大跨屋盖表面旋涡的PIV试验研究

PIV EXPERIMENTAL INVESTIGATION OF VORTICES ON LARGE-SPAN ROOFS

该文通过风洞流场显示试验,观察了大跨平屋盖和马鞍屋盖表面的分离泡和锥形涡现象,给出了不同风向、不同屋盖表面的旋涡流线和涡量场分布;分析了风向角、屋盖曲率对于旋涡形态的影响。试验结果表明,当风向垂直于平屋盖迎风前缘时,屋盖表面将形成典型的分离泡现象,且分离泡的涡核位置恰好对应了涡量场的负向峰值。在斜向风作用下,平屋盖和以高点作为迎风点的马鞍屋盖表面将出现锥形涡。观察旋涡的平均流线和涡量场分布图,发现当来流沿两种屋盖对角线时,锥形涡截面形状接近圆形;当来流偏离屋盖对角线时,在靠近来流的一侧,锥形涡截面形状接近椭圆形;流场内负向涡量分布于壁面上,峰值集中在迎风前缘附近和旋涡周围。在相同的风向角下,曲率较大的马鞍表面锥形涡涡轴与屋盖迎风前缘所成角度较大,曲率较小的马鞍表面锥形涡涡轴与迎风前缘所成角度较小。此外,旋涡的瞬时流线图表明,锥形涡是一种瞬时变化的流体现象,其形态和位置在每个瞬时都不相同。

Through Particle Image Velocimetry(PIV), flow visualization of separation bubble and conical vortices on large-span flat and saddle roofs was conducted in a wind tunnel. The streamline and vorticity field of visual planes on large-span roofs were derived by PIV. The influence of wind direction and roof curvature on the appearance of conical vortices was discussed. The results indicate that separated bubble occurs when the flow is normal to the leading edge of the flat roof. The location of the vortex core is corresponding to the negative peak vorticity. For cornering flow, conical vortices are observed near the leading edge of the flat roof and the saddle roofs whose high points are windward. When the wind direction changes from along the diagonal to deviating from the diagonal of the roofs, the conical vortex close to the approaching flow changes to be more oblong shaped. The negative vorticity is concentrated on the roof surface, while the peak is near the leading edge and around the vortices. At the same wind direction, a greater roof curvature leads to a larger angle between the vortex axis of conical vortices and the leading edge of the saddle roof. The instantaneous streamline of the visual planes illustrates that conical vortices are resizing and swaying constantly, which reveals its intermittent characteristic.