High Acoustic Excitation Research Articles

Experimental study of a slit in the presence of a bias flow under medium- and high-level acoustic excitations

This work presents an experimental investigation of the acoustic properties of a slit in the presence of a bias flow under moderate- and high-acoustic excitations. Impedance tube experiments are discussed for a geometry inspired by deep punching resulting in a cut in the plate. The acoustic transfer impedance of the plate is discussed for several bias flow velocities, acoustic excitation, and different frequencies. In the range considered for this study, a bias flow appears to have two main effects, globally enhancing the sound absorption of the plate and creating a protective layer downstream of the plate due to the interaction between the slits. A maximum of the enhancement factor is found at a specific ratio between the acoustic velocity and the bias flow velocity. Two simple asymptotic behaviors are found, dominated by the flow or by the acoustic excitation, respectively. The behavior of the inertance is complex. Globally the inertance decreases with decreasing flow Strouhal number while its dependency on the amplitude of the acoustic velocity is less obvious.

Normal incidence sound absorption of parallel absorber at high sound pressure

A finite element model is developed to simulate the acoustic response of the parallel absorber array at high sound intensity. The device consists of an MPP and a rectangular backing cavity which is divided into two sub-cavities with different cavity depths. At high acoustic excitation, a nonlinear impedance model instead of the traditional linear model is adopted such that the effects of jets and vortex rings formed at the exit of orifices on the acoustic properties are taken into account. The normal incident pressure is considered as a main variable of the nonlinear acoustic impedance model. The performance of the MPP absorber array with different designed geometric parameters are studied. Based on the parallel absorption mechanism, the preliminary results show that the MPP absorber array provides good absorption performance with a wider frequency range by comparing with the single MPP absorber. Also, compared with the results obtained in linear regime, a better absorption performance is achieved by the MPP absorber array at high sound intensity due to the higher acoustic resistance. The acoustic behaviors of the MPP absorber array are also studied experimentally under normal incidence. The predicted and measured results show good agreement.

Response of non-premixed swirl-stabilized flames to acoustic excitation and jet in cross-flow perturbations

An investigation into the response of non-premixed swirl-stabilized flames to acoustic excitation and jet in cross-flow (JICF) perturbations was carried out. The fluctuations of OH∗ chemiluminescence emission measured simultaneously with the pressure were used to determine flame describing function (FDF). It could be seen that the three specific conditions exhibited stronger heat release oscillations coupled with pressure fluctuations under acoustic forcing and JICF perturbations, which were expressed by the in-phase delay and positive flame response indices originated from Rayleigh criterion to conduct the stability analysis. Low acoustic excitation amplitude triggered more significant response in the flame heat release rate than high acoustic excitation amplitude at the particular forcing frequency, indicating that nonlinear saturation characteristic of the FDF is also emphasized in JICF. Poincaré map was adopted to analyze the lock-in amplitudes of the dynamics system and JICF effects on combustion instabilities under acoustic forcing frequencies nearby/far from the natural frequency. It was found that lock-in occurred more easily when the forcing frequency was greater than the natural frequency, showing that JICF did not affect the system dynamics due to their little impact on the vortex/flame interactions in this work studied.

Nonlinear Response of Composite Panels Under Combined Acoustic Excitation and Aerodynamic Pressure

A e nite element formulation is presented for the analysis of the large dee ection response of composite panels subjected to high acoustic excitation and aerodynamic pressure at supersonic e ow. The e rst-order shear defor- mation theory is considered for laminated composite plates, and the von Karm´ an nonlinear strain -displacement relations are employed for panel large dee ection response. The e rst-order piston theory aerodynamics and the simulated Gaussian white noise are employed for the aerodynamic and acoustic loads, respectively. The nonlinear equationsofmotion foranarbitrarily laminated compositepanelsubjectedto combined aerodynamicand acoustic pressures are formulated e rst in structure node degrees of freedom. The system equations are then transformed and reduced to a set of coupled nonlinear equations in modal coordinates. Modal participation is dee ned and the in vacuo modes to be retained in the analysis are based on the modal participation values. Numerical results include root mean square values of maximum dee ections, dee ection and strain response time histories, probability distributions, power spectrum densities, and skewness and kurtosis. Results showed that combined acoustic and aerodynamic loads have to be considered for panel analysis and design at high dynamic pressure values.

Nonlinear response of composite panels under combined acoustic excitation and aerodynamic pressure

A finite element formulation is presented for the analysis of large deflection response of composite panels subjected to aerodynamic pressure- at supersonic flow and high acoustic excitation. The first-order shear deformation theory is considered for laminated composite plates, and the von Karman nonlinear strain-displacement relations are employed for the analysis of large deflection panel response. The first-order piston theory aerodynamics and the simulated Gaussian white noise are employed for the aerodynamic and acoustic loads, respectively. The nonlinear equations of motion for an arbitrarily laminated composite panel subjected to a combined aerodynamic and acoustic pressures are formulated first in structure node degrees-of-freedom. The system equations are then transformed and reduced to a set of coupled nonlinear equations in modal coordinates. Modal participation is defined and the in-vacuo modes to be retained in the analysis are based on the modal participation values. Numerical results include root mean square values of maximum deflections, deflection and strain response time histories, probability distributions, and power spectrum densities. Results showed that combined acoustic and aerodynamic loads have to be considered for panel analysis and design at high dynamic pressure values.