下击暴流的风场特性以及其作用下高层建筑风荷载研究
发布时间：2018-11-21 13:05
【摘要】：随着全球气候变暖,以下击暴流等为代表的强对流天气逐渐增多,使得对其的研究成为目前国际风工程领域的热点问题之一。下击暴流是由雷暴天气中形成的强下沉气流冲击地面后,在地面加速扩展开的一种气流过程,由于下击暴流风剖面与大气边界层风剖面差异巨大,并且在距离地面很低处会产生强风荷载,往往会导致结构破坏。我国荷载规范只给出了大气边界层风荷载,对下击暴流的这类极端风并没有考虑在内。所以对下击暴流的研究就显得至关重要。本文基于冲击射流模型建立下击暴流三维模型,通过CFD数值方法对下击暴流的风场进行了定常数值模拟,对下击暴流的风场特征进行了重点分析。下击暴流径向风速在近地面附近达到最大值,之后随着高度增大而迅速减小,径向风速剖面与大气边界层剖面有着显著的差异。在下击暴流射流管下方距离喷射中心半径为1D的圆内都存在着正压,并且中心处压力系数接近1。不同射流速度对无量纲化的径向风速剖面影响不大,不同的射流高度H对无量纲化的径向风速剖面有着一定的影响。下击暴流的边界层的发展是呈非线性变化的。不同径向位置r处,下击暴流风剖面不同,建筑承受风荷载作用亦不同。利用CFD方法对不同径向位置处的高层建筑模型进行了风荷载特征分析。分别将模型置于距离下击暴流核心r=OD,r=1D,r=1.5D,r=2D四个不同位置,利用SSTk-co湍流模型进行定常数值模拟。不同径向位置处模型周围流场分析:在r=0D位置处,可以看到下沉的气流垂直撞击在高层建筑模型顶面,气流撞击顶面后向四周散开,并且在模型四个侧面周围气流形成一个封闭的汽缸。在r=1D,r=1.5D,r=2D位置处,在模型迎风面下部都存在一个气流驻点,在模型的侧面中上部,流动在侧面前端发生分离,在后端又发生了再附现象,而在模型下部没有发生再附现象。不同径向位置处模型表面风压系数分布分析:模型位于r=0D位置处时,模型各个表面均承受较大的压力,此位置处,建筑结构设计时应有着足够的抗压强度。在r=1D,r=1.5D,r=2D位置处,模型迎风面风压系数随着径向位置r的增大,峰值风压系数变小,并且在峰值风压系数附近区域风压系数变得不再饱满。在侧面与背面主要产生吸力,侧面上部,前端吸力大于后端。总体来看,径向位置对侧面、背面压力系数分布影响较小。
[Abstract]:With the global warming, the severe convective weather represented by the following storm currents is gradually increasing, which makes the research on it become one of the hot issues in the field of international wind engineering. The downburst flow is a kind of airflow process which is accelerated to expand on the ground after the strong sinking air flow formed by thunderstorm weather hits the ground. Because of the great difference between the downburst wind profile and the atmospheric boundary layer wind profile, Strong wind loads will occur at very low distances from the ground, which often lead to structural damage. The wind load of atmospheric boundary layer is only given in the load code of our country, and the extreme wind of downburst flow is not taken into account. Therefore, the study of downburst flow is very important. In this paper, based on impinging jet model, a three-dimensional model of downburst flow is established, and the wind field of downburst flow is simulated by CFD numerical method, and the wind field characteristics of downburst flow are analyzed emphatically. The radial wind speed of the downburst reaches its maximum near the ground and then decreases rapidly with the increase of height. The radial wind velocity profile is significantly different from the atmospheric boundary layer profile. The positive pressure exists in the circle where the radius of the jet center is 1 D below the jet tube, and the pressure coefficient is close to 1. Different jet velocities have little effect on the dimensionless radial wind profile, and different jet height H has a certain effect on the dimensionless radial wind velocity profile. The evolution of the boundary layer of the downburst flow is nonlinear. At different radial position r, the downburst wind profile is different, and the action of building bearing wind load is also different. The wind load characteristics of high-rise building models at different radial positions are analyzed by CFD method. The model was placed in four different positions at the core of storm flow at a distance. The SSTk-co turbulence model was used to carry out steady numerical simulation. Analysis of the flow field around the model at different radial positions: at rn0D position, it can be seen that the vertical impact of the sinking airflow is on the top surface of the model of the high-rise building, and the airflow impinges on the top surface and disperses around the top surface. A closed cylinder is formed around the four sides of the model. At the position of r ~ (1D) ~ r ~ (1) D ~ (1.5) D / r ~ (2 D), there is an airflow stop point in the lower part of the model's upwind surface. In the middle and upper side of the model, the flow is separated at the front end of the model, and the phenomenon of reattachment occurs at the back end. No reattachment occurred in the lower part of the model. Analysis of the distribution of wind pressure coefficient on the surface of the model at different radial positions: when the model is located at rn0D, each surface of the model is subjected to greater pressure. At this location, there should be sufficient compressive strength in the design of the building structure. The peak wind pressure coefficient decreases with the increase of radial position r, and becomes no longer full in the region near the peak wind pressure coefficient. Suction is mainly produced on the side and back, the upper side and the front end are larger than the back end. As a whole, the radial position has little effect on the distribution of the pressure coefficient on the side and back.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU973.213
