共查询到19条相似文献,搜索用时 375 毫秒
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正一、影响因素涡街流量计的工作原理是在流体中设置漩涡发生体,从而发生体两侧交替产生有规则的漩涡,漩涡列在漩涡发生体下游非对称地排列,产生一定的频率,通过公式f=St×v/(1-1.27d/D)×d(式中:St——斯特劳哈尔数,为无量纲数,与漩涡发生体及雷诺数有关;v——流速;d——发生体迎面宽度;D——公称通径)即可得出流速。一般来说,涡街流量计输出信号(频率)不受流体 相似文献
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针对高压降类调节阀涡激振动现象,设计多通道迷宫盘片和多级套筒组合高压降调节阀。基于计算流体动力学(CFD)和流固耦合模态分析法,计算调节阀内部瞬态流场及结构模态,得到其三种典型开度的流体流动情况,升力系数时域和频域特性曲线,以及模态频率和模态振型。分析结果表明:4s时刻,随调节阀开度减小,流体最大流速相应减小,第四级套筒外部流道区域的大涡逐渐形成小涡。调节阀全开时流体升力系数波动比70%和40%开度时更为剧烈,一阶模态频率、二阶模态频率均随开度的增大而增大。调节阀模态频率没有落在漩涡脱落主频率范围内,调节阀不会发生涡激振动锁定现象。 相似文献
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一、涡街流量计的工作原理及测量方法涡街流量计的工作原理是在流体中设置漩涡发生体,从而发生体两侧交替地产生有规则的漩涡,漩涡列在漩涡发生体下游非对称地排列,发生一定的频率,通过以下公式即可得出流速:f=St×v/(1-1.27d/D)×d式中:St——斯特劳哈尔数,为无量纲数,与漩涡发生体及雷诺数有关;v——流速;d——发生体迎面宽度;D——公称通径。临界流文丘里喷嘴由一个光滑的圆形入口部分收敛到最低咽喉区,气体通过喷嘴时,其速度增加,它的密度减小。在喉部,最小面积达到所需的音速 相似文献
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光纤式有源流量传感器是近年来发展起来的一种基于光纤传感技术、流量检测技术的新型流量传感器.目前,主要将金属薄膜的光热转换效应或电阻的热效应与光纤及光纤光栅的温度、应力特性(在流体环境下光的强度、频率、波长及相位等受温度、应力调制的特性)相结合并制得一类新型的光纤有源流量传感器,包括光纤光栅点式及光纤散射(布里渊、瑞利)分布式有源流量传感器.通过文献综述的方式来介绍有源光纤式流量传感器的工作原理、种类及其研究进展,旨在为今后研究提供方法. 相似文献
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<正>一、简介涡街流量计的测量原理如图1所示。在流体管道中插入一定形状的漩涡发生体(阻流体),当流体绕过发生体后,在发生体两侧会交替产生规则的漩涡,这种漩涡称卡门涡街。 相似文献
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气举用振荡脉冲射流破碎器的研究 总被引:3,自引:1,他引:2
本文着重研究了气举用振荡脉冲射流破碎器在淹没条件下的动态特性、冲蚀特性和现场试验情况。实验表明在淹没条件下振荡脉冲射流不仅具有强烈的动态脉动冲击特性,而且具有波动的径向流动(附壁流动)。在相同条件下振荡压力能破碎连续射流所不能破坏的土岩,而且能产生波动上举力;波动的径向流动使作用在破碎的土岩颗粒上的升力增大,使作用在土岩颗粒上的上举力大于压持力,导致土岩颗粒易于流动。在气举上使用脉冲射流喷嘴,其轴吸浓度稳定,提取的固液混合液浓度比采用连续射流喷嘴时的大。 相似文献
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孔腔流动发声是气动声学研究领域重要的课题,基于大涡模拟和Lighthill声类比方法,探讨了气体在孔腔流动的流激噪声的发声特性。模拟结果表明,孔腔边界层出口剪切涡、边棱处涡街和腔体内反馈涡的运动诱导了孔腔发声,具有明显的偶极子特性,在高频段腔体内激发了声学驻波模态。通过模拟与实验对比分析了不同流量下噪声量级以及频谱分布规律,研究结果表明:24 kHz以下的声频谱会表现出波峰小范围迁移;24 kHz以上频率对应的声压级随流量增大而增大;腔体长度和特征频率近似满足Strouher公式,即声频特征频率随腔体长度的增大而减小。上述研究结果为下一步设计在线监测安全阀泄漏的报警超声波发声器提供了理论依据。 相似文献
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倒角和切角措施对方柱的气动力及流场影响很大,常作为方柱流动控制的手段,采用大涡模拟方法,以雷诺数22000的方柱为研究对象,考虑了角部措施(角部变化率10%)的影响,对均匀流场下标准方柱、倒角和切角方柱周围流场及气动性能进行了模拟研究。通过将标准方柱大涡模拟结果与相关文献的试验和数值模拟结果对比,验证了该方法及参数取值的有效性;研究分析了倒角和切角措施对方柱风压分布和气动力的影响,并着重从时均流场和瞬态流场角度分析了角部处理措施对方柱气动性能的影响机理。结果表明,倒角和切角措施对方柱表面风压分布和气动力均有一定影响,其中对方柱表面流动分离区的风压系数影响更为显著。采用角部处理措施后,方柱前缘角区的流动分离受到影响,分离剪切层扩散角更小,侧面的分离涡更贴近壁面,从而在方柱侧面形成再附,尾流变窄,旋涡脱落频率成分更为复杂,使得方柱的平均阻力系数更小,气动力脉动强度更弱,旋涡脱落频率更高、强度更弱。 相似文献
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为准确捕捉小开度流动的瞬态湍流特性,充分了解流场结构,采用滑移网格技术以及基于Vreman亚格子模型的全局动态大涡模拟方法,不仅得到混流式水轮机全流道内速度、压力以及涡量的分布,同时捕捉到了活动导叶周围独特的流动形式和叶道涡的时空演化。计算结果表明:当高转速、小开度工况时,流道内流体的圆周速度占有绝对优势,加强了导叶后尾迹涡的相互影响,致使流道中发生更为剧烈和复杂的漩涡、脱流等各种水力不稳定现象。从蜗壳到转轮室的压力脉动均以低频为主,主要的频率能量成分基本相同,说明小开度低频异常振动与压力波的传递有关。叶道涡是致使叶片疲劳破坏的主要因素。 相似文献
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Y. Zimmels 《Particulate Science and Technology》1994,12(1):21-44
The stability of an assembly of particles which are suspended in a flow field of a gas, under the action of force fields, is considered. It is shown that the stability of the particle dispersion depends on the composite energy density due to the flow and the force fields. The stability can be maintained by balancing the change occurring in the flow and force fields, so that the total energy density after the change remains fixed. This capability is well established in Magnetically Stabilized Fluidized Beds (MSFBs), where the magnetic field can be used to lower the energy of the system against the rise in the kinetic energy of the fluidizing gas. A general criterion for stability is formulated in terms of the balance