Lateral channeling within rectangular arrays of cubical obstacles

Water channel experiments were conducted with the goal of obtaining better understanding of flows through urban-like arrays of buildings. Particle Image Velocimetry (PIV) was used for comprehensive flow measurements within a modeled simple urban setup. Building arrays were modeled using acrylic blocks whose refractive index is the same as that of salty water. Such a setup allowed for undisturbed laser sheet illumination through the obstacles enabling detailed flow measurements between the obstacles/buildings. Building array size, measurement plane and flow conditions were varied. A novel flow feature, lateral channeling, observed and quantitatively measured, within regular 3×3 and 5×5 arrays of cubes is reported here. A sideways mean outflow from the building array is observed behind the first row of buildings followed by the mean inflow in the lee of all succeeding rows of buildings. When the central building in a 3×3 array is replaced by a building of double height, due to the strong downdraft caused by this tall building, the lateral outflow becomes significantly more intense. When the central building in a 5×5 array is replaced by a building of double height, the building downdraft blocks the lateral inflow to the array. This is the first time that such detailed measurements are available for a mock urban array of finite size—a real three-dimensional case. The newly identified mean flow pattern may be accountable for the initial plume spread within an array of obstacles.     

Numerical and experimental investigation of a gully under surcharge conditions

This paper deals with numerical and experimental investigation of a gully under exceptional situations after the sewer system becomes pressurized. These results are useful for the calibration and validation of the linking elements found in Dual Drainage (DD) models. The experimental results were obtained in the MLE (Multiple-Linking-Element) experimental installation that allows the simulation of full surcharge flow through a gully. The installation consists of an 8 m long and 0.5 m wide channel, fitted with a 0.6 × 0.3 × 0.3 m gully with a 80 mm diameter pipe inlet at the bottom. The numerical results were obtained using a three-dimensional structured mesh simulated in the OpenFOAM^TM Toolbox. The results characterization focuses mainly on the jet area, whereby pressure-flow relations were derived for this specific gully. The good agreement found between numerical and experimental results, allowed the extrapolation to larger flow rates.     

The Use of Positive Pressure Ventilation Fans During Firefighting Operations in Underground Stations: An Experimental Study

Positive pressure ventilation (PPV) fans are widely used by the fire service during firefighting operations in buildings. Fans are positioned to create a flow through the enclosure. This flow can remove the smoke after the fire or affect the direction of the smoke to support firefighting operations. In subway stations, it is less common to use PPV fans. Here, 106 full-scale tests with up to four fans have been performed in a training building that represents a subway station. The fans were used as extraction fans. The generated flow through the subway station has been measured. The critical velocity for a hypothetical tunnel (W × H: 3.17 × 4.15 m) attached to the subway station has been calculated as 2.37 m/s. Reaching the critical velocity has been used as criterion for ‘success’. All combinations with four fans exceed this velocity, supporting the idea that the fans could be used to facilitate a firefighting operation. The location of the fans was varied. Combinations with three fans on the platform and one at the top of the staircase performed better than combinations with two fans on the platform, one on the landing and one at the top of the staircase. There is an optimum value for the distance between the fans on the platform and the first step of the staircase. This value depends on the angle of inclination of the fans. The fans were not capable of creating a flow that exceeded the critical velocity in the station itself (L × W × H: 60 × 7.15 × 4.53 m). However, a velocity of 2.40 m/s corresponds to a flow rate that will limit the backlayering distance in the station to 15 m. This was only achieved by tests with four fans (three on the platform and one at the top of the staircase).     

Structure and Evaluation of the Process for Origin Determination in Compartment Fires

The science behind the formation of fire patterns and their ensuing use in the forensic analysis of fire scenes has been questioned since their introduction in the 1940s. This paper provides an overview of a prototype method for determining the area of origin based on fire patterns analysis, named the process for origin determination (POD). The POD is a seven step reasoning process for evaluating fire damage, which starts by identifying the value in further analysis of each surface and compartment of a structure and then procedurally evaluates each surface for use within the overall determination. This paper outlines the application of the POD with test subjects and presents an analysis of the outcomes showing its benefits. To facilitate testing the POD, numerical simulations and physical experiments were employed. The numerical simulations were completed through the use of fire dynamics simulator simulating a single compartment measuring 3.66 m × 3.66 m × 2.44 m with a single ventilation opening. The physical experiments were tests conducted specifically for fire patterns where accuracy rates had been previously identified in the literature. Sixty test subjects participated in the evaluation of thirty-two different origin scenarios. A decrease in variability, which indicates an increase in reliability, was noted in 21 of the 32 scenarios (66%) when participants used the POD. Three accuracy measurements were employed, all three of which illustrated an increase in accuracy when participants used the POD. The accuracy was shown to increase between 50% and 94% when participants used the POD.     

