叶轮弧盘及锥盘型线对高比转速离心通风机性能的影响

Effect of arc and taper plate impellers on performance of high specific speed centrifugal fan

为改善离心通风机的气动性能,该文以一高比转速离心通风机为研究对象,结合试验和全通道数值模拟研究了锥盘及4种不同弧盘叶轮对离心通风机性能的影响,通过对非定常流场及压力脉动信号的分析得到了前盘型线对高比转速离心通风机性能的影响机理。研究结果表明,随着比转速的增大,叶轮前盘型线对离心通风机效率的影响程度增大,比转速为73和120时,弧盘叶轮较锥盘叶轮效率分别提高5%和14.5%。高比转速离心通风机锥盘叶轮在靠近前盘处的流动分离现象过早,并一直延伸至叶轮出口,在无叶扩压器区域沿轴向出现环流,严重阻碍流体流入蜗壳。将锥盘改为弧盘后,叶片负荷和出口气流角增大,流动分离损失降低,出口压力脉动幅值降低。对前盘弧线进一步优化后,弧盘叶轮边界层损失和压力脉动进一步减小,在设计工况(38 205.63 m^3/h)下效率较原弧盘叶轮提升了1%。该研究成果为高比转速离心通风机叶轮的设计以及内部流动特性的研究提供了参考。

Centrifugal fans are widely used in agriculture, energy, chemical, smelting, papermaking, and environmental protection industries. With the development of our society and the widespread use of centrifugal fans, the high demands on performance of centrifugal fans are expected. Raising the efficiency of centrifugal fan is extremely important for energy saving and emission reduction, which is conducive to promoting the construction of a resource-saving and environment-friendly society. In practical engineering applications, such as exhaust fans, the specific speed becomes higher with the higher requirement of mass flow. Due to traditional experiences in design, high specific speed (100 - 200) fans are mostly designed as axial flow type. If centrifugal fans are replaced with axial fans, it does not conform to the concept of energy conservation and emission reduction in consideration of site constraints, on-site installation and cost. Therefore, it is more economical and feasible to replace the centrifugal impeller without changing the original volute. The high specific speed centrifugal impeller is characterized as large flow, low pressure rise and small impeller diameter. With the much effort by scholars, the high specific speed centrifugal impeller has been applied in the fields of pump and compressor in recent years. The design of high specific speed can make the impeller operate in the high-efficient area. Meanwhile, it has the advantages of reducing the size of impeller and cost. The centrifugal fans are mechanically different from pumps and compressors, and the flow field is extremely complex. The design methodology of high specific speed centrifugal compressor may not be suitable for centrifugal fan. The development of high specific speed centrifugal fan impeller is still in active demand. To our best knowledge, little effort is made on the research of high specific speed centrifugal fan. Therefore, in this paper, we used a high specific speed centrifugal fan with a specific speed of 120 as the research object. Compared with the original front taper plate of impeller, four kinds of impeller with different front arc plates were designed by reducing the outlet width. Through experimental verification and numerical simulation, the effects of different front plate impellers on the high specific speed centrifugal fan performance were analyzed experimentally and numerically. The mechanisms of efficiency enhancement were also studied. For the full-annulus three-dimensional simulation of the high specific speed centrifugal fan, the standard κ-ε turbulence model was used. The calculation domain contained inlet pipe, impeller, volute and outlet pipe. All domains were equipped with hexahedral structured grids. The results of numerical simulation were in agreement with the experiment, which confirmed that the numerical simulation model and the calculation methods could be used to predict the internal-flow in the high specific speed centrifugal fan. The results showed that the maximum efficiency point of the high specific speed impeller was offset to large flow condition. With the enhancement of the specific speed, the influence of impeller shrouds was increased. When the specific speed was 73 and 120, the efficiency of front arc plate impeller was increased by 5% and 14.5%, respectively compared with front taper plate impeller. The pressure gradient of high specific speed centrifugal fan front taper plate impeller near the shroud is irregular. At the same time, the flow separation occurs prematurely and extends to flow channels, these produced a large number of passage vortex in the flow channel. As the flow separation further extended to exports, the fluid circulations seriously prevented the fluid from flowing into the volute. The optimized front arc plate impeller exit flow angles were increased. Moreover, the amplitude of pressure fluctuation at impeller outlet and turbulence kinetic energy was reduced. The better front arc plate impeller can further reduce boundary layer loss and improve operation stability, so that the efficiency was improved by 1% under the design condition. The conclusion in this paper had reference value for the design and study of internal flow in the impeller of centrifugal fan with high specific speed.