开放空气环境中的池火灾及其危险性分析

本文涉及开放空气环境中池火灾及其危险性分析，对池火灾的如下物理特征进行了总结；（１）火焰的几何形状及尺寸；（２）火焰表面的热辐射通量；（３）热辐射的传播，文中并归纳了热辐射的各种破坏准则，推导了进行池火灾危险性分析的程序和算法，通过数值模拟计算，讨论了一些重要规律。     

Comparative analysis on temperature characteristics of hydrogen-powered and traditional fossil-fueled vehicle fires in the tunnel under longitudinal ventilations

Vehicle fires in the tunnel are a great threat to the safe operation of the tunnel. Due to the rapid development of the hydrogen economy, the fire due to the hydrogen leakage could not be avoided and may bring great damage to the passengers and infrastructure. Due to the large difference between pool fires of traditional fossil-fueled and jet fires of hydrogen-powered vehicles, it is in doubt whether the existing longitudinal ventilation design could still be effective for the safety issue of hydrogen powered vehicles. To solve this problem, it is necessary to compare temperature characteristics of hydrogen-powered and traditional vehicle fires with and without longitudinal ventilations. In present work, we conducted a numerical investigation to discuss the different temperature distributions of traditional and hydrogen-fueled vehicle fires. Results indicate that the high temperature zone of the pool fire only exists above the ceiling of the vehicle. For hydrogen-powered vehicle fire, the high-speed hydrogen jet with the strong inertial force could push the hot smoke flows back to the ground. The ceiling temperature of hydrogen-powered vehicle fire is larger since hydrogen-powered vehicle has a larger heat release rate and the fire hazard of jet fires bring more danger compared with the pool fire. Although the temperature stratification is also obvious for the hydrogen-powered vehicle fire, the air temperature in the lower region could be heated and still high enough to bring a great damage to the passengers’ lives. This is quite different with the traditional pool fire. In addition, the critical ventilation velocity is also discussed. The theoretical equation could well predicted the critical ventilation velocity of traditional vehicle fires. For hydrogen-powered vehicle fires, the critical ventilation velocity could reach up to 6 m/s. The theoretical equation could not well predict the critical ventilation velocity of hydrogen-powered vehicle fires due to exist of hydrogen jet fires.     

Investigating the effect of computational grid sizes on the predicted characteristics of thermal radiation for a fire

Recently, the phenomenological modeling of fires has been shifted from the engineering application of correlation-based methods to the computational fluid dynamics (CFD) techniques. Therefore, the majority of this paper is to investigate the effects of grid sizes on the predicted radiative characteristics involved in a fire using CFD simulations, with the aim of selecting the appropriate grid size under the consideration of prediction accuracy and computing cost. Based on the present simulations, the predicted flame height increases as the decreasing grid size and would approach to a quasi-steady value if the simulation grids are adopted to be small enough. Similar results are also revealed in the radiative heat flux behaviors. The predicted distributions of radiative heat fluxes have no significant variations as the grid size is reduced to some small value. Several experiments of small pool fires with various diameters (20–38 cm) are conducted to assess the present CFD predictions. Using the appropriate grid size, the predicted results for radiative heat fluxes and flame heights show good agreement with the experimental data for different-size pool fires. This grid size suggested in this paper could assist the CFD simulations of pool fires in obtaining the accurate enough predictions with reasonable computing time.     

航空发动机转子叶片损伤评定实验研究

针对发动机叶片损伤的评定,通过低压压气机二级转子叶片的涡流激振试验,在叶片振动状态下用扫频法测试叶片一阶固有频率;在叶片进气边不同位置预制不同半径的损伤,得到了不同损伤位置、损伤半径下叶片一阶固有频率,并利用BP神经网络方法对损伤和评定参数之间的非线形关系进行了评定,初步验证了理论分析结果,进行了损伤预测。     

