CFD modelling of the effect of fire source geometry and location on smoke flow multiplicity

Understanding solution multiplicity of smoke flow at the same building configuration and ambient conditions is important for managing smoke flows and human evacuation in buildings. One of the known examples with solution multiplicity is in a simple single-compartment building on fire under an opposing wind. The occurrence of multiple solutions of smoke flow is induced by competing wind and thermal buoyancy forces. Under a given and moderate wind, the critical buoyancy flux ratio for the existence of smoke flow multiplicity, which is a ratio between defined parameters representing buoyancy force and wind pressure, is related to building height and opening area, as shown using a zone model. Computational fluid dynamics (CFD) simulations were used here to evaluate whether the behaviour of smoke flow multiplicity was affected by the geometry and location of the fire source(s). Our simulation results were in good agreement with previous macroscopic analysis results. A floor fire source can produce the largest smoke flow rate in the buoyancy-dominated flow regime among the tested cases while two corner sources can produce the smallest smoke flow rate. A floor source had a relatively large smoke flow rate in the wind-dominated flow regime while a point source had relatively small smoke flow rate. Moreover, a larger critical buoyancy flux ratio and a larger range of fire power in which smoke flow multiplicity existed were found for a floor fire source than for other sources. Switching of smoke flow solutions in building fires was found to depend on the initial conditions and the magnitude of flow perturbations.     

Influence of cell geometry and mesh resolution on large eddy simulation predictions of flow around a single building

A number of research studies have employed a wide variety of test conditions to numerically assess flow field around buildings. In such studies, the employed mesh system and its resolution played a crucial role in determining the ultimate degree of solution accuracy. The objective of this study is to better establish a quantitative assessment of the influence of cell geometry and mesh resolution on the numerical predictions of large eddy simulation (LES) of the flow field around a single building. In order to achieve this objective, a number of mesh styles including conventional hexahedral-based mesh, tetrahedral-based mesh, and prism-based mesh have been considered. In addition, hybrid meshes of tetrahedron and hexahedron cells are also considered. In each mesh style, four grid resolutions were investigated: coarse, medium, fine, and very fine. Accuracy of the simulation has been assessed by applying comparisons to the experimental data available in literature. Moreover, quantitative grid convergence was calculated based on the grid convergence index, which accounts for the degree of grid refinement. Future studies are needed to analytically evaluate the influence of cell geometry on the solution accuracy and to more precisely evaluate other grid system options including various forms of hybrid configuration meshes.     

The effects of simulated fire pressure and outside wind on the internal pressure distribution in a five-storey model building

This paper presents some of the wind tunnel pressure measurements made on a five-storey model building (32 cells), with a vertical shaft and fixed leakage characteristics. Internal and external pressures measurements are presented for various wind angles and a simulated fire pressure in a room on floor 2 and floor 4. Comparison is made to assess the effect of fire on internal pressure distribution. Although the results are presented for all the wind angles investigated, a detailed discussion is confined only to a single wind angle. Implications of the combined effect of wind and fire on the shaft pressurization system design calculations must take these two factors into account.

In a fire situation it is possible that escapers may leave some of the shaft doors open or the fire room door may burn down. In such a case the pressurization system can become ineffective, causing escape routes to get smoke-logged. The effect of a combination of fire door openings was also investigated. The results for the following door opening combinations are presented and discussed:

1. (i) shaft door open alone;

2. (ii) fire room door open alone;

3. (iii) shaft and fire room doors open together.

It is shown quite clearly that these openings are significant for a range of wind angles.     

Inflow turbulence generation techniques for large eddy simulation of flow and dispersion around a model building in a turbulent atmospheric boundary layer

The present paper investigates the performance of various inflow turbulence generation techniques (ITGT) for large eddy simulation (LES) of flow and dispersion around a model building in a turbulent atmospheric boundary layer. Four different ITGT comprising 1 – no fluctuations, 2 – spectral method, 3 – vortex method and 4 – internal mapping, based on two basic methodologies (i.e. precursor and synthetic turbulence methods), are employed. These techniques are evaluated by considering their prediction accuracy, computational costs, complexity of implementation, inflow information required to operate and impacts on the flow downstream of the inlet, particularly in the wake region of the model building. Results indicate that the accuracy of LES predictions is greatly reliant on ITGT. It is shown that ITGT not only have significant effects on flow field vortical structures, but also influence frequency contents of velocity fluctuations, recirculation regions and plume shapes in the wake region.     

