RARE-1: Understanding the Physics of Human Whistling

用嘴唇吹口哨是我们大多数人在很小的时候就掌握的一项技能。在许多社会中，吹口哨是成长过程中的一个预期阶段。但多达三分之一的人口不掌握这项技能，这并不是因为缺乏音乐天赋，因为专业音乐家也算在不吹口哨的人之列。吹口哨需要口腔前后许多肌肉的协调，需要嘴唇做出非常精确的形状。最根本的是，尽管这是一种常见的人类功能，但我们仍然不知道声音是如何产生的。类似音色的乐器，如长笛，有一个锋利的边缘，气流可以在那里转向两边。但是一个人的嘴唇没有任何锋利的边缘，也没有空气可以去的其他空间。与笛子一样的乐器不同，口哨也是可逆的，所以当空气从嘴里流出或进入嘴里时，声音都可以产生。关于口哨声流体动力学的基础研究很少，最近一次认真的研究是在50多年前。在本提案中，我们计划使用现代实验技术更新并超越该研究，有五个具体目标：(1)验证声音产生的假设机制，(2)确定过程是否本质上是轴对称的，(3)找到最相关的无量纲参数来控制过程，(4)优化这些参数以适应实际使用，(5)根据物理和优化参数设计乐器，并在音乐教学环境中进行测试。这将是50多年来首次将人体功能作为流体力学问题进行系统研究，主要是通过在多维参数空间上测量声功率放大，并辅以流动可视化和固体结构表征。截面直径和偏心率、剖面直径和偏心率将被添加到其他人研究的参数中，这将使我们能够找到最好地将测量结果分解为简单相关性的无量纲分组。我们假设了人类口哨产生声音的机制，并通过系统测量来验证这些几何参数，加上平均流速、密度和声速，并通过温度控制。可视化将揭示周期性涡脱落是否发生，以及它对物理学的重要性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Whistling with our lips is a skill that a majority of us humans master at an early age. In many societies, whistling is an expected stage in the process of growing up. But as many as one-third of the population do not master the skill, and this is not for lack of musical talent since professional musicians are also counted among non-whistlers. Whistling involves the coordination of many muscles at the front and back of the oral cavity and requires making a very precise shape with one’s lips. Most fundamentally, and despite this being a common human function, we still do not know how the sound is produced. Musical instruments of similar timbre, like the flute, contain a sharp edge where an air jet can be diverted to either side. But a person’s lips do not have any sharp edges, and there are no alternative spaces where the air might go. Unlike flutelike instruments, whistling is also reversible, so that the sound can be produced both when the air is flowing out of or into the mouth. Fundamental research on the fluid dynamics of whistling has been scant, with the last serious effort having taken place more than fifty years ago. In this proposal, we plan to update and go beyond that research using modern experimental techniques, with five specific aims: (1) validation of a hypothesized mechanism for sound generation, (2) determining whether the process is essentially axisymmetric, (3) finding the most relevant dimensionless parameters controlling the process, (4) optimizing those parameters toward practical use, and (5) designing musical instruments based on the physics and optimized parameters, and testing them in a music instruction environment.This will be the first time in over fifty years that this human function is studied systematically as a Fluid Mechanics problem, primarily through measurements of acoustic power amplification over a multidimensional parameter space, aided by flow visualization and solid structure characterization. Cross-sectional diameter and eccentricity, profile diameter and eccentricity will be added to the parameters studied by others, which will allow us to find the dimensionless groupings that best collapse the measurements into simple correlations. A mechanism for sound generation in human whistling is hypothesized, to be validated through systematic measurements involving those geometric parameters, plus average flow velocity, density, and sound speed, controlled via temperature. Visualization will reveal whether periodic vortex shedding occurs, and how important it is for the physics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.