J.G. Barbosa-Saldaña

Flow Over a Three-Dimensional Horizontal Forward-Facing Step

A numerical code based on a finite volume technique was developed to simulate laminar flow over a three-dimensional horizontal forward-facing step. Pressure and velocity fields were linked by the SIMPLE algorithm. A rectangular channel encloses the forward-facing step such that the expansion ratio (ER) and the aspect ratio (AR) are equal to two and four, respectively. The channel total length in the stream-wise direction is equal to sixty times the step height and the step edge is located at a distance equal to twenty times the step height downstream of the channel inlet. At the channel inlet flow is considered to be fully developed and three-dimensional. Effect of variation of Reynolds number (Re = 100, 200, 400, and 800) on locations of the reattachment line, the separation line, velocity profiles at different planes, and spanwise averaged Nusselt numbers are discussed.

RANS simulations of the U and V grooves effect in the subcritical flow over four rotated circular cylinders

This paper presents a CFD study about the effect of the V and U grooves in the flow over four cylinders in diamond shape configuration at subcritical flow conditions (Re = 41000). The k-ε Realizable turbulence model was implemented to fully structured hexahedral grids with near-wall refinements. Results showed that the numerical model was able to reproduce the impinging flow pattern and the repulsive forces present in the lateral cylinders of the smooth cylinder array. As a consequence of the flow alignment induced by the grooves, a jet-flow is formed between the lateral cylinders, which could cause an important vortex induced vibration effect especially in the rear cylinder. The magnitudes of the shear stresses at the valleys and peaks for the V grooved cylinders were lower than those of the U grooved cylinders, but the separation points were delayed due the U grooves presence. It is discussed the presence of a blowing effect caused by counter-rotating eddies located near the grooves peaks that cause a decrease of the shear stresses in the valleys, and promote them at the peaks.

Comportamiento Hidrodinámico y Térmico del Flujo Gas- Sólido en un Reactor de Tubo Vertical (Riser) del Proceso de Craqueo Catalítico (FCC) con dos Salidas Laterales Asimétricas

Resumen En este trabajo se realiza la simulacion numerica en 2D del comportamiento hidrodinamico y termico del flujo gas-solido en un reactor industrial (riser) con dos salidas colocadas asimetricamente, utilizando un modelo de la Dinamica de Fluidos Computacional. El sistema se considera adiabatico y el modelo del sistema se resuelve por una aproximacion Euleriana transitoria y la Teoria Cinetica del Flujo Granular (KTGF, Kinetic Theory for Granular Flow). Como modelo de arrastre se utiliza la minimizacion multiescala de la energia (EMMS, Energy Minimization Multi-Scale). Las variables que se analizan son la distribucion de densidad, la distribucion de velocidades, la distribucion del flujo masico, y los perfiles de temperatura de la fase solida, a varias alturas del riser. Los resultados de este trabajo se comparan con los obtenidos anteriormente para una configuracion de salidas simetricas. El modelo predice adecuadamente la presencia de tres zonas de concentracion y velocidad de solidos, asi como la formacion del patron de flujo anular esperado en el riser.

Numerical Simulation of Flow Behavior within a Venturi Scrubber

The present work details the three-dimensional numerical simulation of single-phase and two-phase flow (air-water) in a venturi scrubber with an inlet and throat diameters of 250 and 122.5 mm, respectively. The dimensions and operating parameters correspond to industrial applications. The mass flow rate conditions were 0.483 kg/s, 0.736 kg/s, 0.861 kg/s, and 0.987 kg/s for the gas only simulation; the mass flow rate for the liquid was 0.013 kg/s and 0.038 kg/s. The gas flow was simulated in five geometries with different converging and diverging angles while the two-phase flow was only simulated for one geometry. The results obtained were validated with experimental data obtained by other researchers. The results show that the pressure drop depends significantly on the gas flow rate and that water flow rate does not have significant effects neither on the pressure drop nor on the fluid maximum velocity within the scrubber.

Numerical Simulation of the Subcritical Flow Over a Circular Cylinder With “U” and “V” Grooves

In this paper the comparative results of three numerical simulations of the subcritical turbulent flow over a circular cylinder (Re = 140,000) for the cases of a “U” grooved cylinder, a smooth cylinder, and a “V” grooved cylinder are presented. Due to the high resolution capabilities of the LES model, it was preferred over the RANS or URANS turbulence models. The simulation was carried out using the commercial CFD code ANSYS FLUENT V.12.0. The grid sizes were: 2.6 million cells for the smooth cylinder, and 14.5 and 13 million for the “U” grooved and “V” grooved cylinders respectively. In order to improve the quality of the solutions, the grids were structured and composed of hexahedral cells. Due to the requirements of the LES technique, the lower y+ values obtained were below 5. With the aim of capture the non-steady characteristics of this kind of flows, the simulations were performed over 8 vortex shedding cycles. Although the cross sections of the V and U grooves have almost the same shape, the resulting flow structures and calculated quantities such as the separation point, turbulent intensity in the normal and streamwise direction and recirculating bubble length were different for both cases. Apparently, the flow configuration resulted from the V grooves is similar to the smooth cylinder flow, being the U grooved cylinder flow different from both of them. This could be related to the drag reduction of about 27% obtained for the U grooved cylinder flow For the V grooved cylinder flow, the obtained drag presented an increase of about 7%.© 2013 ASME

Experimental Investigation of Friction Reduction in Transport of Fluids Using Surfactants

This paper presents the results of the influence of surfactants in reducing friction while driving fluid in pipes. Experimental research was conducted with water-surfactant mixtures which were tested three types of these additives: anionic, cationic and nonionic surfactants. Was designed and built an experimental facility in which the test area was acrylic pipe with an inner diameter of D = 19 mm and a length of 300 D. The concentrations of surfactants in the mixtures were 150, 250, 500, 750 and 1000 ppm, added according to a pilot program that took into account the amount and type of additive added in different liquid mass fluxes. Pressure losses were compared against those obtained when flow is the same water flows through the installation. The results obtained show a reduction of up to 43.9% of the friction which is achieved with a Re = 11243 and surfactant concentrations of 250 ppm (cetyl trimethyl chloride ammonium), to which was added as a stabilizer for the micro structure of the surfactant, sodium salicylate, which applies only to the cationic type surfactants. The results are promising but left to study such issues as: the injection and recovery of surfactant, more efficient mixing, the mechanisms that lead to a reduction of friction and the effect of temperature among others.Copyright

Análisis Numérico de la Convección Mixta en un Conducto Horizontal de Sección Rectangular Tridimensional que Encierra un Escalón

Laminar mixed convection over a backward-facing step is studied and presented in this work. A finite volume discretization technique is used to solve the momentum and energy equations. The SIMPLE algorithm is used to link the pressure distribution and velocity field inside the computational domain. The buoyancy forces affecting the velocity and temperature distributions are simulated for constant air flow and constant Reynolds number (Re=200) for a mixed convective flow (Ri=3) and the results are compared with those of pure force convective flow (Ri=0). The results indicate that the re-circulation zones at the vicinity of the back step are reduced if the buoyancy effects are considered. It is concluded that the flow is highly tridimensional.