Simulation of air flow in the IEA Annex 20 test room—validation of a simplified model for the nozzle diffuser in isothermal test cases

The modeling of air supply devices has been identified from the International Energy Agency (IEA) Annex 20 project as one of the most important problems in applying computational fluid dynamics (CFD) to predict air flow pattern and air distribution in buildings, and the complicated HESCO nozzle diffuser used in the IEA Annex 20 test room has been proved to be particularly difficult to model. In a previous study, a simplified model for this diffuser was developed and validated against experimental data. It has been shown that this model can yield good prediction for the wall jet flow issued from the diffuser, but whether this model is capable of correctly predicting the global flow pattern in the whole test room was not known. In this paper, the benchmark data of the IEA Annex 20 Test Cases B2 and B3 were used to evaluate the performance of the model for the prediction of the global air flow pattern in the test room. It was demonstrated that this model can predict the air flow pattern in the whole test room for both the Test Cases B2 and B3 with reasonable accuracy. The significance of a velocity correction when comparing the numerical prediction with experimental data obtained using omni-directional anemometers was also discussed.     

Indicators for the evaluation of wind tunnel test section flow quality and application to a numerical closed-circuit wind tunnel

The flow in a wind tunnel test section must meet high standards to obtain accurate and reliable measurement data. Good flow quality demands a certain degree of spatial uniformity and temporal steadiness of velocity and pressure. In this paper, a set of six new indices is developed and presented that relate spatial aspects of the mean velocity field to flow quality. One index quantifies the degree of uniformity of the velocity field and can be used directly as a flow quality indicator. The five other indices are related to different types of deviations from spatially uniform flow; skewed flow and angularity (up-flow and down-flow, swirl, cross-flow, diverging and converging flow). The indices can be used to evaluate the flow quality in existing tunnels, to assess the impact of design modifications, as well as to carry out CFD-based design of new wind tunnels. As an example, the indices are applied to assess the impact of guide vanes and screens on the test section flow quality in a numerical closed-circuit wind tunnel.     

世贸大楼的人群疏散案例给计算机模拟技术的启示

计算机模拟技术已成为研究人群疏散问题的有效技术手段，也是该领域目前的发展方向。但是，人群疏散行为和模型的建立是一个重要前提。从真实火灾中获得人群疏散行为的规律对于建立合理的人群疏散行为模型是非常重要的。美国纽约世贸大楼的两次人群疏散的真实案例，正好可以提供这样的帮助。     

从风环境试验看建筑群对自身风环境的影响：深圳福田同城建筑风洞风 …

本文作者从建筑风环境的试验目的和评价标准出发，以试验原始数据为基础，对自成一个建筑群的深圳福田商城的风洞风环境试验结果进行了分析。     

底模和养护条件对砂浆强度影响的对比试验研究

通过工地制作各种底模条件下的试块,对砂浆试块进行了抗压试验,并对试验结果进行了分析,同时进行了底模和养护条件对砂浆强度影响的对比研究,得出了有价值的结论。     

Experimental study of the effects of a thermal plume entrainment mode on the flow structure: Application to fire

The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free thermal plume was examined by generating a plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the plume. We then determined the structure of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume.     

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

CFD模拟在某游泳馆通风空调设计中的应用

在杭州某游泳馆通风空调设计中，为了考察围护结构内表面的结露情况，利用简化的模型进行了CFD数值模拟。本文介绍了这次数值模拟过程，并根据模拟结果分析比较了设计相对湿度不同的两个方案，模拟结果显示，设计相对湿度较小的方案比较经济。本文的模拟结果也可为类似工程的空调设计方案选择提供一定的参考。     

Correction to: Deformation characteristics,mechanisms, and influencing factors of hydrodynamic pressure landslides in the Three Gorges Reservoir: a case study and model test study

Bulletin of Engineering Geology and the Environment - A Correction to this paper has been published: https://doi.org/10.1007/s10064-021-02152-2     

Using a linked soil model emulator and unsaturated zone leaching model to account for preferential flow when assessing the spatially distributed risk of pesticide leaching to groundwater in England and Wales

Although macropore flow is recognized as an important process for the transport of pesticides through a wide range of soils, none of the existing spatially distributed methods for assessing the risk of pesticide leaching to groundwater account for this phenomenon. The present paper presents a spatially distributed modelling system for predicting pesticide losses to groundwater through micro- and macropore flow paths. The system combines a meta version of the mechanistic, dual porosity, preferential flow pesticide leaching model MACRO (the MACRO emulator), which describes pesticide transport and attenuation in the soil zone, to an attenuation factor leaching model for the unsaturated zone. The development of the emulator was based on the results of over 4000 MACRO model simulations. Model runs describe pesticide leaching for the range of soil types, climate regimes, pesticide properties and application patterns in England and Wales. Linking the MACRO emulator to existing spatial databases of soil, climate and compound-specific loads allowed the prediction of the concentration of pesticide leaching from the base of the soil profile (at 1 m depth) for a wide range of pesticides. Attenuation and retardation of the pesticide during transit through the unsaturated zone to the watertable was simulated using the substrate attenuation factor model AQUAT. The MACRO emulator simulated pesticide loss in 10 of 12 lysimeter soil-pesticide combinations, for which pesticide leaching was shown to occur and also successfully predicted no loss from 3 soil-pesticide combinations. Although the qualitative aspect of leaching was satisfactorily predicted, actual pesticide concentrations in leachate were relatively poorly predicted. At the national scale, the linked MACRO emulator/AQUAT system was found to predict the relative order of, and realistic regional patterns of, pesticide leaching for atrazine, isoproturon, chlorotoluron and lindane. The methodology provides a first-step assessment of the potential for pesticide leaching to groundwater in England and Wales. Further research is required to improve the modelling concept proposed. The system can be used to refine regional groundwater monitoring system designs and sampling strategies and improve the cost-effectiveness of the measures needed to achieve 'good status' of groundwater quality as required by the Water Framework Directive.     

