Department of Mechanics, Linné FLOW Centre, KTH Royal Institute of Technology, Stockholm, SE-10044, Sweden.
Department of Mathematics and Systems Analysis, Aalto University, Aalto, FI-00076, Finland.
J Acoust Soc Am. 2019 Apr;145(4):2049. doi: 10.1121/1.5095250.
Voiced speech consists mainly of the source signal that is frequency weighted by the acoustic filtering of the upper airways and vortex-induced sound through perturbation in the flow field. This study investigates the flow instabilities leading to vortex shedding and the importance of coherent structures in the supraglottal region downstream of the vocal folds for the far-field sound signal. Large eddy simulations of the compressible airflow through the glottal constriction are performed in realistic geometries obtained from three-dimensional magnetic resonance imaging data. Intermittent flow separation through the glottis is shown to introduce unsteady surface pressure through impingement of vortices. Additionally, dominant flow instabilities develop in the shear layer associated with the glottal jet. The aerodynamic perturbations in the near field and the acoustic signal in the far field are examined by means of spatial and temporal Fourier analysis. Furthermore, the acoustic sources due to the unsteady supraglottal flow are identified with the aid of surface spectra, and critical regions of amplification of the dominant frequencies of the investigated vowel geometries are identified.
语音主要由声源信号组成，该信号通过上呼吸道的声学滤波和通过流场中的扰动产生的涡激声进行频率加权。本研究调查了导致涡脱落的流动不稳定性，以及在声带下游的声门上区域中相干结构对于远场声音信号的重要性。通过对从三维磁共振成像数据获得的真实几何形状的声门狭窄处的可压缩气流进行大涡模拟。通过声门的间歇性流动分离，通过冲击涡旋来引入非定常表面压力。此外，与声门射流相关的剪切层中会产生主要的流动不稳定性。通过空间和时间傅里叶分析来检查近场中的空气动力学扰动和远场中的声信号。此外，借助表面谱识别由于非定常声门上流动引起的声源源，并识别所研究元音几何形状的主导频率的放大关键区域。
