Numerical and experimental study of atrium enclosure fires in a full scale fire test facility. Póster

For the present work, a 3-D numerical model has been implemented to simulate the thermal and fluid fields induced by an enclosure fire in an atrium and for smoke exhaust system assessment. This study is focused on the ‘Fire Atrium’, a new full-scale fire test facility of the Technological Metal Centre in Murcia, Spain. It is an aluminium prismatic squared base building of 19.5 m x 19.5 m x 20 m with several vents arranged in its walls and four exhaust fans at the roof

On the feasibility of a flexible foil with passive heave to extract energy from low wind speeds

We explore numerically and theoretically the capability of flexible foils elastically mounted to translational springs and dampers at the leading edge to extract energy from low-speed winds through its passive heave motion. Given the spring and foil stiffnesses, for each damper constant the theory (which is valid for high Reynolds numbers and small foil deflection amplitudes, i.e., in absence of separation) provides analytically a minimum wind velocity for flutter instability, above which energy can be harvested, that depends on the thickness-to-chord-length ratio of the foil. Simple analytical expressions for the flutter frequency are also provided. Minimum wind speeds and corresponding flutter frequencies are characterized for a carbon fiber foil as the spring stiffness and damper constant are varied, finding that energy can be extracted from wind speeds lower than in conventional wind turbines. These theoretical predictions are assessed from full numerical simulations at Reynolds numbers corresponding to these wind velocities and for chord lengths of the order of the meter (i.e. about 106 ) using appropriate turbulence models, which allow to compute the power extracted from the wind that the flutter stability analysis cannot provid

Force and torque reactions on a pitching flexible aerofoil

Experimental measurements in a wind tunnel of the unsteady force and moment that a fluid exerts on flexible flapping aerofoils are not trivial because the forces and moments caused by the aerofoil's inertia and others structural tensions at the pivot axis have to be obtained separately and subtracted from the direct measurements with a force/torque sensor. Here we derive from the nonlinear beam equation general relations for the force and torque reactions at the leading edge of a pitching aerofoil in terms of the fluid force and moment on the aerofoil and its kinematics, involving geometric and structural parameters of the flexible aerofoil. These relations are validated by comparing high-resolution numerical simulations of the flow–structure interaction of a two-dimensional flexible aerofoil pitching about its leading edge with direct force and torque measurements in a wind tunnel.This research has been supported by the Junta de Andalucía, Spain (UMA18-FEDER-JA-047 and P18-FR-1532). Funding for open access charge: Universidad de Málaga

Influence of different make-up air configurations on the fire-induced conditions in an atrium

This paper provides with a set of full-scale experimental data of atrium fires. These data could be used as benchmarks for future numerical validation studies. In particular, the influence of the make-up air velocity as well as the position and area of the vents in an atrium is assessed both experimentally and numerically. Experimentally, the effect of different make-up air supply positions and inlet area on the fire-induced inner conditions and smoke layer descent was studied by means of three full-scale fire tests conducted in a 20 m cubic atrium. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. Later computational fluid dynamics (CFD) simulations of these tests were performed with the code Fire Dynamics Simulator (FDS). Experimentally, the lack of symmetry in make-up air vents and the large inlet area turn the flame and plume into more sensitive to outer effects. However, no significant difference has been observed between the make-up air topologies assessed. Even make-up velocities higher than 1 m/s, with symmetric venting topology, have not induced important flame or plume perturbations. Numerically, the simulations agree well with the experiments for the cases with make-up air velocities lower than 1 m/s. Poor agreement has been found for the case with inlet velocities higher than 1 m/s

Propulsion enhancement of flexible plunging foils: Comparing linear theory predictions with high-fidelity CFD results

