Flow induced oscillation in a cavity and its suppression by means of acoustic excitation were studied both experimentally and numerically. In the experiment it was found that with the leading edge pure tone excitation...Flow induced oscillation in a cavity and its suppression by means of acoustic excitation were studied both experimentally and numerically. In the experiment it was found that with the leading edge pure tone excitation at some frequencies and intensities. the flow-induced oscillation in the cavity could be greatly suppressed. Cavity flows both with and without acoustic excitation were studied by solving the 2-D time-dependent Reynolds averaged Navier Stokes equations using explicit predictor-corrector difference algorithm of MacCormack. Effects of turbulence were simulated via Cebeci-Smith turbulence mode with relaxation modification. The computational and experimental results are compared. and good agreement is obtained.展开更多
An experimental study of cavity oscillating flow carried out on subsonic wall jet facilities in an anechoic room is summarized. The jet exit Mach number range is from 0.2 to 0.8. The effects of the flow Mach number (...An experimental study of cavity oscillating flow carried out on subsonic wall jet facilities in an anechoic room is summarized. The jet exit Mach number range is from 0.2 to 0.8. The effects of the flow Mach number ( Ma ) and the cavity depth ( D ) on the oscillation are studied. It is found that for L/D =4, (shallow cavity), the oscillation is mainly due to the self exciting of the free shear layer above the cavity opening, for L/D =2, the acoustic resonance is responsible for the oscillation. Preliminary tests are performed to study the suppression effect of the leading edge tone excitation on cavity flow, and considerable reduction of oscillation has been achieved when Ma ≤0.6.展开更多
Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. ...Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.展开更多
In the present paper,the attention is focused on the characteristics of lightweight materials collection in the duct using acoustic resonance phenomena.The acoustic resonance was excited by using a controlled speaker ...In the present paper,the attention is focused on the characteristics of lightweight materials collection in the duct using acoustic resonance phenomena.The acoustic resonance was excited by using a controlled speaker at the middle of a test duct.We measured the sound pressure level,frequency response characteristics,acoustic damping ratio,mode shape,and lightweight materials response to acoustic resonance excited by a speaker.As a result,the acoustic damping ratio decreased as the mode number of acoustic resonance increased.The tissue strips and the lightweight materials were collected at the node of acoustic pressure when the acoustic resonance was excited.It was made clear that it is possible to control lightweight materials using acoustic resonance excited by a speaker.展开更多
To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 (1956)] is ...To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 (1956)] is applied to calculate the energy transition rates of Vibrational- Vibrational (V-V) and Vibrational-Translational (V-T) energy transfer in gas mixtures. The results of calculation for the multi-relaxation processes in various gas mixtures, consisting of carbon dioxide, methane, chlorine, nitrogen, and oxygen at room temperature, demonstrate that the acoustic energy stagnated in every vibrational mode is coupled with each other through V-V energy exchanges. The vibrational excitation energy will relax through the V-T de-excitation path of the lowest mode because of its fastest V-T transition rate, resulting in that only one absorption peak can be measured for most of excitable gas mixtures. Thus, an effective model is provided to analyze how the vibrational energy transition rates affect the characteristics of acoustic relaxation processes and acoustic propagation in excitable gas mixtures.展开更多
文摘Flow induced oscillation in a cavity and its suppression by means of acoustic excitation were studied both experimentally and numerically. In the experiment it was found that with the leading edge pure tone excitation at some frequencies and intensities. the flow-induced oscillation in the cavity could be greatly suppressed. Cavity flows both with and without acoustic excitation were studied by solving the 2-D time-dependent Reynolds averaged Navier Stokes equations using explicit predictor-corrector difference algorithm of MacCormack. Effects of turbulence were simulated via Cebeci-Smith turbulence mode with relaxation modification. The computational and experimental results are compared. and good agreement is obtained.
