Smoke Flow Research Articles

Study on the Influence of Ventilation Speed on Smoke and Temperature Characteristics of Complex Underground Spaces

This study explores the intricate behaviors of smoke flow, temperature distribution, carbon monoxide (CO) levels, and visibility dynamics within complex underground spaces during fire incidents. A key revelation is the profound impact of ventilation speed, with the identification of a critical range between 2 and 3 m/s that consistently proves to be instrumental in curbing smoke-related hazards and ensuring the safe evacuation of personnel. Furthermore, this paper underscores the influence of accelerated longitudinal winds on temperature profiles, particularly under high HRR conditions, underscoring the importance of accounting for wind effects in comprehensive fire response strategies. Regarding CO concentration, which is a critical safety concern, this study demonstrates that higher ventilation speeds effectively reduce hazardous gas levels, thereby fortifying overall safety measures. The visibility is analyzed, with the findings indicating that elevated ventilation speeds enhance visibility, albeit with considerations about potential drawbacks on personnel evacuation due to excessive wind speed. In conclusion, this paper offers a comprehensive understanding of the pivotal role played by ventilation speed in underground space safety by encompassing smoke control and temperature management.

Study on the influence of the longitudinal position of fire source and tunnel width on the maximum ceiling gas temperature

Tunnel fires can result in significant damage to both personnel and property due to the high temperature generated. In this research, a set of numerical simulations were carried out to investigate the smoke flow characteristics in a tunnel with a variable placement of the fire source along the longitudinal centerline. The results showed that due to the influence of the width and the location of the fire source, when the fire source is closer to the upstream portal, most of the air supplied for combustion will come from the upstream, and the downstream cold air will be subjected to more intense smoke entrainment, resulting in different supplementary wind speeds on both sides and an inclined flame. Meanwhile, as the fire source moves from the upstream opening towards the center of the tunnel, the flame changes from inclined to vertical, and the air supplied for combustion shifts mostly from the upstream portal to evenly from both sides. The maximum ceiling gas temperature gradually increases to a maximum value in a non-linear pattern. The empirical equations were suggested for estimating the maximum ceiling gas temperature at various longitudinal positions within the tunnel.

Water spray effects on fire smoke temperature distribution beneath a symmetrical V-shaped tunnel ceiling

The coupling effects of the double-slope stack effect, the thermal buoyancy induced by the V-shaped tunnel fire and the drag force generated by the water spray system alter fire smoke flow regulation compared to fire smoke flow in a horizontal tunnel. By numerical simulation, this work investigates the effect of water spray flow rate (0 L/min – 600 L/min), atomization angle (0–150°) and the length within fire source and the grade change point (0–120 m) on smoke temperature distribution beneath a symmetrical V-shaped ceiling. The findings indicate that the cooling effect on smoke temperature can be significantly improved by increasing the rate of water spray flow, while water spray increasing angle and tunnel slope have little contribution to the cooling smoke temperature. Thus an improved ceiling smoke temperature distribution model is proposed by importing the flow rate, angle coefficients and tunnel slope. As the fire source distance from the grade change point increases, stack effect on fire smoke flow could be categorized into three zones, which are the double-slope control zone, the transition zone and the single-slope control zone, which causes that downstream smoke temperature become higher gradually than the upstream one, while the smoke temperature difference tends to stabilize at the single-slope control stage. Finally, a global ceiling smoke temperature distribution in the symmetrical V-shaped tunnel installed a water spray system is established by introducing fire source distance coefficients.

