水冷壁管道泄漏声场分布特征数值研究

根据Bloch理论研究了锅炉水冷壁周期表面的声反射行为，指出了水冷壁表面将使入射声波沿多个方向发生散射，其行为类似于反射光栅，其中镜面反射方向的零级衍射波，具有较高的能量份额。炉内水冷壁管道泄漏声场，主要包括泄漏直达声和所在水冷壁面的反射声两部分组成。根据叠加原理和镜像原理，近似计算了水冷壁管道泄漏声辐射的远场空间分布特征。结果表明较高频泄漏声波具有明显的空间指向性特征．在泄漏口正前方声压级(SPL)较高。较低频泄漏声波由于空间干涉效应明显，指向性特征被干涉效应掩蔽，泄漏口正前方的声压级(SPL)甚至有时很低。因此，利用泄漏声强度特征在较低频段不宜对泄漏源进行有效定位，强度定位技术益在较高频段进行，其特征频段与水冷壁管道几何尺寸有关。

A STUDY ON THE TRAIT VALUE OF THE SOUND FIELDS RADIATED FROM A LEAKY HOLE ON THE WATER WALL IN BOILERS

Upon employing the Bloch theorem, reflection behavior of the water-wall interface having periodic height variation is examined for the sound waves in boilers. It reveals that the water-wall interface scatters the incident wave into some different direction waves. It's similar to the reflection gratings. The zero-order diffraction wave is on the direction of mirror reflecting. Its energy is far more than the energy of other order's diffraction waves. The sound field radiated by a leak on the water-wall includes two parts. One is the direct sound wave, and another is the reflection sound wave. By using of the addition theorem and the mirror image theorem, we calculate a distant space sound field distribution of a sound source spurted from a round hole with a homogeneous amplitude on water wall. The results show that the sound radiation at high frequency present obvious character of directivity pattern. There is a higher SPL on the direction of right in front of the leak hole than other direction. Because of the interference effect with the sound waves, character of directivity pattern will be sheltered at low frequencies. Sometimes the SPL on the right direction in front of the leak hole will be very small. So it is difficult to locate the leak position, using the SPL at low frequencies. The locating technique using SPL is propitious to wave at higher frequencies, and its frequency-band is relation to the geometry dimension of the tube on the water-wall.