Theoretical Simulation And Experimental Study On The Sound Characteristics Of Reed Whistles

Reed whistle as a form of edge structure which is a effective method of engineering application from laboratory to project. Liquid reed whistle gradually cause concern, it has many advantages, such as simple structure, low cost, low energy consumption and so on, so it can deal with wastewater, oil viscosity and heavy oil emulsification in engineering application.Although the study of edge sound generator has a history of a century and a half, but mainly in instrument applications. The existing research on hydrodynamic generator principally focused on the theoretical research, and most is based on gas dynamic research, less liquid studying, so actual application advance basic research. This article discusses the sound mechanism and voice characteristics mainly from the theoretical simulation and experimental research, the specific works are as follows:(1) Liquid reed whistle generator works in turbulent state, and the jet is a complex fluid dynamics problems, which increase the difficulty for researching. In order to study the sound characteristics of reed whistle, so the jet speed is below the turbulent speed. Simulate the jet flow, vortex and pressure distribution of the reed’s tip and two sides by the finite element software.Simulation results show that the jet has alternating joggle characteristic, and separates at the tip of the reed, which provides certain conditions for vortex’s generation. For different inlet velocity, nozzle thickness and length of reed the both sides of the reed can produce significant asymmetric vortex street, but the rotation direction is different from the Karman vortex street. The maximum pressure of reed at the tip, and the maximum and minimum pressure alternately distribute on the two sides of reed.(2) Using the two-way fluid-structure interaction module of the finite element software to simulate the influence of vibration and stress of reed under the different inlet pressure, spray distance and different length of reed.Simulation results show that under different inlet pressure, the amplitude of the reed and stress increase with the inlet pressure increase. The amplitude of the reed steadily periodic changes when the vibration is stabilize. The standoff distance is changed, the vibration amplitude changes. Increasing the length of the reed, the initial vibration amplitude increase for different shapes reed, and the stress also increase before they are reduced. The maximum stress is near the screw hole of the reed. (3) In the experiment, we study the influence of basic frequency and sound pressure level of reed whistle under different pressure, spray distance, length and thickness of the reed using control variate method.Experimental results show that the fundamental frequency of the reed whistle decreases with the increase of inlet pressure or standoff distance, the results is consistent with Brown’s empirical formula. For difform reed, the longer of reed, the lower of the fundamental frequency. Because the longer reed is easily vibrated, and the vibration period is longer, so the frequency is smaller. The fundamental frequency increase with the increase of the thickness of reed, this is because the thicker of reed, the smaller vibration period, so the frequency is bigger. The experimental results are coincided with reed whistle experience formula.For different parameters, the fundamental frequency of trapezoidal reeds is close to T reed, and bigger than the rectangular reed. This is because the split width of trapezoidal reeds and T reed are20mm and close to the width of the nozzle. When the jet impact on the reed, the force is concentrated and has less energy dissipation. From split to the end of reed width gradually widen, the reed is easy to vibrate, so the fundamental frequency and sound pressure level is greater than the rectangular reed’s, it provides a theoretical basis for structure optimization of reed whistle.The influence of inlet pressure and the reed length on the reed is fairly discipline, but for spray distance and the thickness of reed without certain regularity, this is because under the different parameters, the vibration frequency of the reed is different, and some of the resonant frequency is more, therefore the sound pressure level is larger, and the sound pressure level is smaller.Interestingly, there are many voice frequencies in spectrum and satisfy the doubling relationship between the certain frequency. We also show the spectrum diagram without reed, turned out to be no resonance peak. It shows that the voice is indeed generated by the reed vibrating.