轴流式通风机数值模拟及气动噪声分析

发布时间：2018-04-17 07:17

本文选题：轴流式通风机 + 内部流场　；参考：《东北石油大学》2017年硕士论文

【摘要】：风机主要是用于输送气体的叶轮机械,被广泛应用于国民经济的各个生产部门,尤其是在矿山、冶金、石油、化工、航天航空、船舶机械、能源以及车辆工程等领域。由于石油化工涉及的气体往往是有毒、易燃、易爆的介质,对通风机的要求就更加苛刻,必须在结构、操作条件和安全防范措施方面保障通风机运行安全可靠。因此改善风机内部流场分布、提高风机P-Q性能以及降低风机气动噪声逐渐受到广大学者的重视。本文的研究对象为轴流式通风机,采用商用计算流体软件FLUENT14.5对该轴流式通风机的内部流场进行数值计算,分析不同叶轮转速下风机内部流场分布变化规律,以及风机性能曲线变化规律;采用相同的数值计算方法分析存在分流叶片时风机内流场分布,并分析不同分流叶片尺寸对轴流式通风机内部流场分布影响。轴流式通风机在运行过程中往往伴随着强烈的噪声,其主要有两部分组成:一是由于风机叶轮旋转时叶片产生周期噪声;二是由于空气流过叶轮流道时,出现附面层分离和尾迹流现象而产生的空气涡流扰动噪声。本文采用Lighthill声比拟法,并结合LES和FW-H混合模型,对该轴流式通风机进行三维非定常流动噪声数值求解,得出叶轮转速对风机噪声频谱分布及总声压级值的影响;并分析分流叶片对风机噪声频谱分布及总声压级值的影响。为今后轴流式通风机结构设计以及风机降噪处理提供理论依据。通过数值计算表明,风机叶轮的压力面静压远高于吸力面静压,压力面静压为正压,而吸力面静压为负压,这是叶轮做功的标志;气流经轴流式通风机叶轮做功,其速度沿轴向方向逐渐增大,动能也随之提高;而静压沿轴向方向逐渐减小,静压能转化为气体动能。另外,由于叶轮尾部边界流动受到横向压力作用,使气流产生平行于边界的偏移,从而在风机叶轮尾部产生二次涡流。当存在分流叶片时,气体流经分流流道,静压能转为气体动能,气体流速增大而静压降低;随着分流叶片尺寸变窄,与叶轮之间的流道变宽,气体流速降低而静压再次升高;另外,分流叶片可使风机内静压分布更加均匀,减少压力脉动,从而有效抑制了气体与叶轮吸力面的流动分离现象;也可削弱叶轮尾部边界流动受横向压力作用而引起的二次流,大大改善叶轮末端尾流扰动。风机入口处的总声压级值较低,其主要是叶轮旋转引起叶片附近气流扰动的旋转噪声;而风机出口处总声压级值较高,其处于叶轮尾迹流和分离脱涡流动区域,涡流扰动强烈,在旋转噪声的基础上叠加涡流噪声。另外,分流叶片可降低气体在风机流道内的流阻,使叶轮吸力面低能区静压上升,减少脱涡流的产生并冲刷叶轮末端二次尾流,从而降低涡流噪声;若分流叶片尺寸过短,叶轮吸力面附近静压较无分流叶片时低,增强风机流道内的分离损失,叶轮吸力面脱涡严重,涡流噪声增强。
[Abstract]:Fan is mainly used for conveying gas impeller machinery, which is widely used in various production sectors of the national economy, especially in mining, metallurgy, petroleum, chemical, aerospace, marine machinery, energy and vehicle engineering and other fields.Since the gases involved in petrochemical industry are often toxic, flammable and explosive medium, the requirements for ventilators are more stringent. It is necessary to ensure the safe and reliable operation of ventilators in terms of structure, operating conditions and safety precautions.Therefore, to improve the flow field distribution, to improve the performance of the fan P-Q and to reduce the fan aerodynamic noise has been paid more and more attention by many scholars.The research object of this paper is axial flow fan. The internal flow field of axial flow fan is numerically calculated by commercial computational fluid software FLUENT14.5, and the variation law of flow field is analyzed under different impeller speed.With the same numerical calculation method, the distribution of flow field in the fan with shunt blade is analyzed, and the influence of different shunt blade size on the flow field distribution in axial fan is analyzed.The axial flow fan is usually accompanied by strong noise during operation, which mainly consists of two parts: one is that the blade produces periodic noise when the fan impeller rotates, the other is because the air flows through the impeller runner,Eddy current disturbance noise caused by boundary layer separation and wake flow.In this paper, by using Lighthill sound analogy method and LES and FW-H mixed model, the three-dimensional unsteady flow noise of the axial flow fan is numerically solved, and the influence of impeller speed on the noise spectrum distribution and the total sound pressure level of the fan is obtained.The influence of shunt blade on noise spectrum distribution and total sound pressure level of fan is analyzed.It provides the theoretical basis for the structure design of axial flow fan and the noise reduction of fan in the future.The numerical calculation shows that the static pressure of the fan impeller is much higher than that of the suction surface, the static pressure on the pressure surface is positive pressure, and the static pressure on the suction surface is negative pressure, which is the sign of the work done by the impeller.The velocity increases gradually along the axial direction and the kinetic energy increases, while the static pressure decreases along the axial direction, and the static pressure energy is converted into the kinetic energy of the gas.In addition, due to the lateral pressure acting on the tail boundary flow of the impeller, the flow is offset parallel to the boundary, thus the secondary eddy current is produced in the tail of the fan impeller.When there is a shunt blade, the static pressure energy is converted into gas kinetic energy, the gas velocity increases and the static pressure decreases, and with the size of the shunt blade becoming narrower, the passage between the shunt blade and the impeller becomes wider, and the gas velocity decreases and the static pressure increases again.In addition, the shunt blade can make the static pressure distribution in the fan more uniform and reduce the pressure pulsation, thus effectively restrain the flow separation phenomenon between the gas and the suction surface of the impeller.The secondary flow caused by transverse pressure on the tail boundary flow of impeller can also be weakened, and the wake disturbance at the end of impeller can be greatly improved.The total sound pressure level at the inlet of the fan is low, which is mainly the rotating noise caused by the impeller rotation, while the total sound pressure level at the outlet of the fan is higher, which is located in the impeller wake flow and the separation of the eddy current, and the eddy current disturbance is strong.The swirl noise is superimposed on the basis of rotating noise.In addition, the shunt blade can reduce the flow resistance of the gas in the fan channel, increase the static pressure in the low energy area of the suction surface of the impeller, reduce the generation of deswirl and wash the secondary wake at the end of the impeller, thereby reducing the eddy current noise; if the size of the shunt blade is too short,The static pressure near the suction surface of the impeller is lower than that of the blade without shunt, which enhances the separation loss in the fan passage, and the impeller suction surface devortex seriously, and the eddy current noise is enhanced.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH432.1

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