单个椭球颗粒声散射数值研究

Numerical research on acoustic scattering by a single prolate spheroid particle

以刚性/液体颗粒和气泡为例,开展椭球颗粒声散射数值研究.运用边界元法研究刚性颗粒的声散射特性,验证该方法的可行性,计算并分析在长短轴比2∶1和3∶1,无因次尺寸参量ka小于10条件下刚性椭球颗粒散射声压.鉴于边界元法的局限性,对液体颗粒和气泡,则采取一种声散射函数近似计算方法.以液体椭球算例验证计算程序,之后预测椭球气泡随不同无因次尺寸参量、长短轴比、入射角的散射声压变化趋势,比较椭球和球形气泡散射声压分布,并对散射截面变化进行探讨.结果表明:对于刚性颗粒,在无因次参量ka大于4后前向散射效应占主要地位,随长短轴比值增加散射旁瓣增强.对于气泡,当椭球趋近于球体时,将本文结果与球体散射声压比较,发现入射角90°时吻合度最高.此外,当无因次参量和入射角不变时,前向散射随长短轴比的增大而增强.表现出与刚性颗粒类似的散射旁瓣随长短轴比的增加而增强,能量向前集中的特征,但散射截面减小.

The purpose of this paper is to investigate acoustic scattering by a prolate spheroid particle.As a verification of the feasibility,the BEM （Boundary Element Method ）is first introduced for calculating acoustic scattering by a rigid spherical particle,which yields consist results with the theoretical values.Then the acoustic pressure distributions of the rigid prolate spheroid particle are presented when the aspect ratio and non-dimensional parameter change.However,due to the limitation of BEM,another method is introduced for calculating acoustic scattering of weak and gas fluid spheroid,which is characterized by approximating the acoustic scattering function. To validate the accuracy,the calculated reduced target strength of weak fluid is compared with the results shown in a previous paper.Then the acoustic scattering pressure distributions of bubbles（i.e.gaseous particles）are illustrated, corresponding to varied incident angles,aspect ratiosand non-dimensional parameters.The variation trends of thenbsp;scattering cross section are discussed too.In the case of bubbles,it is found that when the incident angle and non-di-mensional parameter remain unchanged,the forward scattering grows as the axial ratio increases.When the non-di-mensional parameter is far below 1 ,the scattering pressure distributes uniformly at each angle.For rigid particles and bubbles,it is shown that the forward scattering would gradually dominate when the non-dimensional parameter exceeds 4,the scattering side lobes will be enhanced when the axial ratio increases,while the scattering cross-section will decrease.