Fire control and self-extinguishment by blocking smoke flow with water spray in a tunnel fire

This study clarified the effect of water spray on fire control and extinguishment in a tunnel fire. A series of fire experiments were conducted using a 1:10 scale model tunnel to investigate the performance of water spray for suppressing the fire and blocking the smoke produced by the fire. The water spray trapped the smoke in the fire zone and prevented the inflow of fresh air from the tunnel portal. That is, the water spray sealed off the smoke and compartmentalized it in the tunnel. A calorimetry method was developed to estimate the chemical heat release rate (HRR) in the tunnel with the sealed-off descended smoke. Within the test conditions considered in this study, the following results were obtained. First, self-extinguishment occurred in 86% of the cases tested in the fire zone sealed off by the water spray. Second, the maximum HRR of the vitiated fire induced by the water spray was reduced to one-fifth compared to that during free burning. Finally, a ghosting flame and self-extinguishment by suffocation occurred when the smoke blocking rate exceeded about 60% and 80%, respectively.

Study on smoke flow characteristics in immersed tunnel fires with lateral centralized exhaust: Considering the effect of the slope

In the case of fires in inclined immersed tunnels, smoke flow patterns differ from those of horizontal tunnels, and require a unique approach to lateral centralized smoke exhaust. In this study, we propose a prediction model for the exhausted mass flow rate near each vent and use Fire Dynamics Simulator (FDS) to analyze the flow field and components. Our findings indicate that temperature and smoke velocity distributions follow exponential decay with varying slopes, with exhaust efficiency and entrainment coefficient first increasing then decreasing at 1% and 2% slopes, and continuously decreasing at 3%, 4%, and 5% slopes. Only at a 6% slope can the smoke reach the nearest vent. Exhausted mass flow rate and exhaust volume have a positive correlation, and calculated values and simulated results agree well. This study can guide the design and management of lateral centralized smoke exhaust systems for inclined tunnels.

Experimental study of dynamics of flames from discrete methanol fuel wicks in ullages

The paper presents an experimental study of the burning characteristics of discrete methanol wicks in ullages, where the burning occurs at distances much lower than the lip of the burner. Burning configurations consisting of two methanol wicks burning in varying ullages (from zero to 24 cm at intervals of 6 cm) have been considered in the experiments. At zero and 6 cm ullages, flame shapes resemble that of a general buoyant pool flame. As the ullage is increased to 12 cm or higher, a plume-induced instability triggers in the ullage and the flame bends towards one side over the wicks, resembling a boundary layer type of flame. The transition from a pool flame to a boundary layer-type flame has been illustrated with direct flame photographs. At deeper ullages, as the flame leans over the fuel wicks, the mass burning rates are enhanced from 9% to 35% for different ullages. The resulting air flow inside the ullage and flame shape affects the mass burning rate and has been visualized using smoke flow in the ullage. This study opens further research on the coupling effect of burning of heterogeneous materials in ullages with the flow field induced by the buoyant plume.

An experimental study on the smoke spread in underground interconnected infrastructure with longitudinal ventilation

The underground interconnected infrastructures are under development in the metropolitan areas, and simultaneously, also raise many safety issues, especially with regards to the smoke control once a fire occurred. Owing to the interconnected structure, the smoke spread in underground interconnected infrastructures can be more complex than that in “normal” tunnels, where the smoke spread is commonly simplified as one-dimensional spreading. In this study, the properties of maximum temperature, temperature decay, and smoke spread in a longitudinally ventilated underground interconnected infrastructure were studied. Experiments were conducted in a reduced-scale model which was divided into the tunnel part A and part B, and the scenario of a fire occurring at the junction point was mainly considered. For such a scenario, it is found that the temperature decay depends on the ventilated velocities of both upstream and connected tunnel sections. The spreading of the smoke in the upstream tunnel section depends on the ventilated velocity of the upstream tunnel section and can be well described by previous back-layering correlation. Whereas for the spreading of smoke in the connected tunnel section, both the ventilated velocities in the upstream and connected tunnel sections show a distinct impact. The estimation of whether the smoke spreads to the connected tunnel is established by comparing the buoyance force of the smoke and the inertia force of the ventilated flow. It is indicated that the smoke flow will be less inclined to spread to the connected tunnel under the scenarios of weak buoyancy force and large ventilated velocity. The findings of this work may contribute to an improved understanding of thermal-driven smoke propagation in underground interconnected infrastructures.