between energy densities that can be assigned to the dispersion as a composite entity. The sedimentation behavior of particles fluidized by gas discloses the factors that affect the intensity of instability of these systems. Simulation of batch sedimentation of concentrated, i.e. low voidage, polydisperse particle mixtures shows that the evolution of voidage disturbances is enhanced at higher particle concentrations and narrower size distributions. Under these conditions, relaxation time of the system becomes too high so that the evolution of the disturbance cannot be suppressed. This behaviour is the result of fluid particle interaction and the high sensitivity of the system to relatively small voidage perturbation. The application of polarization fields can eliminate this high sensitivity and render the system more stable. The extra stability is achieved by formation of ordered, pearl chain structures of the polarized particles. These structures render the system higher permeability levels to the flow of gas, thus allowing higher velocities at the same pressure drop. Alternatively, the formation of pearl chains changes the fluid particles interactions, decreasing the fluid drag and increasing the sedimentation velocity of the particles. 相似文献
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《Composites》1987,18(4):309-316
A system of thin, light-conducting fibres, integrated into a composite structure during its manufacturing process, can serve as a reliable, automatic and remote working long-term monitoring device for structural damage. Fractures, cracks or delaminations in a structure area can destroy the optical fibres installed there and thus interrupt the light flow. Various examples of applications in gfrp aircraft components are described. The outline of a complete fibre optic nervous system (fons) for large Airbus cfrp components shows how fibre optic damage detection can contribute to future aircraft maintenance and inspection philosophies. Following the example of other aircraft systems including engines and computers, the structure can also be included in the permanent and automatic working central fault detection system (cfds). 相似文献
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L. J. Blum S. M. Gautier P. R. Coulet 《Journal of materials science. Materials in medicine》1991,2(4):202-204
A fibre optic biosensor involving immobilized bioluminescence enzymes associated with a glass fibre bundle has been designed. The firefly luciferase fromPhotinus pyralis, as well as the bacterial luciferase-oxidoreductase system from eitherVibrio fischeri orVibrio harveyi, have been immobilized on preactivated polyamide membranes. First, the validity of the approach is demonstrated by performing the microdetermination of adenosine triphosphate (ATP) and sodium dehydrogenase (NADH) in a batch system. The detection limits are equal to 0.1nm for ATP and 0.3nm for NADH. With the NADH-based system, the extension of the biosensor potential to other analytes (ethanol, sorbitol and oxaloacetate) has been achieved using suitable dehydrogenases co-immobilized with the bacterial system. Second, the fibre optic biosensor is associated with a specially designed flow cell for the continuous-flow bioluminescent assay of NADH over the range 2 pmol-1 nmol with an r.s.d. of 3.4% at 0.1 nmol. Finally, a multifunction biosensor for the determination of either ATP or NADH using a single bioluminescence-based fibre optic probe is described. This was made possible by co-immobilizing the firefly luciferase with the bacterial system on the same preactivated polyamide membrane. 相似文献