Turbulence Transport in Rotor-Stator and Stator-Rotor Stages of Axial Flow Fans

Turbulence analysis in turbomachines is a complex task. The combination of different turbulence sources and transport mechanisms poses the question of determining adequate metrics to quantify turbulence levels and provide insight into the flow structure and its evolution. Apart from experimental measurement techniques, numerical techniques arise as a useful tool to characterize this type of flow, especially hybrid LES techniques that allow a highly accurate description of the transport of turbulent structures, while turbulence generation at solid boundaries is addressed using RANS schemes. In this chapter, recent developments concerning numerical simulation of rotor-stator and stator-rotor interactions in low-speed axial fans using LES techniques are presented. A post-processing framework is introduced to segregate the deterministic and turbulent components of the unsteady flow, allowing an accurate description of both phenomena. Hence, turbulent transport over the different stage rows of the axial fan can be accurately addressed. Following, LES capacities to simulate turbulence transport mechanisms such as breaking-up of turbulent eddies, stretching and dissipation of vorticity or identification and convection of coherent vortices are discussed. The ability of LES computations to disclose flow turbulence in rotor-stator environments at off-design conditions is specially illustrated

A Discussion on the Effective Ventilation Distance in Dead-End Tunnels

[EN] Forcing ventilation is the most widely used system to remove noxious gases from a working face during tunnel construction. This system creates a region near the face (dead zone), in which ventilation takes place by natural diffusion, rather than being directly swept by the air current. Despite the extensive use of this system, there is still a lack of parametrical studies discerning the main parameters affecting its formation as well as a correlation indicating their interrelation. With this aim in mind, computational fluid dynamics (CFDs) models were used to define the dead zone based on the airflow field patterns. The formation of counter vortices, which although maintain the movement of air hinder its renewal, allowed us to discuss the old paradigm of defining the dead zone as a very low air velocity zone. Moreover, further simulations using a model of air mixed with NO2 offered an idea of NO2 concentrations over time and distance to the face, allowing us to derive at a more realistic equation for the effective distance. The results given here confirm the degree of conservativism of present-day regulations and may assist engineers to improve ventilation efficiency in tunnels by modifying the duct end-to-face distanc

Optimización de una turbina de impulso radial para el aprovechamiento de la energía del oleaje

Esta tesis versa sobre la turbina de impulso radial, utilizada en centrales Oscillating Water Column (OWC) de aprovechamiento energético del oleaje. Este trabajo, donde se analiza con detalle del patrón de flujo mediante un modelo CFD, tiene como objetivo final desarrollar un diseño optimizado de este tipo de turbina. El modelo CFD permite predecir las prestaciones de la turbina, conocer el patrón de flujo y analizar la influencia de las holguras en el funcionamiento de la turbina. Gracias al modelo se han detectado en el diseño inicial importantes pérdidas asociadas a una incorrecta orientación de los elementos y a una elección no óptima de los perfiles de las aletas y de los álabes. Finalmente, se han elaborado unos criterios de diseño según los cuales se ha desarrollado un diseño alternativo que incorpora nuevos perfiles de álabe y de aletas. Gracias a estas modificaciones la turbina ha incrementado su rendimiento, cumpliendo así el objetivo principal de la tesis.Departamento de Ingeniería Energética y Fluidomecánic

Wiping Systems: Influence of the Surface Tension in Water Film Rupture

Wiping system are widely employed in industrial processes to remove liquid residue from the final product. Therefore, the performance of the impingement of a gas jet upon a liquid surface or molten bath is relevant in many industrial and metallurgical processes. This work is focused on wiping systems used in steel cold rolling, where a system composed of air jets impinging on the steel strip should remove the thin film of lubricant emulsion coming from the rolling bite. In the bibliography there are references of analytical cases of reduction of coating thickness by means of an air jet, such as galvanizing processes, which do not take into account surface tension. In the case of drying systems film rupture exists. A lot of variables are implied in the film rupture theory. Upon all of them the most important variable is the surface tension. The aim of this work is to study the influence of surface tension in film rupture. For this reason, a model of a jet wiping a film of water upon a strip is developed with and without surface tension

A discussion on the effective ventilation distance in dead-end tunnels

M.G.-D. was supported by the Spanish "Ministerio de Educacion, Cultura y Deporte" within the " FPU" Program (grant number FPU15/04375). C.M.G. was supported by the Spanish " Ministerio de Educacion Cultura y Deporte" within the " Doctorados Industriales" Program (grant number DI-17-09596)

Optimization and experimental tests of a centrifugal turbine for an OWC device equipped with a twin turbines configuration

Radial turbines are suitable for OWC devices with twin turbine configuration. The performance of radial turbines when working as backflow preventer is good. Performance of previous models clearly surpassed, both direct and reverse mode. Leaking flow through the turbine not producing energy is lower than 20%. The non-steady efficiency catches up with that achieved by axial turbines

Deterministic decomposition of the unsteady flow in a unidirectional axial turbine for OWC plant

ASME. International Conference on Ocean, Offshore and Arctic Engineering (37th, 2018, Madrid, Spain