Manuel A. Alves

Learn More
Using a numerical technique we demonstrate that the flow of the simplest differential viscoelastic fluid model (i.e., the upper-convected Maxwell model) goes through a bifurcation to a steady asymmetric state when flowing in a perfectly symmetric "cross-slot" geometry. We show that this asymmetry is purely elastic in nature and that the effect of inertia is(More)
— The objective of this study was to illustrate how different methods of obtaining the Radar Cross Section (RCS) of an object may produce different results. RCS diagrams of a metallic airplane model (length, 0.64 m) were obtained in an anechoic chamber, with a Lab-Volt RCS system, and simulated with a simulation software. The measurements and simulations(More)
financial support provided under program POCI2010 by FCT and FEDER (project POCI/EQU/59256/2004) We present a detailed numerical study of the flow of a Newtonian fluid through microrheometric devices featuring a sudden contraction-expansion. This flow configuration is typically used to generate extensional deformations and high strain rates. The excess(More)
A precision-machined cross-slot flow geometry with a shape that has been optimized by numerical simulation of the fluid kinematics is fabricated and used to measure the extensional viscosity of a dilute polymer solution. Full-field birefringence microscopy is used to monitor the evolution and growth of macromolecular anisotropy along the stagnation point(More)
We investigate the stability of steady planar stagnation flows of a dilute polyethylene oxide (PEO) solution using T-shaped microchannels. The precise flow rate control and well-defined geometries achievable with microfluidic fabrication technologies enable us to make detailed observations of the onset of elastically-driven flow asymmetries in steady flows(More)
Wormlike micellar surfactant solutions are encountered in a wide variety of important applications, including enhanced oil recovery and ink-jet printing, in which the fluids are subjected to high extensional strain rates. In this contribution we present an experimental investigation of the flow of a model wormlike micellar solution (cetyl pyridinium(More)
a We determine both experimentally and numerically the onset of elastic flow instabilities in viscoelastic polymer solutions with different levels of shear thinning. Previous experiments realized in microfluidic serpentine channels using dilute polymeric solutions showed that the onset of elastic instabilities strongly depends on the channel curvature. The(More)
A biofouling simulation system consisting of a flow cell and a recirculation tank was used. The fluid circulates at a flow rate of 350 L· h⁻¹ in a semicircular flow cell with hydraulic diameter of 18.3 mm, corresponding to an average velocity of 0.275 m· s⁻¹. Using computational fluid dynamics for flow simulation, an average wall shear stress of 0.4 Pa was(More)