Spray Measurements of an Upright Fire Sprinkler

Measurements were conducted to characterize the spray patterns of an upright fire sprinkler in the near and far field of the sprinkler. The spatial distribution of droplet size, velocity and number density in the spray was measured using a laser-based shadow-imaging system. The water volume flux distribution was measured by an array of pressure-transducer-equipped water collection tubes and containers. A large-scale traverse was constructed to move the laser optics and water collection tubes and containers to the designated measurement locations. An upright fire sprinkler with a K-factor of 162 lpm/bar^1/2, installed with its deflector 0.17 m below a flat horizontal ceiling, was characterized at two discharge pressures, i.e., 0.76 bar and 1.31 bar. In the near field at 0.76 m from the sprinkler, measurements were performed in a spherical coordinate at different azimuthal and elevation angles with respect to the sprinkler deflector. In the far field, the sprays were mapped out in a 110° circular sector at 3.05 m and 4.57 m below the ceiling. The shadow-imaging based water flux measurements were verified by the measurements obtained from water collection containers. Except for the pipe effect, the azimuthal distributions of the flow rate showed that the spray pattern was more influenced by the frame arms than by the deflector tines and slots. The gross droplet size distribution was expressed as a combination of a log-normal function and Rosin–Rammler function. The median droplet diameter was correlated as an empirical function of the sprinkler orifice diameter and operating pressure. The near-field distributions of the droplet size, velocity and flux can be used to prescribe the starting spray conditions for numerical simulations of spray transport. The far-field measurements are useful in evaluating the spray transport calculations.     

Smoke Movement in a Sloping Subway Tunnel Under Longitudinal Ventilation with Blockage

Critical velocity and smoke back-layering length are two of the determining parameters to the fire risk assessment of subway tunnel. These two parameters of a sloping subway tunnel with train blockage were investigated both experimentally and numerically in this paper. To address the influences of slope, the slopes of 0, 3, 6, 9, 12, 15% in downhill subway tunnel were studied and the height (H) of the tunnel was replaced by the inclined tunnel height (\( H/\cos \theta \)). The train model with a dimension of 2 m (length) × 0.3 m (width) × 0.38 m (height) was also chosen in simulations and experiments for the tunnel blockage. Thenceforward, 30 reduced-scale experimental and 150 numerical scenarios were analyzed to predict the critical velocity and smoke back-layering length in various sloping subway tunnels. Six different heat release rates including 5.58, 11.17, 16.67, 22.35, 27.94, and 33.52 kW were considered in the experiments and five different heat release rates including 2.79, 5.58, 8.38, 11.17 and 16.67 kW were considered in the simulations. Based on the comparison in the horizontal tunnel, numerical results were quite consistent with the experiments. The results showed that train blockage influenced the smoke back-layering length, and the critical velocity increases with the tunnel slope. Finally, empirical models were developed to predict the critical velocity and smoke back-layering length in a sloping subway tunnel with train blockage.     

Experimental study of cooling water pipe circuits by theoretical and numerical analysis in a reactor vault

Our aim is to study the heat transfer processes in a cooling circuit. In this project, a mild steel plate of 1.1 m?×?1.1 m?×?6 mm dimensions is used. Square pipes are embedded in a liner plate, through which the water is circulated to remove heat from the reactor vault. To improve the contact between the pipes and the liner, the pipes are welded to the liner throughout their length. A heater plate simulating main vessel was placed, and the electrical heaters were laid all over the inner surface of main vessel. The square pipes were made to let the water flow through them, and the flow rate is set using a flow meter and this water is heated by convection and it is condensed by passing through a heat exchanger. Thermocouples are fixed at different locations of cooling pipes, the liner and the water inlet/outlet.     