Pool fire dynamics: Principles,models and recent advances

Pool fire is generally described as a diffusion combustion process that occurs above a horizontal fuel surface (composed of gaseous or volatile condensed fuel) with low (∼zero) initial momentum. Fundamentally, this type of diffusion combustion can be represented by basic forms ranging from a small laminar candle flame, to a turbulent medium-scale sofa fire, and up a storage tank fire, or even a massive forest fire. Pool fire research thus not only has fundamental scientific significance for the study of classical diffusion combustion, but also plays an important role in practical fire safety engineering. Therefore, pool fire is recognized as one of the canonical configurations in both the combustion and fire science communities. Pool fire research involves a rich, multilateral, and bidirectional coupling of fluid mechanics with scalar transport, combustion, and heat transfer. Because of the unabated large-scale disasters that can occur and the numerous and complex 'unknowns' involved in pool fires, several new questions have been raised with accompanying solutions and old questions have been revisited, particularly in recent decades. Significant developments have occurred from a variety of different perspectives in terms of pool fire dynamics, and thus the scientific progress made must be summarized in a systematic manner. This paper provides a comprehensive review of the basic fundamentals of pool fires, including the scale effect, the wind effect, pressure and gravity effects, and multi-pool fire dynamics, with particular focus on recent advances in this century. As the fundamentals of pool fires, the theoretical progress made with regard to burning rates, air entrainment, flame pulsation, the morphological characteristics of flames, radiation, and the dimensional modelling are reviewed first, followed by new insights into the fluid mechanics involved, radiative heat transfer and combustion modeling. With regard to the scale effect, recent experimental and theoretical advances in internal thermal transport and fluid motions within the liquid-phase fuel, lip height effects, and heat transfer blockage are summarized systematically. Furthermore, new understandings of aspects including heat feedback and the burning rate, flame tilt, flame length and instability, flame sag and base drag, and soot and radiation behavior under wind, pressure and gravity effects are reviewed. The growing research into the onset and the merging dynamics of multiple pool fires in the last decade is described in the last section, this research will be helpful in the mitigation of threatening outdoor massive (group) fires. This review provides a state-of-the-art survey of the knowledge gained through decades of research into this topic, and concludes by discussing the challenges and prospects with regard to the complex coupling effects of heat transfer, with the fluid and combustion mechanics of pool fires in future work.     

Experimental Study on the Interaction of Fine Water Spray with Liquid Pool Fires

InhoductionThe use of Ane water spray tO suPPress andextingush fires is one POtential candidate for halonrePlat. APPlications CUrrently indsde thesuPPression of dust exPlosion, solid and liquld fuelcOmbushon wdri cotheed sPaces, and fire withineleCtrical panels and so on. Fine wate sPray may Providemor effeehve fire sUPPrssion than new gaseousflooding agats in aPPlications such as deeP-seated thes,Where the coollng caPwi and penethaon of watedropets reach the base of fires. Another …     

矩形油池火羽流中心线的温度分布

开展了不同火源形状因子(1≤s≤3)的较大功率矩形油池火实验,测量了燃料的质量损失速率,借助编制的图像分析程序处理实验视频得到了连续火焰最大高度(Lc)和火焰最大高度(Lm).将Hasemi羽流中心线温度修正模型的理论预测值和实验值进行了对比,结果表明,随着s的增大,Hasemi理论模型预测值呈现增大的趋势,s=1时,理论预测值和实验值比较接近,两者无明显差异性;s=1.33和s=3时,理论预测值和实验值的变化趋势一致,但两者的总体偏差超过5%.     

600MW超临界机组高温氧化皮问题的探讨

论述了600MW超临界机组高温氧化皮的生成及危害,对检测和清理高温氧化皮的方法进行了介绍,探讨了高温氧化皮受控剥落的可能性,提出来彻底解决高温氧化皮的方向。     

Security risk analysis of a hydrogen fueling station with an on-site hydrogen production system involving methylcyclohexane

Although many studies have looked at safety issues relating to hydrogen fueling stations, few studies have analyzed the security risks, such as deliberate attack of the station by threats such as terrorists and disgruntled employees. The purpose of this study is to analyze security risks for a hydrogen fueling station with an on-site production of hydrogen from methylcyclohexane. We qualitatively conducted a security risk analysis using American Petroleum Institute Standard 780 as a reference for the analysis. The analysis identified 93 scenarios, including pool fires. We quantitatively simulated a pool fire scenario unique to the station to analyze attack consequences. Based on the analysis and the simulation, we recommend countermeasures to prevent and mitigate deliberate attacks.     

Modeling and evaluating the effect of forest fire control on the CO2 cycle in Siberia

The forests of Siberia play an important role in absorbing carbon dioxide. Resent increases in forest fires, due to both human negligence and global warming, appear to cause significant damage to the forests. In the present research, basic models were established to evaluate changes in land area and carbon flux by forest fires and by disturbances of permafrost. Basic data necessary for the analysis are also summarized and presented. The characteristic of the model is a solution to the problem with probabilities in statistic space, rather than detailed simulation. The results of the simulation shows the significance of forest fires on the net carbon flux, which maintains the present level with a sensitive balance between large positive and negative fluxes. It was also shown that forest areas keep decreasing over a thousand-year time span even after a fire rate becomes constant. This implies that changes of land features are quite slow and that there may be irreparable situations at the time when changes are actually recognized. The effect of fire control and planting of the areas exposed to fires is also evaluated.     

