马鞍屋盖表面分离泡流动形态研究

3-D flow characteristics of separation bubble around the saddle roof

利用粒子图像测速技术,通过风洞流场显示试验,给出了均匀流和格栅紊流两种工况下马鞍屋盖迎风高点和迎风低点处旋涡的截面形态特征以及时均、瞬时流线和涡量场分布,比较了两种工况下旋涡形态特征的异同,总结了来流在屋面上的速度分布规律。试验结果表明:当风向垂直于迎风前缘时,屋面迎风高点至迎风中点区域将出现典型的分离泡现象;而在迎风中点至低点区域,由于马鞍屋面为正向坡度,无法形成分离泡。均匀流场下分离泡再附长度近乎横跨整个屋盖;而湍流场中分离泡涡核离迎风前缘较近,且旋涡横截面积显著小于均匀流工况。结合风洞测压试验,分析了不同迎风高度处马鞍屋盖表面的脉动风压谱特性,明确了谱能量与旋涡运动或湍流尺度之间的演变关系。利用多个可视化平面的综合布置最终揭示出分离泡的三维形态特征,据此将马鞍屋盖划分为4个区域并提出合理的分区体型系数,为大跨马鞍屋盖抗风设计提供参考。

Through Particle Image Velocimetry （abbr. PIV）, flow visualization of separation bubble around saddle roofs was conducted in a wind tunnel. The vortex section morphology and time-average, instantaneous streamlines and vorticity field distribution were obtained under high and low windward point in uniform and grid-generated flow field. The characteristics of vortices were compared in different flow conditions. Velocity distribution rule of the visual plane on the roof surface was summarized. Results indicated that when the wind direction perpendicular to windward on the leading edge of the roof, the area between the high point windward and middle point windward will appear typical separation bubble phenomenon. Due to the positive slope of the saddle roof, there was no separation bubble at the low windward point. The reattached length is almost across the whole roof in uniform flow, while the vortex core was closer to the windward edge in turbulent flow and the vortex cross- sectional area significantly less than in uniform flow condition. With the result of the wind tunnel pressure measurement, the fluctuating wind pressure spectrum at different height of the windward were analyzed and established the spectrum evolution relationship between energy and vortex movement or turbulence scale. Three-dimensional morphological characteristics were obtained by analysis of the multiple visual planes comprehensive arrangement. The saddle roof was divided into four regions accordingly and put forward reasonable partition shape coefficient, providing reference to the large-span saddle roof wind resistance design.