Numerical Studies on Thermally-Induced Air Flow in Sloping Tunnels with Experimental Scale Modelling Justifications

Study of smoke movement or air flow due to fire in sloping tunnels is important in designing smoke control systems. In contrast to a horizontal tunnel, there is an acceleration along the longitudinal axis due to smoke buoyancy. This phenomenon together with thermal radiation would lead to a complicated heat transfer mechanism of the ceiling jet in sloping tunnels. In the present work, thermally induced air flow arising from fire in sloping tunnels was studied via numerical simulations using the Computational Fluid Dynamics code FLUENT. Prior to the application of FLUENT in simulating the air flow under different conditions, scale model experiments were carried out and the results were compared with simulation results, to establish the reliability of FLUENT in simulating fires in sloping tunnels. For this purpose, a tunnel section model of length 3 m, width 0.8 m and height 1 m was constructed, with a 1.5 kW electrical heating source to model fire. Hot air movement pattern driven by the electric heater was studied with the tunnel inclined at 0°, 10°, 20° and 30° to the horizontal. Four cases of the same configuration as the scale tunnel experiments were simulated using FLUENT, with predicted results agreeing well with experimental results. Having established the suitability of FLUENT in simulating air flow due to fire in sloping tunnels, numerical simulations were carried out to study air flow in sloping tunnels with different scenarios, that is, for tunnels with different gradients and with fire located at different positions in the tunnel. Macroscopic number on heat transfer, including the Rayleigh number Ra, the average and local Nusselt number Nu_ave for sloping tunnels were also studied from the measured results. The correlation between Nu_ave and Ra, which shows the effect of hydrodynamic properties on relative dominance of heat transfer in tunnel fire, was also discussed.     

Air entrainment and turbulent fluctuations in hydraulic jumps

A hydraulic jump is the sudden transition from a high-velocity impinging flow into a turbulent roller in an open channel. Substantial amounts of air are entrapped at the impingement point, and significant free-surface fluctuations take place above the roller. In the present study, some physical modelling was conducted in a relatively large sized facility. The flow conditions included a wide ranges of inflow Froude numbers and Reynolds numbers (3.8 < Fr₁ < 10.0, 2.1 × 10⁴ < Re < 1.6 × 10⁵). The fluctuating features of free-surface and roller position were investigated non-intrusively with a series of acoustic displacement meters. The characteristic frequencies of the fluctuating motions were documented, and some major roller surface deformation patterns were revealed. The air-water flow properties were investigated with an intrusive phase-detection probe. The void fraction and bubble count rate data were documented in the jump roller, together with the interfacial velocity distributions. The rate of air entrainment was estimated based upon the void fraction and interfacial velocity distribution data. Some simultaneous measurements of instantaneous void fraction and free-surface fluctuations as well as longitudinal jump front oscillations were conducted. The relationship between the rate of air entrainment and turbulent fluctuations is discussed. Both the turbulent fluctuation and aeration properties are basic design parameters in urban water systems in which a hydraulic jump may take place. The present work provides relevant information for water systems including covered channels and partially-filled pipes.     

Computational modelling of large aerated lagoon hydraulics

A good understanding of the hydraulic performance of aerated lagoons is required for their design and operation. A comprehensive numerical procedure has been developed for the three-dimensional computational modelling of the flow in large lagoons including high-speed floating mechanical surface aerators. This paper describes the procedure that consists of separate aerator modelling, then applying the obtained results as boundary data for a full lagoon model. A model application to an industrial aerated lagoon serves as an example of flow analysis. Post processing of the results by calculating the local average residence time (age of fluid) provides a powerful and intuitive technique to visualize and analyse the lagoon performance. The model has been verified by comparing the local average residence time predictions with measurements from a dye study. It is shown that the numerical modelling proposed is feasible and constitutes an effective new tool in improving the performance and design of industrial lagoons.     

