Park Jong Beom, Mongeau Luc
Ray W Herrick Laboratories, School of Mechanical Engineering, Purdue University, 140 S. Intramural Drive, West Lafayette, Indiana 47907-2031, USA.
J Acoust Soc Am. 2007 Jan;121(1):442-55. doi: 10.1121/1.2401652.
The quasisteady approximation is often made in the study of phonatory aerodynamics to facilitate the modeling of time-varying air flows through the self-oscillating vocal folds. The unsteady, pulsating flow is approximated by a sequence of steady flows through representative configurations of the vocal folds at rest. Previous studies have discussed the accuracy of this approximation for a range of orifice geometries, and flow conditions. The purpose of the present study was to further evaluate the quasisteady approximation experimentally using an improved procedure, from a direct comparison between the discharge coefficients of steady jets through fixed orifices and unsteady jets through modulated orifices of identical shape, area, and transglottal pressures at a given time. Life-scale convergent and divergent glottis-shaped rubber orifices were used in a rigid-walled tube and a low Mach number flow representative of human phonation. It was found that the quasisteady approximation is valid during 70% of the duty cycle, when the Reynolds number was above 3000, for a frequency of oscillations of 100 Hz. The steady form of Bernoulli's equation along a streamline, and Bernoulli's flow obstruction theory were found to be reasonably accurate for the unsteady flows. These models break down at low Reynolds numbers, near the beginning and the end of the duty cycle, due to viscous effects and to the influence of flow displaced by the motion of the walls.
在发声空气动力学研究中，常采用准稳态近似法，以便对通过自激振荡声带的时变气流进行建模。不稳定的脉动流通过一系列静止声带的代表性构型的稳定流来近似。先前的研究已经讨论了这种近似对于一系列孔口几何形状和流动条件的准确性。本研究的目的是通过一种改进的程序，从在给定时间通过固定孔口的稳定射流与通过形状、面积和跨声门压力相同的调制孔口的不稳定射流的流量系数的直接比较中，进一步通过实验评估准稳态近似。在刚性壁管中使用了与真实尺寸相同的收敛和发散声门形状的橡胶孔口，以及代表人类发声的低马赫数流。研究发现，当雷诺数高于3000且振荡频率为100Hz时，在占空比的70%期间准稳态近似是有效的。沿流线的稳态伯努利方程形式以及伯努利流阻塞理论对于不稳定流来说相当准确。由于粘性效应以及壁面运动所排挤的流动的影响，这些模型在低雷诺数下、在占空比的开始和结束附近失效。