Balancing fatigue damage and turbine performance through innovative pitch control algorithm

Improvements to current pitch control strategies are explored by analysing the addition of a dynamic peak‐shaving algorithm, called the load limiting algorithm (LLA). The goal of this dynamic peak‐shaving algorithm is to reduce blade fatigue damage caused by wind gusts without sacrificing energy capture. This paper introduces a multivariate procedure based on the Taguchi method to systematically test different controller configurations and evaluate the algorithm's effectiveness. The LLA was tested through numerical analysis and field experiments. Numerical studies were performed on the Controls Advanced Research Turbine (CART) and the National Renewable Energy Laboratory (NREL) 5 MW model. Field testing was conducted on the CART. The primary metrics of LLA effectiveness were blade fatigue damage, measured in 20 year damage equivalent loads (DEL) for root flap bending and annual energy production (AEP). Numerical results indicate a reduction in weighted flap bending DEL (Flap DEL) for both turbine platforms. The CART demonstrates a reduction of 3.2% with a half‐percent loss in AEP. The LLA is markedly more effective on the NREL 5 MW, demonstrating a reduction of 5–9% in Flap DEL with a drop of 1–3% in AEP. Secondary benefits such as DEL reductions for other components, operating extreme blade loads, and pitch duty cycle were also explored.Copyright © 2011 John Wiley & Sons, Ltd.     

A fully-coupled simulation of vortical structures in a large-scale buoyant pool fire

A numerical study simulating the temporal vortical structures of a large-scale buoyant pool fire has been carried out using a fully-coupled Large Eddy Simulation (LES) model which incorporates all essential subgrid scale (SGS) turbulence, combustion, radiation and soot chemistry considerations. Based on the strained laminar flamelet approach, a scalar dissipation conditioned SGS combustion model is introduced to distinguish the highly non-equilibrating burn and extinguishment of flamelets commonly found in pool fires. Numerical results from the present model are validated and compared against a one-meter diameter methane pool fire experimental data and predictions from other LES field models. The predicted time-averaged velocity and temperature profiles have been found to be in good agreement with the experimental data and those numerical results. Qualitative comparisons of instantaneous velocity field against experimental data have revealed that the dynamic phenomena of large-scale vortical structures and its associated puffing behaviour of pool fire are well captured. Quantitative comparisons of velocity time history and pulsation frequency also show close agreement against experimentally evaluated quantities.     

Heat transfer in pool fires at a certain small lip height

Under the assumptions of a gray-diffuse and homogeneous disk flame at the top plane of the vessel, a diffuse-gray fuel and vessel wall surfaces, and a transparent medium in the ullage space of the vessel, the longitudinal temperature and heat flux distributions at the vessel wall surface for ethanol and kerosene pool fires were calculated numerically. The calculations were performed using the data of Rasbash et al. The emissive power of the disk flame assumed at the top plane of the vessel, which is determined from the heat balance in the combustion system, is approximately equal to the mean values of the radiative flux measured near the top plane of the vessel in the similar fuel type and pool size at the relatively small lip height. The calculated emissive power of the assumed disk flame decreases with time and approaches the asymptote, depending on the depth of the vapor zone. The heat of evaporation and the rate of increase of the sensible heat of the liquid increases and decreases, respectively, with time and approach asymptotes. The time evolution of the sum of them is similar to that of the emissive power of the disk flame derived from the heat balance in the combustion system. Even in relatively small lip heights and low emissive power flames, as in non-hot-zone-forming pool fires, the rates of heat transfer between the wall and the ambient fluids are large, and cannot be neglected in comparison to the heat input from above to the fuel surface.     

Modeling a fire whirl generated over a 5-cm-diameter methanol pool fire

We conducted a series of laboratory-scale fire whirl experiments spinning 5-cm-diameter methanol pool fires and observed elongated flame height compared with the pool fire without spin. A simple scaling analysis was conducted to obtain dependency of the axial flame height on the momentum-controlled circulation and the effect of buoyancy. To obtain a specific functional relationship for the parameters obtained by the scaling analysis, we developed an analytical model consisting of coupled species and energy equations and Burgers vortex for circulation generated by a fire whirl. The solution of the coupling equations shows that the average rate of heat transfer from the flame to the fuel surface is a function of the vortex core radius; a smaller vortex core radius provides more heat to the fuel surface enhancing evaporation thereby producing the longer flame height. This new model predicts both flame height and flame shape. The flame height prediction compare favorably with results from the scaling analysis and experiment.     

