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- Asymmetry in transitional pipe flow of drag-reducing polymer solutionsPublication . Escudier, Marcel; Rosa, Sergio; Poole, RobNew experimental data are presented and discussed for fully developed pipe flow of shear-thinning, viscoelastic polymer solutions in the transitional regime between laminar and turbulent flow. The data confirm that such transitional flows exhibit significant departures from axisymmetry in contrast to the fully developed pipe flow of Newtonian fluids or both laminar and turbulent flows of such drag-reducing liquids. The azimuthal structure of the asymmetry is investigated together with its axial development and also the velocity fluctuation levels. These data do not lead to an explanation for the asymmetry but do suggest that the influence of the flow geometry both upstream and downstream can be ruled out.
- Pressure drop coefficient of laminar Newtonian flow in axisymmetric diffusersPublication . Rosa, Sergio; Pinho, Fernando T.The laminar flow of Newtonian fluids in axisymmetric diffusers has been numerically investigated to evaluate the pressure-loss coefficient as a function of Reynolds number, diffusion angle and expansion ratio. The numerical simulations were carried out with a finitevolume based code using non-orthogonal collocated grids and second order accurate differencing schemes to discretize all terms of the transport equations. The calculations were carried out for Reynolds numbers between 2 and 200, diffusion angles from 0 to 90 and expansion ratios of 1.5 and 2 and the data are presented in tabular form and as correlations. A simplified 1D theoretical analysis helped explain the various contributions to the loss coefficient and its difference relative to the reversible pressure variation due to differences between the actual and fully developed friction losses, distortions of the velocity profiles and pressure non-uniformity upstream and downstream of the expansion section.
- Assimetrias do escoamento de líquidos não-Newtonianos em regime de transiçãoPublication . Rosa, Sergio; Escudier, Marcel; Poole, RobEste trabalho apresentada e discute novos resultados experimentais obtidos em escoamentos no interior de condutas, usando fluidos não-Newtonianos em regime de transição, entre laminar e turbulento. Os dados confirmam que o escoamento de líquidos com redução de arrasto em regime de transição diverge significativamente, no que à simetria dos perfis de velocidade diz respeito, do escoamento de fluidos Newtonianos em todos os regimes. A estrutura da assimetria e a sua evolução ao longo do escoamento formam investigadas neste trabalho, assim como os níveis de flutuação da velocidade. Os resultados não conduziram de forma conclusiva à explicação da existência de assimetrias nos escoamentos em regime de transição e para fluidos não-Newtonianos, mas permitiram conclui que a geometria do escoamento, quer a jusante quer a montante, não produz qualquer influência sobre a assimetria dos perfis de velocidade.