导流罩长度对农用轴流风机性能的影响

通过三维激光扫描仪建立农用轴流风机几何模型，利用密闭风室试验测试数据验证数值模型的准确性，最后采用数值模拟研究了农用轴流风机导流罩长度变化对风机内外特性的影响。保持导流罩进口位置、圆角半径与扩散角不变，定义导流罩长度与叶顶轴向宽度的比值为K，K选取0.50、0.78、0.90、1.0、1.1、1.2、1.5、2.0，对7个不同进口静压工况点进行数值模拟。结果表明，K从0.50上升到1.0的过程中，风机风量和能效比提升明显；K取1.0~1.1时风机风量和能效比最高，相比K=0.78的原型风机提升约10%；K从1.1升至2.0的过程中，风量略有下降，能效比下降明显。利用Q准则对叶顶和外框区域的涡结构进行识别，发现随着K的增长，叶顶泄漏涡经历了分裂、衰减和再发展3个过程。K=1.0时能有效抑制叶顶泄漏涡的发展，最大程度降低叶顶涡的强度。导流罩的加长能明显减少外框涡的产生。

Influence of Length of Shroud on Performance of Agricultural Axial Fan

The geometric model of a 50-inch agricultural axial fan was established by a 3D laser scanner. The experimentally verified numerical model was used to study the influence of length of shroud of agricultural axial fan on the internal and external characteristics of fan. Keeping the inlet position of the shroud, the rounded corner radius and the diffusion angle were unchanged, and defining the ratio of length of shroud to axial width of tip as K. The value of K was chosen as 0.50, 0.78, 0.90, 1.0, 1.1, 1.2, 1.5 and 2.0. Totally seven different imported static pressure operating points were chosen for numerical simulation. The results showed that during the process of increasing the K from 0.50 to 1.0, the air volume and energy efficiency ratio of fan were obviously improved. When K was from 1.0 to 1.1, the fan air volume and energy efficiency ratio were the highest, which was about 10% higher than those of the prototype fan with K=0.78. When the K was from 1.1 to 2.0, the air volume was slightly decreased. The energy efficiency ratio was decreased significantly. Using the Q criterion to identify the vortex structure in the tip and outer frame regions, it was found that with the growth of K, the tip leakage vortex underwent three processes of division, attenuation and redevelopment. When K was 1.0 it can effectively inhibit the development of tip leakage vortex and minimize the strength of tip vortex. The lengthening of the shroud can significantly reduce the outer frame vortex.