【作者】 李林书；

【导师】 王顺喜； 辛喆；

【作者基本信息】 中国农业大学 ， 机械设计及理论， 2014， 博士

【摘要】 风力灭火机为我国草原防火主流灭火设备。本文将空气引射技术应用于风力灭火机,改变了风力灭火机喷风筒出口后流场结构,改善了出口风量同时增大了有效灭火距离。本文首先通过对无扩压亚音速空气引射风力灭火机的出口后流场基本模型的研究确定了出口后1.5m风速,1.5m处有效灭火面积及有效灭火距离为评价风力灭火机气动性能好坏的标准,并对这三个指标进行了方程推导,提出了有效灭火面积比的概念。建立了引射式风力灭火机及涡喷式引射风力灭火机的CFD模型,通过试验对比的方法确定了适合计算引射式风力灭火机内部流场湍流模型为RNG κ-ε,适合计算涡喷式引射风力灭火机内部流场湍流模型为S-A模型。用试验的方法确定了两种风力灭火机CFD模型的边界条件。用试验的方法测定了混合室出口截面速度不均匀度β,并找到了β与用于计算2种风力灭火机出口后流场的湍流系数a的拟合关系式。证明了在所研究范围内其这2种拟合关系式的有效性。应用CFD方法研究混合室直径Dm、混合室长度Lm、喷嘴位置S及接收室收敛角θ对引射式风力灭火机性能指标单一因素影响,发现其影响程度顺序为：Dm>Lm>S>θ。分析不同参数组合的245组CFD模型发现,Dm、Lm、θ三个尺寸参数存在较强交互性影响。制造了引射式风力灭火机并进行了性能指标试验测试,结果为：对比于传统便携式风力灭火机,距离喷射筒出口1.5m速度u1.5提高了8.31%,有效灭火距离Lc提高了9.95%,1.5m处有效灭火面积而Ac提高了62.2%。应用CFD分析的方法发现单一因素对涡喷式引射风力灭火机性能指标的影响大小顺序为：Dm>S>Lm>θ。其中Lm和θ的单独变化对涡喷式引射风力灭火机性能指标影响非常小。分析不同参数组合的486组CFD模型发现,Dm、S、θ三个尺寸参数对涡喷式引射风力灭火机性能指标存在着交互性影响。最终确定最优尺寸参数组合为：混合室直径Dm为80mm,接收室收敛角θ为20°,喷嘴位置S为0,混合室长度为Lm为700mm。应用该参数组合制造的喷射筒实测值为：u1.5为42.7m/s,Lc为3.16m,Ac为0.091m2。其最大误差绝对值小于4.39%。说明应用响应曲面及CFD分析的方法计算涡喷式引射风力灭火机流场是有效的。根据受力分析及国家标准,确定了涡喷式引射风力灭火机基本结构及尺寸。制造了涡喷式引射风力灭火机并进行了整机性能评测,发现除噪声大于规定标准将外,其它指标均大幅优于便携式风力灭火机整机性能标准。进行了草原实地风力灭火试验并将试验数据与便携式风力灭火机进行了对比。发现涡喷式引射风力灭火机能够处理更高火强度及可燃物密度草原火,且灭火时间低于便携式风力灭火机,同时其抗复燃性也优于便携式风力灭火机。更多还原

【Abstract】 Portable pneumatic extinguisher is an effective device which has been widely used for forest and grassland fire extinguishing in China. In order to enhance the effective range and rate of discharge of portable pneumatic extinguisher, a new method to weaken air velocity attenuation by increasing the flow rate using an air ejector is proposed and investigated in this study. This research belongs to the category of subsonic air ejector.Firstly, tow types of turbulivity of air jet’a’has been expressed by the non-uniformity of flow velocity distributions on. It’s necessary to use this factor for the calculation of air velocity where1.5meters downstream from the outlet cross-section of mixing chamber which defined as u1.5. Experimental and the CFD (Computational Fluid Dynamics) methods are applied to investigate the influence on performance of the air ejector. Four parameters are characterized:converging angle of entraining chamber θ; diameter of the mixing chamber Dm; the nozzle position (NXP) S and lenth of mixing chamber Lm.Up to241different models are established and meshed by Gambit2.3and then simulated and calculated by Fluent6.3with the turbulence model of RNG k-epsilon. Consequently,241different results containing flow rate of nozzle outlet cross-section Gp, entrainment flow rate Ge, flow rate of mixing chamber outlet cross-section Gm, air velocity of mixing chamber outlet cross-section uc are acquired. Based on these data, the response surfaces for u1.5, Lc and Ac which are used to investigate the interaction between Dm,θ, S and Lm to u.2.5and entrainment ratio have been established. The results indicate that the parameters Dmand θ have great influence on u1.5, Lc and Ac. It is also demonstrated that the interaction between Dm,θ and Lm is significant. However, parameter S gives a relative delicate influence on u1.5, Lc and Ac, and also the interaction with the other parameters is weak. In addition, to find out the mechanism of influence on u1.5, Lc and Ac, the pressure field and velocity field of every single factor of Dm,9, S and Lm have been investigated and compared as well. It indicates that high value of θ could create a relatively significant negative pressure zone in the mixing chamber, which requires a larger Dm to provide sufficient air input, as a consequence u1.5and entrainment ratio increase accordingly. Because of the negative pressure zone nearby nozzle outlet, the effective power of centrifugal fan and engine are increased both. The optimum value of θ is25.3°, when Dm equals to144mm, Lm equals to900mm, S equals to-60mm, u1.5could reach the maximum value. The maximum u1.5Lc and Ac which is gained by experiments using an ejecting pneumatic extinguisher, is32.6m/s,2.32m and0.060m2respectively, which exceeds the traditional pneumatic extinguisher8.31%,9.95%,62.2%. Meanwhile, the value of u1.5could keep adding up as Dm continues to increase, but the range of Dm has been limited by design and practical applicability of portable pneumatic extinguisher.For the MTE pneumatic ejecting extinguisher, Up to486different models are established and meshed by Gambit2.3and then simulated and calculated by Fluent6.3with the turbulence model of Spalart-Allmaras. Consequently,486different results containing flow rate of nozzle outlet cross-section Gp, entrainment flow rate Ge, flow rate of mixing chamber outlet cross-section Gm, air velocity of mixing chamber outlet cross-section uc are acquired. Based on these data, the response surfaces for u1.5, Lc and Ac which are used to investigate the interaction between Dm,9, S and Lm to u2.5and entrainment ratio have been established. The results indicate that the parameters Dmand9have great influence on u1.5, Lc and Ac. It is also demonstrated that the interaction between Dm,θ and Lm is significant. However, parameter S and9gives a delicate influence on M1.5, Lc and Ac. In addition, to find out the mechanism of influence on m1.5, Lc and Ac, the pressure field and velocity field of every single factor of Dm,θ, S and Lm have been investigated and compared as well. Because of the negative pressure zone nearby nozzle outlet, the effective power of centrifugal fan and engine are increased both. The optimum value of6is20°, when Dm equals to80mm, Lm equals to700mm,S equals to0, u1.5could reach the maximum value. The maximum u1.5, Lc and Ac which is gained by experiments using an ejecting pneumatic extinguisher, is42.7m/s,3.16m and0.091m2respectively. Meanwhile, the micro turbine pneumatic ejecting extinguisher has been designed and manufactured. Grassland fire extinguishing experiment has been carried out and it has been proved that the extinguishing effect of MTE pneumatic ejecting extinguisher is much better than portable pneumatic extinguisher.更多还原