Experimental and Numerical Study of Window Glass Breakage with Varying Shaded Widths under Thermal Loading

To investigate the effect of shaded width on the breaking behavior of window glass, a series of experiments was carried out on float glass with dimension of 600 mm × 600 mm × 6 mm in an enclosed compartment under radiant heat. The shaded width of glass pane ranged from 10 mm to 50 mm with an interval of 10 mm. Experimental results showed that crack patterns of the glass pane were influenced little by the shaded width, while the average value of the first breaking time of the glass pane decreased firstly and then increased with an increase in the shaded width. The average time to the first crack with the shaded width of 20 mm was shortest in experiments and the corresponding time was 572.5 s. In addition, the finite element method was also used to simulate the process of crack initiation and single crack propagation. Temperatures measured by thermocouples in experiments were employed as thermal loads for the problem of glass breakage. The first breaking time obtained by the program was in good agreement with experimental data.     

The Breakage of Float Glass with Four-Edge Shading Under the Combined Effect of Wind Loading and Thermal Loading

The glass breakage in high-rise building fires may be significantly influenced by both the compartment fire and the environmental wind. In this work, float glass panes supported by the frame with a dimension of 600 × 600 × 6 mm³ were employed to study the glass breakage under the combination of wind and fire effects. The first breaking time, glass temperature, crack patterns, and fallout were obtained. With an increase of wind speed, the average value of temperature difference between the mean temperature at the heated exposed side and that at the ambient shaded side decreased gradually when crack initiated. The average time to first crack was maximum without wind loading and decreased gradually as the wind speed increased. Comparing with the glass breakage only under thermal radiation, the combination of environmental wind accelerated the glass breaking. The present results suggest that the wind effect should be considered for building fire protection in the window glass design.     

Flexural behaviour of reinforced concrete beams under freeze–thaw cycles and sustained load

This paper presents an experimental investigation on the flexural behaviour of reinforced concrete beams under the combined effects of freeze–thaw cycling and sustained loading. Thirteen beams (2000 × 250 × 150 mm) were fabricated and tested. Test parameters included four numbers of freeze–thaw cycles (20, 40, 60 and 80) and three levels of sustained load (0, 20 and 50% of the ultimate load of the control beam). After exposure, the beams were tested at room temperature under four point bending up to failure. The flexural behaviour was evaluated by studying the load-deflection curve, the ultimate load capacity, the ductility, the crack pattern and crack width and the evolution of the neutral axis depth. It was found that freeze–thaw cycles and sustained loading had significant effects on the flexural performance of reinforced concrete beams.     

Hydraulische Leitfähigkeiten von Sedimentwürfeln vor und nach einem gefrorenen Zustand

To study flow and transport processes in heterogeneous porous media, frozen sediment cubes that were assembled in sandbox experiments may represent a viable procedure. In this investigation, it was important to find out how flow and transport properties would be modified by sediment freezing. In this study, a medium sand, a coarse sand and a fine gravel were investigated to find out to what extent the hydraulic conductivities might change before and after freezing. For this purpose, a cubic Darcy-cell was developed. The results of the study show that it is possible to produce 10?×?10?×?10 cm frozen sediment cubes with the presented apparatus. The study also suggests that freezing and subsequent thawing only caused small changes in hydraulic conductivity of the investigated sediments.     

Prediction of the pressure distribution on a cubical building with implicit LES

This paper presents a numerical study of the flow around a cubical building in an atmospheric boundary layer. The Reynolds number of the flow is Re=4×10⁶. Different types of turbulence models, steady state RANS, hybrid RANS/LES and LES, are used and the simulation results are compared to field measurement data of the mean pressure distribution. The objective is to build an approach to perform simulations on coarse grids with low computational cost. The outcome is that the Implicit LES (ILES) method is the most accurate for coarse grid simulations. In order to verify the sensitivity of the results to the Reynolds number, also simulations of a wind tunnel experiment at Reynolds number 4×10⁴ are performed. We demonstrate that also for lower Reynolds numbers, although not optimal, the ILES approach leads to quite good results.     

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on façades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m³ lower compartment of a two levels high concrete structure. External flames develop in front of the façade from the fire compartment through windows with dimensions 1?×?1.5 m (W?×?H). In order to predict the fire exposure of a façade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested façade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the façade during calibration tests and can be used for further evaluation of combustible material on façade.     

