﻿ 高速铁路隧道出口微气压波声学特性计算分析

高速铁路隧道出口微气压波声学特性计算分析Acoustic Characteristics of Micro-Pressure Wave at the High Speed Railway Tunnel Exit

Abstract: The micro-pressure wave will be generated when the compression wave propagates to the tunnel exit. In some cases, there will be a sonic boom at the tunnel exit, which has a negative impact on the surrounding environment. In order to analyze the causes of the sonic boom at tunnel exit, the large eddy simulation method was used to calculate the parameters of the flow field of tunnel exit. Based on the Lighthill acoustic analogy theory, the finite element method was used to calculate the acoustic characteristics of micro-pressure wave, and the audibility threshold of human was introduced to analyze the mechanism of the sonic boom phenomenon at the tunnel exit. In the calculation model of this paper, the micro-pressure wave sound fields of the tunnel exit under different train speeds were compared. It is found that when the speed of the train is higher than 300 km/h, the sonic boom will occur.

1. 引言

Figure 1. The generation process of micro-pressure wave at tunnel exit

2. 研究方法

2.1. 微气压波流场计算方法

2.2. 微气压波声场计算方法

2.2.1. Lighthill声类比理论

Lighthill根据流体流动的连续性方程和动量方程，直接推导得到了将流体与声波动相联系的声学波动方程，并被命名为Lighthill方程。Ffowcs Williams和Hawkings仿照Lighthill方程的推导方法，考虑运动边界对噪声的影响，根据广义格林函数给出了物体表面存在非定向运动的声场FW-H方程 [13] ：

(1)

FW-H方程右侧A项被视作四极子源项，B项视作偶极子源项，C项视作单极子源项。在计算隧道出口微气压波噪声时，由于微气压波是隧道内压缩波向出口外部空间快速释放产生的，并且当压缩波传播至隧道出口时，并不会引起气体明显的宏观流动，因此计算时可忽略偶极子源的影响；此外，单极子源与壁面的法向气流脉动速度相关，流场计算时将隧道出口壁面看作刚体，不会产生垂直于壁面方向的气流振动，因此计算时同样不考虑单极子源。

2.2.2. 有限元法求解声波方程

(2)

(3)

2.2.3. 完美匹配层

3. 微气压波声学计算模型的建立

Figure 2. Partial grid of train-tunnel model at the entrance of tunnel

4. 隧道出口外部声场分析

5. 隧道出口微气压波音爆成因分析

Figure 3. Micro-pressure wave at the tunnel exit

Figure 4. Schematic of Micro-pressure wave calculate domain

Figure 5. The acoustic boundaries of domain

Table 1. Boundary condition type and parameter setting of calculate domain

Figure 6. Distribution of SPL of micro-pressure wave at tunnel exit at different frequencies (unit: dB)

Figure 7. The SPL line of micro-pressure at tunnel exit

Figure 8. The equal-loudness curve

Figure 9. The SPL line of micro-pressure at tunnel exit

6. 结论

1) 隧道出口微气压波噪声声源可类比为四极子源的发声；

2) 微气压波噪声频率主要集中在20 Hz以下，当频率高于100 Hz时微气压波噪声极易被环境噪声淹没；

3) 在长度为500 m、阻塞比为0.2的隧道中，当列车进入隧道的速度高于300 km/h时，引起的隧道出口外微气压波噪声将会出现人耳可听的音爆现象。

4) 计算分析是基于日本新干线E2车型建立的简化计算模型，若考虑缓冲结构，并且隧道长度和阻塞比的不同时，可能会得到不尽相同的结论。

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