Effect of crossflow oscillation Strouhal number on circular cylinder wake

The wake flow features and aerodynamic characteristics of a circular cylinder in an oscillating crossflow were experimentally investigated. The study focused on crossflow oscillation Strouhal numbers that were smaller than the natural wake vortex-shedding Strouhal numbers. Crossflow oscillations were generated using a downstream rotating plate method. The flow evolution processes were observed using laser-light sheet assisted smoke flow visualization technique. Wake instability and time-averaged velocities were assessed using a one-component hot-wire anemometer and particle image velocimetry. Pressure distributions on the cylinder's surface were quantified using a linear pressure scanner, obtaining pressure coefficient distributions and drag forces. The wake instability Strouhal number, velocity vectors, streamline patterns, and recirculation bubble geometries in the wake region of the circular cylinder were determined. The wake turbulence properties were analyzed using the triple-decomposition method, including turbulence intensities and Lagrangian integral length and time scales. The results of natural and oscillating crossflows were compared. The wake vortex-shedding Strouhal number was lower than the natural Strouhal number but higher than the crossflow oscillation Strouhal number. It was primarily influenced by the oscillation Strouhal number and the Reynolds number of the crossflow. Critical crossflow Reynolds and oscillation Strouhal numbers were identified, beyond which the wake vortex-shedding Strouhal number reached a constant value. The crossflow oscillation intensity did not significantly affect the wake vortex-shedding behavior. The study provided quantitative descriptions and discussions of recirculation bubble geometries and statistical turbulence properties. Furthermore, the crossflow oscillations led to a substantial reduction in the drag coefficient experienced by the circular cylinder.

Study on moving fire smoke characteristics and mechanical ventilation system of tunnel

Limited by the narrow space of the tunnel, fire has become one of the important factors threatening the safe operation of subway especially the fire on a moving vehicle. Researches on moving fire through the large length-width ratio of tunnels are extremely lacking at present. This study investigates the characteristics of moving fire and the influence of mechanical ventilation under different conditions. First, a three-dimensional model of the tunnel with the moving train is established, and the dynamic mesh simulation is conducted and validated by the experiments. Then, the variation of smoke temperature distribution under different fire source intensities, train speeds, and blocking ratios are studied. Based on the smoke flow characteristics, the mechanical ventilation with different layouts of draught fans is investigated. It is found that the maximum growth rate of smoke spread is 70.90% with an increase of two fans. Finally, the influence of the tunnel shaft on the smoke characteristics under different fire source locations is discussed. When the fire source is under the shaft, the smoke discharge efficiency reaches the highest, almost 5.89% and 21.91% higher than other conditions. This study provides the basis and reference for the research and control of the tunnel moving fire.

Exploring the Impact of Rapidly Actuated Control Surfaces on Drone Aerodynamics

This study investigates the use of rapidly actuated leading-edge and trailing-edge control surfaces to improve the control authority of small fixed-wing drones. Static and dynamic characteristics were investigated and presented in two separate papers. In this paper, the focus is on the dynamic effects observed from rapidly actuated 30% chord leading- or trailing-edge hinged control surfaces affixed to two flat-plate airfoils. Forces were resolved from surface pressure measurements and are augmented by PIV measurements, smoke flow visualization and analyses. The static study revealed that trailing-edge control surfaces exhibited higher effectiveness in producing time-averaged CL compared to leading-edge control surfaces. However, leading-edge control surfaces exhibit significantly less fluctuation in pressure and lift coefficients at fixed angles of attack and control surface deflections, indicating better stability. Unsteady aerodynamic effects of the airfoil at α=0∘ and “ramp” deflections of trailing- and leading-edge control surfaces from 0∘ to 40∘ with variations in actuation rates showed that CL peaks are approximately three to four times greater than static values for the case of the leading-edge control surface. This has significant implications for fixed-wing drone maneuverability and countering the effects of atmospheric turbulence.