本文编号：2347033
[Abstract]:With the global warming, the severe convective weather represented by the following storm currents is gradually increasing, which makes the research on it become one of the hot issues in the field of international wind engineering. The downburst flow is a kind of airflow process which is accelerated to expand on the ground after the strong sinking air flow formed by thunderstorm weather hits the ground. Because of the great difference between the downburst wind profile and the atmospheric boundary layer wind profile, Strong wind loads will occur at very low distances from the ground, which often lead to structural damage. The wind load of atmospheric boundary layer is only given in the load code of our country, and the extreme wind of downburst flow is not taken into account. Therefore, the study of downburst flow is very important. In this paper, based on impinging jet model, a three-dimensional model of downburst flow is established, and the wind field of downburst flow is simulated by CFD numerical method, and the wind field characteristics of downburst flow are analyzed emphatically. The radial wind speed of the downburst reaches its maximum near the ground and then decreases rapidly with the increase of height. The radial wind velocity profile is significantly different from the atmospheric boundary layer profile. The positive pressure exists in the circle where the radius of the jet center is 1 D below the jet tube, and the pressure coefficient is close to 1. Different jet velocities have little effect on the dimensionless radial wind profile, and different jet height H has a certain effect on the dimensionless radial wind velocity profile. The evolution of the boundary layer of the downburst flow is nonlinear. At different radial position r, the downburst wind profile is different, and the action of building bearing wind load is also different. The wind load characteristics of high-rise building models at different radial positions are analyzed by CFD method. The model was placed in four different positions at the core of storm flow at a distance. The SSTk-co turbulence model was used to carry out steady numerical simulation. Analysis of the flow field around the model at different radial positions: at rn0D position, it can be seen that the vertical impact of the sinking airflow is on the top surface of the model of the high-rise building, and the airflow impinges on the top surface and disperses around the top surface. A closed cylinder is formed around the four sides of the model. At the position of r ~ (1D) ~ r ~ (1) D ~ (1.5) D / r ~ (2 D), there is an airflow stop point in the lower part of the model's upwind surface. In the middle and upper side of the model, the flow is separated at the front end of the model, and the phenomenon of reattachment occurs at the back end. No reattachment occurred in the lower part of the model. Analysis of the distribution of wind pressure coefficient on the surface of the model at different radial positions: when the model is located at rn0D, each surface of the model is subjected to greater pressure. At this location, there should be sufficient compressive strength in the design of the building structure. The peak wind pressure coefficient decreases with the increase of radial position r, and becomes no longer full in the region near the peak wind pressure coefficient. Suction is mainly produced on the side and back, the upper side and the front end are larger than the back end. As a whole, the radial position has little effect on the distribution of the pressure coefficient on the side and back.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU973.213
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