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《太阳能学报》2017,(11)
为避免由经验性地选择湍流风谱模型导致特定风电场风速分布规律描述不准确的问题,基于Kaimal、Von Karman、SMOOTH和NWTCUP湍流风谱模型模拟在不同地表粗糙度和湍流强度条件下所建立风场的风速分布规律,通过计盒维数分形方法计算不同风速速度曲线的分形维数,并与某风电场测风塔实测风速数据的分形维数进行比较。结果表明:风速曲线的分形维数均约为1.5,证明风速时域分布具有自相似特征。由于NWTCUP湍流风谱模型基于所选风电场的实测风速数据建立,因此NWTCUP模型在50 m高度和80 m高度处的风速分形维数与实测数据最为接近,表明分形维数可作为选择湍流风谱模型的一个重要定量参数。 相似文献
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为探究风力机叶片动态特性与分形维数之间的关系,基于湍流风谱模型Von Karman和NWTCUP生成2种风场,通过多体动力学软件FAST仿真出不同风速条件下的风力机叶片挥舞和摆振时域动态响应,采用计盒维数法求解其分形维数。用发电机输出功率验证分形维数描述风力机叶片动态特性的可行性。结果表明:挥舞时域动态响应的分形维数随风速的增大逐渐减小,而摆振则相反,当达到额定功率时挥舞和摆振的分形维数变化都较小;相同风速下不同湍流风谱模型的功率虽几乎相同,但其对应的分形维数却不同,表明不同的湍流风谱模型有其特定的分形维数。 相似文献
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《内燃机学报》2016,(3)
气门间隙异常是柴油机常见机械故障之一,对其进行准确的诊断对提高柴油机的使用寿命具有积极的作用.针对柴油机气门间隙异常的问题,在某直列6缸柴油机上模拟了不同气门故障,提出了基于双谱估计、图像处理以及分形理论相结合的故障诊断方法.该方法首先利用双谱估计对非线性、非高斯信号的敏感性质,分析了不同故障状态下振动信号中非高斯成分及二次相位耦合特性,然后通过图像处理技术将双谱图表示为以像素位置及对应颜色强度构成的三维空间曲面,最后利用分形理论提取该曲面的分形盒维数作为故障特征.结果表明:不同状态下柴油机振动信号的双谱及其图像分形维数明显可分,正常状态下的双谱峰值分布最为复杂、分形维数最大,故障状态下的分形维数分别处在不同的范围.因此,以振动信号的分形维数作为特征值可实现柴油机气门故障诊断. 相似文献
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对一台引进的300 MW机组W火焰锅炉炉内煤粉气流的着火特性进行了研究,测试了不同二次风挡板开度及煤粉浓缩器上乏气挡板开度下燃烧器区域烟气温度分布.结果表明二次风挡板和乏气挡板的开度在不同程度上影响到炉内着火特性;虽然乏气挡板开度能影响煤粉浓缩器浓、淡两侧的气相分配,但其对煤粉气流着火的影响较二次风挡板开度弱的多,究其原因在于燃烧器喷口采用一、二次风喷口相间布置,二次风离开喷口后极易与浓煤粉气流混合,这直接影响到煤粉气流的着火. 相似文献
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An experimental study of a cross-flow type plate heat exchanger for dehumidification/cooling 总被引:1,自引:0,他引:1
The thermal and dehumidification behaviour of a standard cross-flow type plate heat exchanger, intended for use as a dehumidifier/cooler, has been investigated both experimentally and numerically. Three sets of experiments have been carried out where air is blown into the primary and secondary sides of the exchanger, while water and liquid desiccant were being sprayed in a counter flow arrangement. The first set represents the indirect evaporative cooling of the primary stream by the secondary air stream. The second set is with liquid desiccant only and no indirect evaporative cooling. In the third set of experiments the primary air stream is indirectly evaporatively cooled by the secondary air stream and dehumidified by the liquid desiccant sprayed into the primary side of the exchanger. The above experiments indicate that the heat exchanger performs well when used with liquid desiccant. Furthermore, for an exchanger angle of 45°, there is an optimum value of air mass flow rate at which the effectiveness and dehumidification efficiency of the plate heat exchanger are maxima. To investigate the effect of the ambient air conditions on the PHE performance, further experiments were carried out using a heater element and a humidifier. The results show that under laboratory conditions the exchanger effectiveness and dehumidification efficiency increase with increasing primary air inlet temperature and humidity ratio. The experimental results were used to validate a computer model developed for the cross-flow type plate heat exchanger/dehumidifier. Comparison indicates that the numerical results are in good agreement with the experiments. 相似文献