Numerical modeling for the coupled thermo-mechanical processes and spalling phenomena in spPillar Stability Experiment (APSE)

In this paper, the coupled thermo-mechanical (TM) processes in the sp Pillar Stability Experiment (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both continuum and discontinuum based numerical methods. Two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) and 2D distinct element method (DEM) with particles were used. The main objective for the large scale in situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing of one of the boreholes and heating. For the DEM simulations, the heat flow algorithm was newly introduced into the original code. The calculated stress, displacement and temperature distributions were compared with the ones obtained from in situ measurements and FEM simulations. A parametric study for initial microcracks was also performed to reproduce the spalling phenomena observed in the APSE.     

Geohydrological properties of selected badland sediments in Saskatchewan,Canada

Geological and seasonal weather variations govern the geohydrological properties of the Avonlea badlands in Saskatchewan, Canada. Three surface sediments exhibiting distinct lithologic variations were found: a steeply sloped and fissured sandstone; a mildly sloped and popcorn-textured mudrock; and a flat and eroded pediment. The fines content increased from the dry to the wet state, with contents of 17–33 % seen for sandstone, 4–98 % for mudrock, and 21–42 % for pediment. The water adsorption capacity was found to be highest for mudrock (w _l = 96 % and w _p = 47 %), followed by sandstone (w _l = 39 % and w _p = 31 %), and then by pediment (w _l = 31 % and w _p = 23 %). The soil water characteristic curves of sandstone and mudrock showed bimodal distributions with a low air entry value (6 and 9 kPa) pertaining to drainage through cracks and a high air entry value (160 and 92 kPa) associated with flow through the soil matrix. The pediment presented a unimodal soil water characteristic curve with a single matrix air entry value of 4 kPa. The saturated hydraulic conductivities for sandstone, mudrock, and pediment were measured as 8.5 × 10^?6, 4.0 × 10^?8, and 1.8 × 10^?5 m/s, respectively.     

The Effect of Boundary Layer on Blow-Off Extinction in Opposed-Flow Flame Spread over Thin Cellulose: Experiments and a Simplified Analysis

Study of flame spread plays a crucial role in our understanding of fires with direct implications to fire safety. Flame-spread in an opposing flow configuration and relative blow-off extinction in the kinetic regime have been studied for the last few decades. It is known that the extinction velocity is related to the Damköhler number, the ratio of residence time to the combustion time at the flame leading edge. It is also well known that the behavior of the flame is affected by the presence of the boundary layer. However, there is no experimental evidence in literature to quantify the boundary layer effect. In this work we experimentally establish the effect of boundary layer development length on the extinction velocity, opposed flow velocity of the oxidizer at which the blow-off extinction occurs, for flame spread over thin fuels. Using a vertical combustion tunnel, a large number of downward flame spread experiments over thin ashless filter paper are conducted for an opposed flow velocity range of 40 cm/s to 100 cm/s. The extinction length, the distance from the sample leading edge at which the blow-off extinction occurs, is shown to be directly related to the opposing flow velocity. A correlation between the two based on scaling analysis and on an empirical law reveals that blow-off extinction occurs at a constant effective velocity. This simple conclusion can have implications in future refinement of Damköhler number correlations for blow-off extinction.     

3-Dimensional numerical modeling of geosynthetic-encased granular columns

In this paper, series of three-dimensional (3-d) numerical modeling of geosynthetic-encased granular columns were performed both in model and prototype scale using FLAC^3D software to understand the lateral load carrying capacity of ordinary and geosynthetic encased granular columns (OGC and EGC). In the first part of the study, numerical modeling of direct shear tests were carried out. The soil in the direct shear box was reinforced with two different diameters of granular columns (50 mm and 100 mm) and three different patterns of arrangement (single, triangular and square) to study the effect of group confinement. The numerical simulations were carried out at four different confining pressures namely 15, 30, 45 and 75 kPa. From the numerical simulations it was observed that higher shear stresses are mobilized inside the granular column due to geosynthetic encasement and the magnitude of shear stress increases with increase in the normal pressure. It was found that the tensile forces in the geosynthetic encasement were mobilized both in circumferential and vertical directions, which helps in mobilizing additional confinement in the granular column. In the second part, the influence of the geosynthetic encasement of granular column treated soft ground was demonstrated through 3-dimensional slope stability analyses.