The fluid–structure interaction of a flexible plunging hydrofoil immersed in a current is solved numerically to analyze its propulsion enhancement due to flexibility at Reynolds number 10 000. After validating with available experimental data, the code is used to assess analytical predictions from a linear theory. We consider large stiffness ratios, with high thrust enhancement by flexibility, and small mass ratios appropriate for underwater propulsion. The maximum thrust enhancement is observed at the first natural frequency, accurately predicted by the linear theory algebraically. The magnitude of the maximum thrust is over-predicted by the theory as the flapping amplitude increases. For large Strouhal numbers the flow becomes aperiodic, which for large enough amplitudes happens at frequencies below the natural frequency. But even at these Strouhal numbers, the linear theory predicts quite well the frequency of maximum thrust enhancement and optimal propulsive efficiency. We conclude that the linear theory constitutes a reliable and useful guide for the design of underwater flexible flapping-foil thrusters, and we provide a practical chart to easily select the optimal flapping frequency as a function of the actuation point, the stiffness and the mass ratios of the hydrofoil.This research has been supported by the Junta de Andalucía, Spain (Grants UMA18-FEDER-JA-047 and P18-FR-1532), and by the Ministerio de Ciencia e Innovación of Spain (Grant PID2019-104938RB-I00). Funding for open access charge: Universidad de Málaga / CBUA. The computations were performed in the Picasso Supercomputer at the University of Málaga, a node of the Spanish Supercomputing Network

Efficient self-propelled locomotion by an elastically supported rigid foil actuated by a torque

A new theoretical model is presented for an aquatic vehicle self-propelled by a rigid foil undergoing pitching oscillations generated by a torque of small amplitude applied at an arbitrary pivot axis at which the foil is elastically supported to allow for passive heaving motion. The model is based on 2D linear potential-flow theory coupled with the self-propelled dynamics of the semi-passive flapping foil elastically mounted on the vehicle hull through translational and torsional springs and dampers. It is governed by just three ordinary differential equations, whose numerical solutions are assessed with full viscous numerical simulations of the self-propelled foil. Analytical approximate solutions for the combined effect of all the relevant non-dimensional parameters on the swimming velocity and efficiency are also obtained by taking advantage of the small-amplitude of the applied torque. Thus, simple power laws for the velocity and efficiency dependencies on Lighthill number and torque intensity are obtained. It is found that the swimming velocity and transport efficiency can be greatly enhanced by selecting appropriately the non-dimensional constants of the translational and torsional springs, which are mapped for typical values of the remaining parameters in aquatic locomotion. These resonant values serve to select optimal frequencies of the forcing torque for given structural and geometric parameters. Thus, the present model and analysis provide a useful guide for the design of an efficient flapping-foil underwater vehicle.This research has been supported by the Junta de Andalucía, Spain, through the project grants UMA18-FEDER-JA-047 and P18-FR-1532. The computations were performed in the Picasso Supercomputer at the University of Málaga, a node of the Spanish Supercomputing Network. // Funding for open access charge: Universidad de Málaga / CBU

Low and medium power full-scale atrium fire tests and numerical validation of FDS

The inclusion of atria within modern large buildings is relative recent. These structures are important architectonical features since the 60’s. Atria are a source of discussion within the fire science community. They introduce complex designs and non conventional architectonical elements that can lead to fire environments diverging from those in current codes. Because of this, the current trend in fire safety in atria is towards performance based design. At this point, it is still necessary to improve and validate the existing numerical models. For this aim, some tests were carried out at the Murcia Fire Facility. These consist of 19 full-scale fire tests that provide with new experimental data of atrium fires. The fire size, the smoke extraction rate and make-up openings size and location were varied. At the present paper, a set of results from some of these experiments in a 20 m cubic facility are reported and discussed. Additionally, comparisons with the predicted results from Fire Dynamics Simulator (FDS) v.4 are also presented. FDS has turned out to be capable to predict the transient fire-induced conditions inside the facility accurately, above all at the upper parts. The predicted smoke layer descent has been also compared with the experimental one with good agreement.The authors want to acknowledge the Centro Tecnológico del Metal of Murcia for the use of their test rig, the Professor J. L. Torero, T. Steinhaus, C.Abecassis-Empis, P. Reszka, W. Jahn, from the University of Edinburgh, for their technical suggestions and supervision. Simulations have been carried out at the computational facilities of the Technological Research Services of the Technical University of Cartagena (SAIT) and the University of Jaen. This work has been supported by Ministerio de Educación y Ciencia of Spain (Projects CT/G30572473, and FIT-020700-2004-25 and grant TRA2006-15015) and by the Junta de Andalucía of Spain (Project number P07-TEP-02693)