文摘An experimental study of cavity oscillating flow carried out on subsonic wall jet facilities in an anechoic room is summarized. The jet exit Mach number range is from 0.2 to 0.8. The effects of the flow Mach number ( Ma ) and the cavity depth ( D ) on the oscillation are studied. It is found that for L/D =4, (shallow cavity), the oscillation is mainly due to the self exciting of the free shear layer above the cavity opening, for L/D =2, the acoustic resonance is responsible for the oscillation. Preliminary tests are performed to study the suppression effect of the leading edge tone excitation on cavity flow, and considerable reduction of oscillation has been achieved when Ma ≤0.6.
文摘Acoustic wave exhibits inherently different characters of propagation, excitation and coupling in phonon band-gap materials in which its elastic, piezoelectric constants are modulated in order of acoustic wavelength. These kinds of novel materials were exampled by phononic crystals with elastic constants modulation, acoustic superlattice and ionic-type phononic crystals with piezoelectric constants modulation. In this talk, phonic crystals were constructed with steel rods embedded in air. Negative refraction of acoustic wave was both experimentally and theoretically established in the phononic crystals. The propagation of acoustic wave in the crystals show acoustic band structures because the waves are strong scattered at the Brillouin Zone Boundaries, analogy to electron band structure in real crystals and photonic band structure in photonic crystals. In the acoustic superlattice, ultrasonic waves could be excited by applied alternative electric fields by piezoelectric effect. The frequency, mode and amplitude of the excited wave are determined by the microstructured parameters of the acoustic superlattice at the condition of phase matching. Ionic-type phononic crystals describe the coupling between superlattice phonon and electromagnetic wave. The coupling process resulted in the polariton with a dispersion relation totally different from that of both superlattice phonon and E-M waves, analogy to the polariton of the ionic crystals but in microwave instead of infrared light. These microstructural dielectric materials show artificial abnormal properties and will find novel application in ultrasonic devices and microwave devices.
基金supported by a research grant from Harada commemorative foundation
文摘In the present paper,the attention is focused on the characteristics of lightweight materials collection in the duct using acoustic resonance phenomena.The acoustic resonance was excited by using a controlled speaker at the middle of a test duct.We measured the sound pressure level,frequency response characteristics,acoustic damping ratio,mode shape,and lightweight materials response to acoustic resonance excited by a speaker.As a result,the acoustic damping ratio decreased as the mode number of acoustic resonance increased.The tissue strips and the lightweight materials were collected at the node of acoustic pressure when the acoustic resonance was excited.It was made clear that it is possible to control lightweight materials using acoustic resonance excited by a speaker.
基金supported by the National Natural Science Foundation of China(61461008,61371139,61571201,61540051)the China Scholarship Council Project(201708525058)+1 种基金the National Science Foundation of Guizhou Province,China(Qian Ke He J Zi[2015]2065),Qian Ke He LH Zi[2014]7361)the Recruitment Program of Guizhou Institute of Technology(XJGC20140601,XJGC20150107)
文摘To research the correlation between vibrational energy transition rates and acoustic relaxation processes in excitable gases, the vibrational relaxation theory provided by Tanczos [J. Chem. Phy3. 25, 439 (1956)] is applied to calculate the energy transition rates of Vibrational- Vibrational (V-V) and Vibrational-Translational (V-T) energy transfer in gas mixtures. The results of calculation for the multi-relaxation processes in various gas mixtures, consisting of carbon dioxide, methane, chlorine, nitrogen, and oxygen at room temperature, demonstrate that the acoustic energy stagnated in every vibrational mode is coupled with each other through V-V energy exchanges. The vibrational excitation energy will relax through the V-T de-excitation path of the lowest mode because of its fastest V-T transition rate, resulting in that only one absorption peak can be measured for most of excitable gas mixtures. Thus, an effective model is provided to analyze how the vibrational energy transition rates affect the characteristics of acoustic relaxation processes and acoustic propagation in excitable gas mixtures.