小流量工况下离心风机蜗壳内部的三维流动测量分析

Measurement and Analysis of Three-Dimensional Flow in a Centrifugal Fan Volute at Low Flow Rate

利用五孔探针对小流量工况下离心通风机大宽度矩形截面蜗壳内部的三维流动进行了详细的测量 ,给出了蜗壳螺旋通道部分的 3～ 8个横截面内比较清晰的时均速度、静压和总压的分布图形 .结果表明 ,在小流量工况下 ,蜗壳内部的二次旋涡在蜗舌处就开始形成 ,在一个横截面内 ,由开始有 1个涡发展成 2个、甚至 3个涡 ;速度沿径向的分布与动量矩守恒规律有比较明显的差别 ,特别是蜗舌附近区域的速度和压力分布与通常的分析有很大不同 ;蜗壳内的损失可初步归纳为 4种 :二次流损失、内泄漏损失、冲击损失和磨擦损失 ;在小流量工况下 ,二次流损失和内泄漏损失相对最为严重 .

The 3-D flow in a centrifugal fan volute, which has a big volute width and a rectangular cross section, has been measured by means of a five-hole probe at 1600 r/min and a low flowrate. The time-average velocity, static and total pressure distributions in 3-8 cross sections along the through-flow direction of the volute are presented. These results show some peculiar flow phenomena. Under the condition of low flowrate, the swirling flow has been formed in the cross section at the volute tongue, and along the through-flow direction, the number of swirls in a cross section is increased progressively from one to two, even to three. In the cross sections of volute, the velocity distributions along radial direction are different from the law of conservation of momentum. Near the area of volute tongue, the velocity and pressure distributions are different obviously from the original understanding. The types of main hydraulic losses in this kind of fan volute at low flowrate may be preliminarily suggested as swirling flow loss, inner leakage loss, shock loss and friction loss. Under the condition of low flowrate, the losses due to swirling flow and inner leakage are usually higher than others.