【摘要】：已有研究表明采取恰當(dāng)?shù)娜~頂形狀對提高軸流風(fēng)機性能具有顯著影響。本文以某兩級動葉可調(diào)軸流一次風(fēng)機為對象,采用Fluent模擬了葉頂具有斜槽或階梯狀結(jié)構(gòu)等5種情形下的風(fēng)機性能,分析了其內(nèi)流特征、壓力分布和損失特征以確定性能優(yōu)良的葉型方案;在此基礎(chǔ)上,比較了兩級葉輪葉頂分別改型及同時改型時的風(fēng)機性能,分析了葉頂改型前后的內(nèi)流和泄漏損失特征。結(jié)果表明:5種葉頂形狀均可有效提高風(fēng)機性能,提升效果依次為逆流向斜槽、雙斜槽、上階梯葉頂和下階梯葉頂,而順流向斜槽僅在小流量下提升性能明顯;改進后的葉頂形狀均使泄漏流場更加復(fù)雜,且泄漏渦分布區(qū)域及強度明顯增大,葉頂間隙內(nèi)渦量值顯著提高,由此降低了葉頂間隙內(nèi)軸向速度和泄漏流量;其中,逆流向斜槽改善風(fēng)機性能最為突出,在設(shè)計流量下,全壓和效率分別提高4.68%和0.94%;考慮到當(dāng)前燃煤機組低排放改造后增大的煙風(fēng)阻力和風(fēng)量需求,逆流向斜槽葉頂是最佳葉型選擇。而不同級動葉葉頂改型同樣均可有效提高風(fēng)機性能,其總體提升效果依次為I級動葉葉頂改型、兩級葉頂同時改型和II級葉輪葉頂改型;雖然兩級葉頂同時改型后的全壓提升最大,但高效區(qū)較窄;葉頂改型后,葉頂間隙內(nèi)的內(nèi)流特征更加復(fù)雜,吸力面上的靜壓明顯降低,葉頂泄漏損失減小;考慮到機組變工況運行、超凈排放改造要求和葉頂改型成本,I級動葉實施葉頂改型是優(yōu)選方案。之后將不同葉型定常模擬所得流場作為初場,并引入大渦模擬和FW-H聲學(xué)模型獲得了不同葉頂形狀下風(fēng)機的噪聲源分布和氣動噪聲特征。結(jié)果表明:葉頂形狀改進后,葉頂泄漏渦的影響增強,造成葉頂區(qū)和葉片前緣噪聲顯著增大,為風(fēng)機內(nèi)主要噪聲源;風(fēng)機各區(qū)域的聲壓幅值均受顯著影響,且愈靠近噪聲源受影響愈突出;風(fēng)機內(nèi)噪聲主要以中低頻的旋轉(zhuǎn)噪聲為主,各區(qū)域噪聲均在基頻位置達到最大值,葉頂形狀改進后聲壓級隨頻率變化發(fā)生小幅度提高,頻譜形態(tài)發(fā)生明顯改變。
[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.
【學(xué)位授予單位】：華北電力大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TH432.1

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