In this work, a numerical 3D simulation of a longitudinal ventilation system (LVS) is developed to analyze the fire behaviour inside a road tunnel. The numerical modelling reproduces the Memorial Tunnel, a two-lane, 853 m long road tunnel, used for experimental purposes. On this tunnel, 98 full-scale fire ventilation tests with different ventilation systems were conducted, constituting the first significant experimental approach to analyze fire incidents inside road tunnels. A total number of 24 reversible jets fans were installed in groups of three, nearly equally spaced over the length of the tunnel, and cantilevered from the ceiling of the tunnel. The validation of a numerical model is developed in the present paper. For that purpose, the behaviour of the smoke generated during a fire incident inside a road tunnel is predicted and compared with previous experimental data collected in the Memorial Tunnel Project. The smoke evolution and the performance of the LVS is simulated with a commercial code, FLUENT, which allows 3D unsteady simulations of the Navier-Stokes equations for multispecies mixtures of gases. A sufficient mesh density was introduced for the spatial discretization in order to obtain accurate results in a reasonable CPU time. Hence, typical ratios between total number of cells and the overall tunnel length were employed in the modelling. As a result, good agreement was achieved in all the tested cases, defining an accurate methodology to predict the performance of a LVS in case of fire inside a tunnel.

During the last decades, the Asturian Central Coal Basin (ACCB) has been a highly exploited coal mining area by means of underground mining and its network of tunnels extend among more than 30 mines. Parts of this infrastructure will soon become available for alternative uses since most of the coal mining facilities in Spain will fade out in 2018. Increasing penetration of renewable energy sources into the electrical grid, with intermittent and fluctuating supply, leads to excessive frequency variations, so the development of energy storage technologies are required, such as Pumped Storage Hydroelectricity (PSH). Reduced environmental impacts, deep, non-flooded shafts and abundance of water from underground runoff , make coal mines in ACCB suitable for the development of Underground Pumped-Storage Hydropower projects (UPSH). The network of tunnels of a mine facility has an unusual geometry for a water storage system. Although there are numerous studies for the construction of UPSH plants, until now there have been no known projects of this type under operation. Filling and emptying processes during the operation of the turbine-pump are complex due to the presence of two fluids interacting inside the tunnels, water and air. This paper explores the viability of a network of tunnels as an underground water reservoir. Two-phase three-dimensional CFD models have been developed in order to know the flow behavior in the tunnels. The pressure and velocity results that have been obtained in the simulations confirm that the use of underground mines as a lower reservoir of a UPSH is technically possible.

This paper analyzes the structure of turbulence in a single stage, low-speed axial fan with inlet guide vanes. Turbulence intensity values and integral length scales have been obtained using hot-wire anemometry for three different operating points and two different axial gaps between the stator and the rotor. These measurements were carried out in two transversal sectors, one between the rows and the other rotor downstream, covering the whole span of the stage for a complete stator pitch. Since total unsteadiness is composed of the contribution of both periodic and random unsteadiness, a processing data method was developed to filter deterministic unsteadiness in the raw velocity traces. Velocity signals were transformed into the frequency domain by removing all the contributions coming from the rotational frequency, the blade passing frequency and its harmonics. Consequently, coherent flow structures were decoupled and thus background levels of turbulence-RMS values of random fluctuations-were determined across the stage. Additionally, this unsteady segregation revealed further information about the transport of the turbulent structures in the unsteady, deterministic flow patterns. Therefore, anisotropic turbulence, generated at the shear layers of the wakes, could be identified as the major mechanism of turbulence generation, rather than free-stream, nearly isotropic turbulence of wake-unaffected regions. Finally, spectra and autocorrelation analysis of random fluctuations were also used to estimate integral length scales-larger eddy sizes-of turbulence, providing insight on the complete picture of the turbulent flow.

In 2017, renewable energy accounted for 19.5% of the total energy used for heating and cooling in the European Union. This paper analyses the technical and economic feasibility of using mine water from flooded underground coal mines in Spain to provide renewable thermal energy to buildings located in surrounding areas. High efficiency heat pump system is proposed to provide sustainable energy for district heating and cooling, leading to a reduction of greenhouse gas emissions to the atmosphere. The results obtained show that 20 MW of thermal energy is available for heat recovery from mine waters, compared to 4 MW of electrical power committed for pumping from inside the mines and heat pump consumption. The economic model that has been developed indicates that the feasibility of the geothermal plants depends on the amount of thermal energy demanded, the efficiency of the system and the distance from the abandoned mines to potential users. A mine water geothermal plant with 10 MW of power provides energy for about 1,700 households at a distance of 2 km with an investment cost of 3.25 MV. Regarding the reduction of CO 2 emissions, the emission factor is reduced to 0.048 kgCO 2 kWh À1 using this approach.

The present study is focused on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single stage, low-speed axial fan with inlet guide vanes. The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow fan of high reaction degree, relating them to working point variations and axial gap modifications. For that purpose, an experimental open-loop facility has been developed to obtain a physical description of the flow across the turbomachine. Using hot-wire anemometry, measurements of axial and tangential velocities were carried out in two transversal sectors: one between the rows and the other downstream of the rotor, covering the whole span of the stage for a complete stator pitch. Ensemble- and time-averaging techniques were introduced to extract deterministic fluctuations from raw data, both of which are essential to understand flow mechanisms related to the blade passing frequency. An exhaustive analysis of the measured wakes has provided a comprehensive description of the underlying mechanisms in both wake-transport phenomena and stator-rotor interaction. In addition, unmixed stator wakes, observed at the rotor exit, have been treated in terms of dispersion and angular displacement to indicate the influence of the blades loading on the transport of the stator wake fluid. The final aim of the paper is to highlight a complete picture of the unsteady flow patterns inside industrial axial fans.