钝体绕流及其燃烧特性的研究

在火灾中常见到一些钝体可燃物，与迎风面相比，其北风面烧毁的程度要严重得多，以及仅在背风面有过火痕迹等燃烧现象，如森林火灾中的树干，建筑火灾中的柱体也有类似问题本文针对这些火灾特性，进行了钝体绕流及其燃烧特性的实验和计算机模拟研究，并对这一现象进行了分析。     

细水雾与液体燃料火焰相互作用的小尺度实验研究及简化模型

细水雾灭火技术是可以替代哈龙灭火剂的绿色灭火技术。以此为工程背景,开展了细水雾与液体燃料火焰相互作用的小尺度实验研究,结果表明:预燃时间、喷雾气压、细水雾气源种类等参数对灭火过程有重要影响。细水雾抑制熄灭液体燃料火焰的主要机理是燃料表面冷却效应。建立的液体燃料平均温度零维简化模型与实验结果吻合较好。     

Burning rates of liquid fuels in fire whirls

This paper presents semi-empirical investigations on the quasi-steady burning rates of laminar and turbulent fire whirls established over liquid fuel pools. The inflow boundary layer above the fuel surface consists of two regions: outer reactive region and inner non-reactive region. Based on the momentum boundary layer solutions with the applications of stagnant film model and Chilton–Colburn analogy, the burning rates are correlated with ambient circulation and pool size for laminar and turbulent fire whirls respectively. It is shown that in general pool fires the mass and heat transfers on the fuel surface are controlled by natural convection, while in fire whirls they are strongly enhanced by forced convection. Fuel evaporation rate in the outer region is relatively larger than that in the inner region. The large proportion of fuel evaporated from the outer region is mainly due to its larger area. The predictions agree well with the data from the present experiments and the literature. Furthermore, the flame height is confirmed to be proportional to the ambient circulation for both laminar and turbulent liquid fire whirls.     

甲醇燃料火焰可见度的研究

甲醇火焰可见度低,因此就带来了使用中的安全性问题.作者采用一种实验室方法,对火焰的照度进行测量,从而提供了甲醇燃料火焰可见度的评估基础.对甲醇、柴油、汽油、正庚烷、异辛烷、甲苯及甲醇混合燃料共十二种燃料进行了研究,提供了不同燃料的火焰高度、燃烧速度及火焰照度的定量结果.纯甲醇火焰的照度约为汽油的千分之一,用汽油作添加剂可以提高甲醇火焰的照度,但在燃烧过程中随汽油的蒸发而照度下降.作者建议用着火一分钟后,测量期2秒内照度的平均值L与标准偏差σ的和L+σ作为评价可见度的参数.     

A smart rotor configuration with linear quadratic control of adaptive trailing edge flaps for active load alleviation

The paper proposes a smart rotor configuration where adaptive trailing edge flaps (ATEFs) are employed for active alleviation of the aerodynamic loads on the blades of the NREL 5 MW reference turbine. The flaps extend for 20% of the blade length and are controlled by a linear quadratic (LQ) algorithm based on measurements of the blade root flapwise bending moment. The control algorithm includes frequency weighting to discourage flap activity at frequencies higher than 0.5 Hz. The linear model required by the LQ algorithm is obtained from subspace system identification; periodic disturbance signals described by simple functions of the blade azimuthal position are included in the identification to avoid biases from the periodic load variations observed on a rotating blade. The LQ controller uses the same periodic disturbance signals to handle anticipation of the loads periodic component. The effects of active flap control are assessed with aeroelastic simulations of the turbine in normal operation conditions, as prescribed by the International Electrotechnical Commission standard. The turbine lifetime fatigue damage equivalent loads provide a convenient summary of the results achieved with ATEF control: 10% reduction of the blade root flapwise bending moment is reported in the simplest control configuration, whereas reductions of approximately 14% are achieved by including periodic loads anticipation. The simulations also highlight impacts on the fatigue damage loads in other parts of the structure, in particular, an increase of the blade torsion moment and a reduction of the tower fore‐aft loads. Copyright © 2014 John Wiley & Sons, Ltd.     

Human health-related externalities in energy system modelling the case of the Danish heat and power sector

This paper discusses methodology of energy system modelling when reduction of local externalities, such as damage to the human health from energy production-related air pollution, is in focus. Ideally, the local energy externalities should be analysed by adopting the impact pathway approach of ExternE study, and following the pollutants from their release to the personal uptake and resulting health effects. This would require inclusion of air pollution modelling and monetary valuation of the impacts into an energy system optimisation process. However, this approach involves a complex study and generalisations are needed.