Takaishi Takehisa, Sagawa Akio, Nagakura Kiyoshi, Maeda Tatsuo
Railway Technical Research Institute, Shiga, Japan.
J Acoust Soc Am. 2002 Jun;111(6):2601-8. doi: 10.1121/1.1480833.
As the maximum speed of high speed trains increases, the effect of aeroacoustic noise on the sound level on the ground becomes increasingly important. In this paper, the distribution of dipole sound sources at the bogie section of high speed trains is predicted numerically. The three-dimensional unsteady flow around a train is solved by the large eddy simulation technique. The time history of vortices shows that unstable shear layer separation at the leading edge of the bogie section sheds vortices periodically. These vortices travel downstream while growing to finally impinge upon the trailing edge of the section. The wavelength of sound produced by these vortices is large compared to the representative length of the bogie section, so that the source region can be regarded as acoustically compact. Thus a compact Green's function adapted to the shape can be used to determine the sound. By coupling the instantaneous flow properties with the compact Green's function, the distribution of dipole sources is obtained. The results reveal a strong dipole source at the trailing edge of the bogie section where the shape changes greatly and the variation of flow with time is also great. On the other hand, the bottom of the bogie section where the shape does not change, or the leading edge and boundary layer where the variation of flow with time is small, cannot generate a strong dipole source.
随着高速列车最高速度的提高，气动声学噪声对地面声级的影响变得越来越重要。本文对高速列车转向架部分偶极声源的分布进行了数值预测。采用大涡模拟技术求解列车周围的三维非定常流动。涡旋的时间历程表明，转向架部分前缘处不稳定的剪切层分离会周期性地脱落涡旋。这些涡旋向下游移动，同时不断增大，最终撞击到该部分的后缘。这些涡旋产生的声音波长与转向架部分的特征长度相比很大，因此声源区域可被视为声学紧凑区域。因此，可以使用适应该形状的紧凑格林函数来确定声音。通过将瞬时流动特性与紧凑格林函数相结合，得到偶极声源的分布。结果表明，在转向架部分形状变化很大且流动随时间变化也很大的后缘处存在强偶极声源。另一方面，转向架部分形状不变的底部，或流动随时间变化较小的前缘和边界层，不会产生强偶极声源。