Propeller Ground Effect in Forward Flight

The study of the fixed-pitch small-scale propeller in-ground effect is extended to forward flight conditions at different incidence angles of the propeller. Force-based experiments, smoke flow visualization, surface flow visualization, and phase-locked particle image velocimetry (PIV) indicate the presence of three distinct performance zones as a function of the advance ratio and ground distance, where the ground effect changes drastically. The power required at constant thrust shows an increasing trend after a threshold advance ratio for each and then decreases steeply upon a further increase in the advance ratio. Phase-locked PIV revealed the presence of a fountain vortex and a ground vortex at distinct for each distance that correlates with an increase in power and a decrease in thrust, respectively. At advance ratios below the onset of the fountain vortex lies the optimal ground effect zone. An increase in the advance ratio beyond this threshold will result in power increments due to the formation of the fountain vortex. A further increase in the advance ratio initiates the onset of the ground vortex where the ground effect is significantly reduced. The onset of the fountain vortex and the ground vortex occurs at comparatively lower advance ratios for propellers at a positive incidence angle. A normalization method is developed for ground effect forward flight that collapses the in-ground-effect performance for various normalized heights, advance ratios, and incidence angles.

Underground Evacuation and Smoke Flow Simulation in Guangzhou International Financial City during Fire

The underground space in the Starting Area in the Guangzhou International Financial City is being developed to save resources and improve land benefits. However, high-density development has increased the likelihood of fires. Therefore, PyroSim and Pathfinder were used in this study to investigate the fire smoke flow and personnel evacuation in the underground space in the Starting Area. Firstly, the 2D temperature cloud map and the temperature and visibility recorded by sensor A over time of Zone I in the Starting Area were analyzed. Then, the 3D smoke diffusion, the 3D temperature diffusion map, and the value of thermocouple and smoke obscuration recorded by sensors of Zone II were analyzed. Next, smoke flow of Zones III to V in the Starting Area under different fire source positions was simulated. Finally, the personnel evacuation model was established to simulate the personnel flow rate and density. The simulation results show that the available safe evacuation time for people is 530 s when all the firefighting facilities fail and fire breaks out in Zone I. For large public spaces, the overall spread speed of fire is fast, which requires the use of the fire control system in time to control the spread of fire. Fortunately, the space of evacuation time is relatively sufficient; it only takes 143 s to evacuate personnel safely in Zone II, which is sufficient compared to the time for the fire to completely spread. Suggestions were made for fire safety management, such as evacuating personnel to the safety exits of other adjacent areas during a fire and installing linkage fire alarm systems in large public space s.

Dispersion Simulations of Exhaust Smoke Discharged from Anchor-Handling Tug Supply Vessel under Various Wind Conditions

Exhaust smoke discharged from marine vessels and offshore plants not only contaminates the hull and cargo but is also the main cause of deterioration in the crew’s health and working environment. Rules and regulations have been implemented and have become stricter in recent decades. In this study, the exhaust smoke flow around an anchor-handling tug supply vessel in a stationary state, which has been seldom studied, is analyzed using computational fluid dynamics. The study investigates the effect of changing the wind speed and direction, which primarily affects the flow and dispersion of the smoke, to verify the suitability of the environment for the crew. To assess the environment, the recommended and comfortable concentrations of NO2 are used. The results demonstrate that a higher wind speed worsens the effect of the exhaust flow on the environment, owing to lower-pressure values and regions behind the structures. The emission of exhaust smoke is unsatisfactory when the wind flows from the side or rear of the vessel, instead of from the bow. Differing from previous studies conducted on general merchant vessels in navigating conditions, it was found that side winds can also have detrimental environmental effects in the stationary state. Adopting the original design of exhaust pipes leads to the distribution of exhaust smoke over the deck, exceeding the recommended exposure limit. Increasing the height of the pipes is identified as a simple but effective method to facilitate the smooth discharge of exhaust smoke.

