equations; and least-squares finite element models for vorticity-based equations of power-law fluids have not been explored yet. Also, there has been no study of the weak-form Galerkin formulation using the reduced integration penalty method (RIP) for power-law fluids. Based on these observations, the purpose of this paper is to fulfill the two-fold objective of formulating the least-squares finite element model for power-law fluids, and the weak-form RIP Galerkin model of power-law fluids, and compare it with the least-squares finite element model. Design/methodology/approach - For least-squares finite element model, the original governing partial differential equations are transformed into an equivalent first-order system by introducing additional independent variables, and then formulating the least-squares model based on the lower-order system. For RIP Galerkin model, the penalty function method is used to reformulate the original problem as a variational problem subjected to a constraint that is satisfied in a least-squares (i.e. approximate) sense. The advantage of the constrained problem is that the pressure variable does not appear in the formulation. Findings - The non-Newtonian fluids require higher-order polynomial approximation functions and higher-order Gaussian quadrature compared to Newtonian fluids. There is some tangible effect of linearization before and after minimization on the accuracy of the solution, which is more pronounced for lower power-law indices compared to higher power-law indices. The case of linearization before minimization converges at a faster rate compared to the case of linearization after minimization. There is slight locking that causes the matrices to be ill-conditioned especially for lower values of power-law indices. Also, the results obtained with RIP penalty model are equally good at higher values of penalty parameters. Originality/value - Vorticity-based least-squares finite element models are developed for power-law fluids and effects of linearizations are explored. Also, the weak-form RIP Galerkin model is developed. © 2011 Emerald Group Publishing Limited. All rights reserved.

### author list (cited authors)

• Vallala, V. P., Reddy, J. N., & Surana, K. S.

• 2

• October 2011