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The purpose of this study is to determine how different design parameters in an idealised small-scale combustor affect the emission of particulates in the flue gas and to provide insight that can be used for design optimisation. The design parameters are the primary air factor, the total air factor and the magnitude of swirling flow in the combustion chamber. Particles from the reactor were collected from two different sampling lines, one located in the combustion zone, just above the fuel bed, and the other in the flue stack after the reactor. The measurements show that this burner gives very low emissions of particulates and CO in the flue gas. Furthermore, the concentration of particles in the flue gas is uncoupled to the concentration of particles immediately above the fuel bed, probably as a result of a well-designed secondary air supply. The variable that had the strongest effect on the total particulate emission from the combustor was the total air factor. In order to understand the qualitative differences in the flow nature between different operating conditions, CFD simulations of the flow field were also performed. 相似文献
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600 MW前后墙布置燃烧器锅炉的NOx排放特性及其影响因素的分析 总被引:2,自引:0,他引:2
以2台600 MW超临界机组前后墙布置燃烧器的锅炉为研究对象,采用现场燃烧调整试验方法,进行了氧量、燃烧结构参数(包括一次风速、中心风量、二、三次风风量和二次风旋流强度等)、磨煤机运行组合方式、燃尽风量、煤质变化等运行条件对锅炉NOx排放特性影响的试验研究;采用统计分析方法对各种影响因素进行了定量分析和比较.结果表明:锅炉的运行氧量、磨煤机组合投运方式变化、燃尽风量是影响锅炉NOx排放浓度的主要因素,煤质的变化也不可忽视,经比较,燃烧器结构参数变化的影响较小;通过对主要因素的控制,可以显著降低锅炉NOx排放浓度,同时实现高锅炉效率. 相似文献
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炉膛(CFS系统)燃烧过程的数值模拟及工程应用 总被引:6,自引:0,他引:6
本文以某厂四角燃煤锅炉为例,进行一、二次风同心正反切时炉内冷、热态试验研究,并进行数值模拟与之对照。试验和数值模拟结果均表明:当一、二次风气流以一定角度交叉送入炉膛时,合理调节一、二次风气流配风角度,采用合适的一、二次风动量矩的比值,能够改善炉内空气动力结构,减少煤粉气流刷墙贴壁,有利于防止燃烧器区结渣。 相似文献
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This paper describes the performance analysis of a cross-flow type plate heat exchanger for use as a liquid desiccant absorber (dehumidifier) and indirect evaporative cooler. The proposed absorber can be described as a direct contact, cross-flow, heat and mass exchanger, with the flow passages separated from each other by thin plastic plates. One air stream (primary air) is sprayed by liquid desiccant solution, while the other stream (secondary air) is evaporatively cooled by a water spray. Each thin plate, besides separating the water/air passage from the solution/air passage, also provides the contact area for heat and mass transfer between the fluids flowing in each passage. A parametric study for the primary air stream at 33°C, 0.0171 kg/kg humidity ratio and secondary air stream at 27°C and 0.010 kg/kg humidity ratio using calcium chloride solution was performed in this study. The results showed a strong dependence on the heat and mass transfer area, solution concentration and ratio of secondary to primary air mass flow rates. However, negligible differences were found between the performance of a counter flow and a parallel flow arrangement. The results demonstrate that the proposed absorber will not offset both the latent and sensible load of the primary air and, therefore, an auxiliary cooler or more dehumidification/indirect evaporative cooling stages will generally be required to meet the sensible and latent load in a typical comfort application. 相似文献