叶顶改型对两级动叶可调轴流风机性能及噪声影响

发布时间：2019-06-28 17:16

【摘要】：已有研究表明采取恰当的叶顶形状对提高轴流风机性能具有显著影响。本文以某两级动叶可调轴流一次风机为对象,采用Fluent模拟了叶顶具有斜槽或阶梯状结构等5种情形下的风机性能,分析了其内流特征、压力分布和损失特征以确定性能优良的叶型方案;在此基础上,比较了两级叶轮叶顶分别改型及同时改型时的风机性能,分析了叶顶改型前后的内流和泄漏损失特征。结果表明:5种叶顶形状均可有效提高风机性能,提升效果依次为逆流向斜槽、双斜槽、上阶梯叶顶和下阶梯叶顶,而顺流向斜槽仅在小流量下提升性能明显;改进后的叶顶形状均使泄漏流场更加复杂,且泄漏涡分布区域及强度明显增大,叶顶间隙内涡量值显著提高,由此降低了叶顶间隙内轴向速度和泄漏流量;其中,逆流向斜槽改善风机性能最为突出,在设计流量下,全压和效率分别提高4.68%和0.94%;考虑到当前燃煤机组低排放改造后增大的烟风阻力和风量需求,逆流向斜槽叶顶是最佳叶型选择。而不同级动叶叶顶改型同样均可有效提高风机性能,其总体提升效果依次为I级动叶叶顶改型、两级叶顶同时改型和II级叶轮叶顶改型;虽然两级叶顶同时改型后的全压提升最大,但高效区较窄;叶顶改型后,叶顶间隙内的内流特征更加复杂,吸力面上的静压明显降低,叶顶泄漏损失减小;考虑到机组变工况运行、超净排放改造要求和叶顶改型成本,I级动叶实施叶顶改型是优选方案。之后将不同叶型定常模拟所得流场作为初场,并引入大涡模拟和FW-H声学模型获得了不同叶顶形状下风机的噪声源分布和气动噪声特征。结果表明:叶顶形状改进后,叶顶泄漏涡的影响增强,造成叶顶区和叶片前缘噪声显著增大,为风机内主要噪声源;风机各区域的声压幅值均受显著影响,且愈靠近噪声源受影响愈突出;风机内噪声主要以中低频的旋转噪声为主,各区域噪声均在基频位置达到最大值,叶顶形状改进后声压级随频率变化发生小幅度提高,频谱形态发生明显改变。
[Abstract]:It has been shown that proper blade top shape has a significant effect on the performance of axial flow fan. In this paper, taking a two-stage adjustable axial flow fan as the object, the performance of the fan with oblique groove or stepped structure is simulated by Fluent, and its internal flow characteristics, pressure distribution and loss characteristics are analyzed to determine the blade profile scheme with excellent performance. On this basis, the fan performance of the two stage impeller tip modification and simultaneous modification is compared, and the internal flow and leakage loss characteristics before and after the blade top modification are analyzed. The results show that the performance of the fan can be effectively improved by five kinds of blade top shapes, and the lifting effects are countercurrent oblique groove, double oblique groove, upper step blade top and lower step blade top, while the performance of the inclined groove along the flow direction is only obvious at small flow rate. The improved tip shape makes the leakage flow field more complex, and the distribution area and intensity of leakage vortex are obviously increased, and the vortex value in the tip clearance is significantly increased, which reduces the axial velocity and leakage flow rate in the tip clearance, among which the countercurrent oblique groove improves the fan performance the most, and the total pressure and efficiency increase by 4.68% and 0.94% respectively under the designed flow rate, and the total pressure and efficiency are increased by 4.68% and 0.94%, respectively, and the total pressure and efficiency are increased by 4.68% and 0.94%, respectively. Considering the increasing demand of smoke resistance and air volume after low emission transformation of coal-fired units, countercurrent oblique slot blade top is the best choice of blade shape. The performance of the fan can also be effectively improved by the top modification of different stages of the moving blade, and the overall improvement effect is as follows: the top of the moving blade is modified at the same time, the tip of the two stages is modified at the same time and the tip of the II impeller is modified at the same time, although the total pressure is the largest after the modification of the top of the blade, but the high efficiency area is narrower; after the modification of the tip, the internal flow characteristics in the clearance of the blade tip are more complex, the static pressure on the suction surface is obviously reduced, and the leakage loss of the blade top is reduced. Considering the operation of the unit under variable working conditions, the requirements of ultra-net emission transformation and the cost of blade top modification, the implementation of blade top modification of class I moving blade is the optimal scheme. Then the flow field obtained by steady simulation of different blade shapes is taken as the initial field, and the noise source distribution and pneumatic noise characteristics of fan with different blade top shapes are obtained by introducing large vortex simulation and FW-H acoustic model. The results show that after the shape of the blade top is improved, the influence of the tip leakage vortex is enhanced, resulting in a significant increase in the noise in the tip area and the front edge of the blade, which is the main noise source in the fan, and the sound pressure amplitude in each area of the fan is significantly affected, and the closer the noise source is, the more prominent the noise source is. The noise in the fan is mainly rotating noise in the middle and low frequency, and the noise in each region reaches the maximum at the fundamental frequency position. The sound pressure level increases slightly with the change of frequency, and the spectrum shape changes obviously after the shape of the blade top is improved.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TH432.1

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