超大型冷却塔施工全过程风荷载频域特性分析

Frequency Domain Characteristics Analysis for Wind Loads During Construction of Super Large Cooling Tower

以国内在建世界最高220 m超大型冷却塔为对象,基于大涡模拟(Large eddy simulation,LES)方法获得施工全过程冷却塔周围流场和风荷载时程,并将成塔风压分布结果与规范及实测曲线进行对比验证了数值模拟的有效性。在此基础上,对比分析了施工全过程塔筒平均与脉动风压根方差分布特性,系统对比研究了施工全过程风荷载频域特性,主要包括:典型测点风压功率谱特性、升/阻力系数功率谱、典型测点间环向相干性和升/阻力系数竖向相干性,并基于最小二乘法拟合给出随高度变化的典型测点功率谱计算公式。研究表明,施工期与成塔的脉动风荷载能量均集中在低频区,其中塔筒中部脉动风荷载在低频区能量较其他位置弱,随着施工高度的增加:脉动风荷载和层阻力系数功率谱密度函数均呈先减小后增大的趋势,升力系数功率谱在塔筒中下部谱值较大而上部较小,测点脉动风荷载环向相干性以及升/阻力系数竖向相干性均逐渐减弱。主要结论可供此类大型冷却塔施工期设计风荷载取值参考。

Taking the world’s highest 220 m domestic super large cooling tower under construction as the example,the flow field information and the three-dimensional aerodynamic forces during construction period are obtained based on large eddy simulation(LES).The average wind pressure distribution of the entire tower results are compared with the standard and the measured curves to verify the validity of the numerical simulation.On this basis,the average wind pressure and pulsating wind load variance distribution characteristics of the whole construction process of tower drum are contrasted and analyzed.Then the ritual law carrier frequency domain features of the whole construction process are systematically contrasted and studied,which include wind pressure power spectrum features of typical measurement points,the power spectrum of lift and resistance coefficient,ring to the coherence of typical measurement points,and the vertical coherence of lift and resistance coefficient.Finally,the calculation formula of the power spectrum with height for typical measurement points is fitted based on least square method.Studies show that the pulsating wind load energy of the tower under construction and the whole tower are both concentrated in the low frequency area,and the pulsating wind load at the central tower drum is weaker than that in other positions.With the increase of construction height,the power spectrum density function of pulsating wind load and layer resistance shows a trend of decreasing first and then increasing,the power spectrum value of lift coefficient is bigger in the lower part of tower and smaller in the upper part,and the ring to the coherence of typical measurement points and the vertical coherence of lift and resistance coefficient are gradually weakening.Main conclusions can provide a reference for the value designing of the wind load for this kind of large cooling tower during construction.