Método y sistema de evaluación de transformaciones morfológicas de una cavidad nasal

Número de publicación: 2 732 713 Número de solicitud: 201830500Método y sistema de evaluación de transformaciones morfológicas de una cavidad nasal que comprende, para cada transformación morfológica (ax) bajo análisis, simular (550) un flujo (F) en un modelo tridimensional modificado (Mx 3D) por dicha transformación morfológica (ax) y analizar al menos un primer parámetro (ϕ) y un segundo parámetro (R) calculados (560) a partir de dicho flujo (F) y dicho modelo tridimensional modificado (Mx 3D). El primer parámetro (ϕ) es una medida de asimetría morfológica y fluido-dinámica, mientras que el segundo parámetro (R) es una medida de resistencia bilateral de la combinación del pasaje nasal izquierdo y del pasaje nasal derecho. El primer parámetro (ϕ) y el segundo parámetro (R) se comparan (570) con unas condiciones de validación (570), obteniendo así una evaluación (ev) de cada transformación morfológica (ax) bajo análisis.Universidad Politécnica de Cartagen

On the Fluid Dynamics of the Make-Up Inlet Air and the Prediction of Anomalous Fire Dynamics in a Large-Scale Facility

The present paper is focused on the fluid dynamics of the make-up air at the vents in case of an atrium fire, its influence on the fire-induced conditions and the necessity of properly model it to obtain an accurate numerical prediction. For this aim, experimental data from two full-scale atrium fire tests conducted in a 20 m cubic facility, with venting conditions involving mechanical smoke exhaust and make-up air velocities larger than 1 m/s, and with different fire powers, are presented. Subsequent numerical simulations of these tests have been performed with the code Fire Dynamics Simulator v5.5.3. Two different approaches have been followed to simulate the make-up air inlet fluid dynamics, involving one domain which only considers the inside of the building and another which includes part of the outside. In the former simulations, anomalous phenomena around the fire appear, while the inclusion of the exterior domain provides with a completely different fluid dynamics inside the facility which agrees better with the experimental data. A detailed analysis of the fluid mechanics at the air inlet vents is conducted to explain these discrepancies. Finally, further simulations are performed varying the make-up area to assess the appearance of the aforementioned phenomenon.This research was supported by the Spanish MCyT and Junta de Andalucia under Projects # DPI2008-06624-C03-02 and # P07-TEP02693, respectively. CGM wants to acknowledge the research stay grants IAC-2010-3 and A-13-2010 from the Junta de Andalucia and the University of Jaén, respectivel

Experimental Data and Numerical Modelling of 1.3 and 2.3 MW Fires in a 20 m Cubic Atrium

Research paper published in the peer-reviewed journal Building and Environment.Atria and large spaces are common architectonical features in modern buildings such as high rises, auditoria, warehouses, airports and mass transport stations among others. There is currently an international trend towards the performance-based design for fire safety of these building elements. This design process relies heavily on fire modelling but the knowledge in fire dynamics and the movement of smoke in atria and large spaces still presents some gaps. This paper aims at contributing to close these gaps and reports the three Murcia Atrium Fire Tests conducted in a 20 m cubic enclosure using pools of 1.3 and 2.3 MW. Detailed transient measurements of gas and wall temperatures, as well as pressure drop through the exhaust fans and airflow at the inlets were recorded. The study also includes the effect of the mechanical exhaust ventilation. Results have been compared with those predicted by the computational fluid dynamics (CFD) model Fire Dynamics Simulator FDSv4. In general terms, the comparisons between experiments and simulations show good agreement, especially in the far field of the plume, but the accuracy is poor at the lower plume region and near the flame