Francisco Castro-Ruiz

An isothermal analysis of curved-vane and flat-vane swirlers for burners

Purpose – One current trend in burner technology is to obtain high efficiency while keeping low levels of NOx emissions. A swirling flow in combustion ensures a fixed position of a compact flame. Therefore, it is necessary to design efficient swirlers. Flow patterns are simulated for the different swirl devices proposed in this work. Two axial-swirlers are studied: one based on curve-vanes consisting of a straight line with an arc of a circle as the trailing edge and the other is the common flat-vanes. The purpose of this paper is to assess the accuracy of different swirl generators using a well-known benchmark test case. Design/methodology/approach – This work deals with modelling the swirler using two approaches: the general purpose Computational fluid dynamics (CFD) solver Ansys-Fluent® and the suite of libraries OpenFOAM® to solve the Reynolds Averaged Navier Stokes equations, showing there is a slight deviation between both approaches. Their performance involves analyzing not only the Swirl number bu...

Implicit les applied to isothermal swirling coaxial jets

This work is devoted to the analysis of the interaction of two coaxial jet with swirling flow using Large Eddy Simulation methodology to reproduce the case of Roback and Johnson. The eight - flat - vanes in the annular nozzle are the precursor of the swirling annular jet with high swirl number. An implicit LES model was used, this model uses mesh size as filter width so no sub-grid model is required. It is the numerical error who plays the role of dissipative part of the stress tensor in the sub-mesh. Mesh prerequisites are Ay+ = 1 and uniform hexahedral mesh. The resolution scheme used is a Total Variation Diminishing (TVD) with coefficients looking for good precision. PISO is the pressure-velocity coupling used. Besides, multigrid resolution improves the performance towards the full convergence. Influence of the swirl number on the flow pattern is analyzed. Also the impact of conical diffuser on the mixing is presented. (Less)

Swirl influence on mixing and reactive flows

The interaction of two confined coaxial jets has been studied using Computational Fluid Dynamics. Annular jet flows over 8 flat blade swirl generator. Numerical simulation uses RNG k- ϵ turbulence model. These models are suitable for turbulent swirl dominated flows. Intermediate swirl injector has been simulated and the flow patterns for non-reactive and reactive cases are contrasted. Low swirling injectors do not promote the fluid to turn over near the center of the chamber, resulting larger mixing zones with weak gradients. Whereas large swirling flows promote the formation of an Inner Recirculation Zone that is a precursor of higher gradients. Probability Density Function is selected as combustion model. High swirl numbers let fix the location of the reactive zone.

Influence of Flow Swirling on the Aerothermodynamic Behaviour of Flames

The present work focuses on the numerical simulation of diffusive flames in a confined high-swirl burner. Navier–Stokes equations expressed for a time-dependent, compressible, and three-dimensional flow with finite-rate kinetics are solved for lean methane/air mixtures. A simplified mechanism is used to model the combustion. Non-reactive and reactive cases are contrasted for a swirl number of 0.95. Three flames for swirl numbers of 0, 0.6, and 0.95 are analyzed. In swirling flows, the inner recirculation zone is mainly composed of reaction products, which help in ignition of the incoming fuel. Moreover, the forward stagnation point plays an important role, leading to an azimuthal deflection of the flame front.

Numerical Modeling of Vertical Axis Wind Turbines

This paper aims to predict the performance of Vertical Axis Wind Turbine (VAWT), hence the modeling of kinetic energy extraction from wind and its conversion to mechanical energy at the rotor axis, is carried out. The H-type Darrieus turbine consists of three straight blades with shape of aerofoil attached to a rotating vertical shaft. The criterion on the selection of this kind of turbines, despite its reduced efficiency, is the easy manufacture in workshops.A parametric study has been carried out to analyze the camber effect on the non dimensional curves of power coefficient so that the self starting features as well as the range of tip speed ratio of operation could be predicted.Copyright

Diffuser Influence on the Mixing of Coaxial Swirling Jets

Numerical results depicting the effects of diffusers on confined isothermal high-swirl jets are presented. The aim is analyze the mixing between a non-swirling inner jet (natural gas) and a swirling annular jet (primary air). This simple setup is widely used in burners to promote stabilized flames of lean mixtures.Flow patterns for sudden-expansion and diffusers are contrasted for swirl number of 1 and expansion area ratio of 4 in a transitional turbulence regime. Diffusers have important influence on size and location of recirculation zones. Hence knowledge of flow characteristics is a prerequisite in the design process. The criteria to establish the optimum diffuser would be better mixing as well as minimum residence time in the recirculation zones to prevent the formation of NOx in the future burner. The dissipated mechanical energy is not important in burner applications.Copyright