A simple stepwise method to determine and evaluate the initiation of tertiary flow for asphalt mixtures under dynamic creep test

A number of research studies have focused on the linkage between material properties and pavement performance. Part of the efforts in this research was the development of Superpave simple performance tests (SPT). One of the Superpave SPT is the repeated loading or dynamic creep test. The output of this test is the flow number, which is the initiation of tertiary flow. A common method in examining the flow number is to locate the lowest point in the strain rate versus cycle number curve, or the minimum value of the strain rate. However, this method may provide confusion due to the variation in the test data. Researchers have been trying to discover new effective methods for determining flow number. Their efforts have led to the development of several excellent approaches. However, these methods need to be more refined in order to improve the user-friendliness to engineers, researchers, and even students. A new simple stepwise method was developed and evaluated in this paper. In this process, it was assumed that the strain would only be maintained at the same point or increased over the load cycle number. Then, the flow number at the minimum point of new strain rate versus cycle number was determined. The flow number results from this new method are simpler and more practical compared to other methods for determining the flow number. In addition, the rate of deformation at the secondary stage was correlated well with the flow number using this method.     

A computer model for estimating the response of sprinkler links to compartment fires with draft curtains and fusible link-actuated ceiling vents

A computer program, LAVENT, is now available which computes the heating of fusible links due to the presence of a ceiling jet imbedded in an upper layer. An important new feature in this program is that the two-dimensional structure of the ceiling jet is taken into account such that the location of the link beneath the ceiling plays a role in the response of the link. The links can be used to activate ceiling vents such that the effect of venting the upper layer on the ceiling jet may be studied. Additional applications would include the study of upper layer containment through the use of a combination of draft curtains and ceiling vents. The geometry modeled by the program is that of a large compartment enclosed by a combination of walls and draft curtains.     

Deformation characteristics,mechanisms, and influencing factors of hydrodynamic pressure landslides in the Three Gorges Reservoir: a case study and model test study

Bulletin of Engineering Geology and the Environment - Hydrodynamic Pressure landslides are the most typical landslides affected by the water level in the Three Gorges Reservoir. These types of...     

Use of continuous simulation model (COSIMAT) as a complementary tool to model sewer systems: a case study on the Paruck collector,Brussels, Belgium

Episodic Combined Sewer Overflow (CSO) discharges effectively control the ecological status of receiving water bodies. Hydrodynamic models like the Storm Water Management Model (SWMM) are often used to model the CSO events. However, such detailed models are computationally demanding especially when a long‐term simulation of a complex system is required. Considering this, we developed an alternative simple continuous simulation model (COSIMAT) using the SIMULINK? module in MATLAB? as a means of solving the issue of computational time associated with the detailed models. The COSIMAT model was tested against a detailed model set up on the SWMM. The Paruck collector – one of the major Collector of the Brussels’ sewer system was used as an example case. Results showed that the accuracy of the simplified COSIMAT model was comparable to that of the detailed hydrodynamic model (SWMM) with a significant reduction of computational time by a factor of 8. We believe such alternative approaches would be useful to replace a computationally demanding model component of an integrated modelling system of a complex sewer system.     

A continuous flow bioassay method to evaluate the effects of outboard motor exhausts and selected aromatic toxicants on fish

A continuous flow bioassay system was designed to measure the effects of outboard motor exhaust (OME) emissions and selected volatile and evaporative aromatic toxicants on goldfish (Carassius auratus). Continuous flow bioassays were run for 24, 48, 72, 96, and 720 h to determine lethal concentrations for 50% of individuals (LC-50's) for leaded OME, non-leaded OME, toluene, xylene, and 1,3,5 trimethylbenzene, the three individual compounds having been identified as significant aromatic components of OME. The 96 h LC-50's for these substances were found to be 171, 168, 23, 17, and 13 ppm, respectively. The values of 171 and 168 ppm for the two OME's are given in terms of gallons of fuel burned per million gallons of water. The continuous flow bioassay method was demonstrated to be a more reliable indicator of the effects of OME pollutants on aquatic organisms than is the static bioassay method.