Performance-Based Fire-Protection Design of Public Amenities with Restrained Personnel Activities

In this paper, performance-based fire-protection design is used for the fire-safety design of public amenities with restrained personnel activities. In these places, tourists’ activities are constrained in a limited space such as cockpit moving along the track. Since it is another typical scenario of fire-protection problem that cannot fully comply with the current mandatory codes and regulations, simulation analysis is used in order to ensure that such fire scenario could achieve performance objectives as expected. Firstly, corresponding fire-protection performance objectives, strategies and simplified evaluation criteria are brought forward in this paper. Then, through simulating the smoke flow in the fire using the computational fluid dynamics software FDS, the effectiveness of the smoke control strategy is verified. Meanwhile, the escaping environments of these fire scenes are analyzed. Further, the personnel evacuation simulation software (Pathfinder) is resorted to simulate the personnel emergency evacuation. The efficiency and the total time that consumed are obtained. Finally, by analyzing the similarities and differences of evacuation under different fire scenes, the fire and smoke spread in the riding area can be effectively controlled, and a safe evacuation environment can be provided for the evacuation of tourists.

The Contamination of the Lower Layer in Sloped Tunnel Fires

Fires in tunnels are a major concern due to the casualties they may cause. Therefore, forced ventilation is mandatory in long tunnels, despite the significant associated costs. In shorter tunnels, however, natural ventilation may be sufficient to comply with safety regulations. Accordingly, the analysis of natural fire smoke flow is relevant for tunnels shorter than 1000 m. This paper presents a computational investigation of the influence of the tunnel slope on the contamination of the cold lower layer with smoke and discusses how it impairs the user’s egress. Large-eddy simulations of the smoke propagation show three different regimes, namely, a quasi-horizontal tunnel behavior for a slope of 0.5%, a transitional behavior for slopes in the range of 1% to 5% and a quasi-forced ventilation behavior for a slope of 7%. The computational results are compared with the application of 1D equations to predict the upper layer temperature, the average mass flow rate, the upper layer mass flow rate, the upper layer velocity and the lower layer velocity. The distance from the fire to the location where the lower layer contamination with smoke starts is accurately predicted by the one-dimensional model for slopes of 2% and 3.5%. However, in the case of lower or higher slopes, the one-dimensional model performs poorly and needs further improvement.

Research on the Influence Mechanism of Outdoor Wind Environment on Indoor Smoke Exhaust Efficiency in the Super-High-Rise Tower Crown Based on Airpak Simulation

The high wind pressure and velocity of the outdoor environment make super-high-rise tower crown space distinct from general tall through space. This segregation causes the crown space to be particularly prone to smoke short-circuiting influenced by the outside wind environment if a fire occurs indoors, and causes deficient smoke exhaust efficiency in a fire. The goal of this study was to investigate the general principle regarding the effect of the outdoor wind environment on smoke exhaust efficiency of such spaces under the crown space. We measured external wind direction and wind pressure in the smoke exhaust in the tower crown and developed setting plans for the exhaust outlets and make-up air inlet. Airpak was used to create the external wind environment and compare simulations to see if smoke short-circuiting occurred. We analyzed the causes, summarized solutions that did not result in short-circuiting of smoke flow, and made adjustments. We provide an ideal plan for the setting direction and vent velocity of the make-up air inlet and exhaust outlet in the crown spaces of super-tall towers to improve the design of smoke exhaust systems in such spaces.

Experimental study of fire containment using water mist curtains in a reduced-scale deck of a ro-ro ship

Experiments have been conducted to evaluate the containment of smoke and heat using water mist curtains in a model setup of a ro-ro ship's cargo deck with a scale of 1:13, providing practical insights into the application of such fire protection systems in the cargo deck as well as valuable data for future numerical simulations. In this regard, the requirements of the international convention of Safety of Life at Sea (SOLAS) are studied for the side openings of so-called ‘open decks’ in comparison with ‘closed decks’, especially to examine the feasibility of using water mist curtains for creating isolated subdivisions in the ro-ro space as a fire management strategy. The water mist curtains are created with one or two rows of water mist nozzles at pressures ranging from 3 to 8 bar, while the source of smoke and heat is a liquid pool fire, and inert cargo items are used in some experiments. Correspondingly, the interaction between the water mist curtain(s) and the fire is evaluated in terms of its heat release rate, and the containment effect is quantified via measurements of smoke flow through the deck and through the windows, concentrations of gaseous species, as well as gas temperatures at various key locations. The study shows that water mist curtains have a strong effect on fire dynamics and smoke propagation, but containment is dependent on the configuration of side openings and the location of fire, among other important factors.

