This study aims to make use of two concepts in the field of aeroacoustics; an analogy with relativity, and Geometric Algebra. The analogy with relativity has been investigated in physics and cosmology, but less has been done to use this work in the field of aeroacoustics. Despite being successfully applied to a variety of fields, Geometric Algebra has yet to be applied to acoustics. Our aim is to apply these concepts first to a simple problem in aeroacoustics, sound propagation in uniform flow, and the more general problem of acoustic propagation in non-uniform flows. By using Geometric Algebra we are able to provide a simple geometric interpretation to a transformation commonly used to solve for sound fields in uniform flow. We are then able to extend this concept to an acoustic space-time applicable to irrotational, barotropic background flows. This geometrical framework is used to naturally derive the requirements that must be satisfied by the background flow in order for us to be able to solve for sound propagation in the non-uniform flow using the simple wave equation. We show that this is not possible in the most general situation, and provide an explicit expression that must be satisfied for the transformation to exist. We show that this requirement is automatically satisfied if the background flow is incompressible or uniform, and for both these cases derive an explicit transformation. In addition to a new physical interpretation for the transformation, we show that unlike previous investigations, our work is applicable to any frequency.
Propagation of Nonlinear Acoustic Waves in the Suspension of Ultrasound Contrast Agents Part I: Equation for Counting Resonance Effects and Revealing Acoustic Localization
Damping of acoustic waves in straight ducts and turbulent flow conditions
本文通过在光滑直管道中进行的实验研究，研究了平面声波在湍流充分发展流动中的传播。相干扰动的存在，如在湍流受限流动中的声波，会产生壁面剪应力的振荡。在这种情况下，剪切波被激发并叠加在声波上。湍流剪切应力受剪切波调制，壁面剪切应力受湍流的强烈影响。从实验的观点来看，它导致了一个与频率相关的声学子层厚度和湍流平均流的粘性子层厚度之间的比率严格相关的测量阻尼，后者取决于马赫数。通过减少湍流，粘性子层厚度增加，并且波的传播主要由对流效应控制。在目前的工作中，阻尼和壁阻抗已被提取从测得的复波数，这是最重要的参数，用于表征波的传播。一个实验的方法，被称为迭代平面波分解，已被用来获得的结果。研究是在低马赫数、低亥姆霍兹数和低剪切波数的湍流条件下进行的。其目的是克服某些缺乏实验结果的作者发现的最新模型的平面波传播的湍流，如Knutsson等人。（The effect of turbulence damping on acoustic wave propagation in tubes，Journal of Sound and Vibration，Vol.329，No.22，2010），和Weng et al.（The attenuation of sound by turbulence in internal flow，The Journal of the Acoustical Society of…