A novel approach for active and synchronous removal of fire-generated CO based on Co-La0.1 catalyst: From lab-scale to full-scale tests

CO is an invisible killer that severely threatens the safety of trapped personnel in fire disasters. The existing CO removal approaches are passive and ineffective, which could not satisfy the emergency rescue needs. An active and synchronous CO removal approach (ASCR) based on catalytic oxidation is proposed. By spraying dry powder extinguishant and catalyst powder, the isolation layer and oxidation layer are formed on the fuel surface. CO removal is achieved by both combustion suppression and CO oxidation methods. The synthesized Co-La0.1 catalyst exhibited superior catalytic activity, thermal stability, and selectivity, which met the application requirements of the ASCR approach. The results of lab-scall tests demonstrated that the CO concentration in the smoke flow decreased from 135 ppm to 0 ppm immediately once employing the ASCR approach. Full-scale tests in the confined tunnel further verified the practical application performance. With spraying 2 kg extinguishant and 0.9 kg catalyst powder, CO concentration increased merely by ∼ 20 ppm within 50 min, which was far lower than that without taking any disposal measures (∼800 ppm). This approach can effectively control the CO concentration below the safety threshold in fire disasters and is significant for emergency rescue.

Numerical study on the effects of blocking ratio and spraying angle on the smoke flow characteristics of new energy vehicle fires in tunnels

Compared with traditional fuel vehicle fires, new electric vehicle fires have a fast flame propagation rate and higher smoke toxicity. Thus, higher requirements need to be implemented when designing tunnel fire protection. In this study, a horizontal highway tunnel with a rectangular cross-section is taken as the research scenario, and the FDS numerical simulation method is used to study the effects of different blocking ratios and key parameters of the water mist system in a rectangular tunnel under longitudinal ventilation on the smoke temperature and flow state near the fire source area. The results indicate that the average velocity of smoke in the vicinity of the fire source in the tunnel is mainly related to the cross-sectional size of the obstruction, and changing the spray angle does not affect the state of the smoke flow field. The relationship between the cross-sectional size of the blocked vehicles in the tunnel and the spray angle is proposed. In addition, when the blocking ratio reaches 25%, the back-layer length of smoke corresponding to the subsequent blocking ratio remains basically unchanged. Setting a reasonable spray angle can significantly reduce the CO mass fraction in the tunnel, while the visibility of the tunnel will also decrease. Using the dimensionless analysis method, a critical velocity correction model based on the blocking ratio factors is proposed. These research results provide a theoretical reference for the design of longitudinal ventilation and smoke exhaust for new energy-electric vehicles in highway tunnels.

Impulse Fluid Simulation

We propose a new incompressible Navier-Stokes solver based on the impulse gauge transformation. The mathematical model of our approach draws from the impulse-velocity formulation of Navier-Stokes equations, which evolves the fluid impulse as an auxiliary variable of the system that can be projected to obtain the incompressible flow velocities at the end of each time step. We solve the impulse-form equations numerically on a Cartesian grid. At the heart of our simulation algorithm is a novel model to treat the impulse stretching and a harmonic boundary treatment to incorporate the surface tension effects accurately. We also build an impulse PIC/FLIP solver to support free-surface fluid simulation. Our impulse solver can naturally produce rich vortical flow details without artificial enhancements. We showcase this feature by using our solver to facilitate a wide range of fluid simulation tasks including smoke, liquid, and surface-tension flow. In addition, we discuss a convenient mechanism in our framework to control the scale and strength of the turbulent effects of fluid.