Acoustic Resonance Phenomenon Research Articles

Experimental Study of Supersonic Inlet Buzz

An experimental study of supersonic inlet buzz is presented. This study was carried out on a mixed compression rectangular inlet model; tests were done at Mach numbers ranging from 1.8 to 3, with and without bleed. Inlet flows were analyzed thanks to Schlieren videos and signal processing of unsteady pressure recordings. Two kinds of buzz were observed: which is thought to correspond to an acoustic resonance phenomenon excited by the presence of a shear layer under the cowl lip (Ferri criterion), and which seems to be triggered by a boundary layer separation on the compression ramps (Dailey criterion). In some cases, little buzz could be virtually suppressed by the introduction of a bleed. The frequency of big buzz is shown to be already present in the flow before the onset of large-amplitude oscillations, which suggests that the underlying mechanism of big buzz, probably linked to acoustics, already exists before buzz starts.

Electronic Ballast with Constant Power Output Controller for 250W MH Lamp

In this paper, an electronic ballast was developed to control a 250W metal halide lamp. To avoid acoustic resonance phenomenon, we calculated the acoustic resonance band and determined the driving frequency from 70kHz to 100kHz. Due to the switching loss of MOSFET, many problems are caused in the inverter circuit during lamp lighting, so we reduced the loss by connecting the capacitor that minimizes the magnitude of the impulsive voltage. In this paper, the main point of research is to find the methods to operate the lamp on the rated output power. After detecting the current and the voltage of the lamp, we changed the driving frequency by adjusting the DC voltage level of the VCO input.

305 流れ方向に密な格子配列管群における気柱共鳴現象と渦放出

In the present paper the attention is focused on similarity between the phenomena of acoustic resonance which occurred in actual boiler plant and that of the two-dimensional model of boiler. We measured a gap velocity, sound pressure level, acoustic mode shape, spectrum and phase delay of velocity fluctuations in the tube banks. As a result it was made clear that the phenomenon of acoustic resonance in the model is similar with that of the actual plant. The relation between vortex shedding phenomena inside of in-line tube banks and acoustic resonance in the model was experimentally examined.

Experimental study on acoustic resonance phenomena in ageing high-intensity discharge lamps

It is widely thought that ageing a metal halide (MH) lamp will result in changes in the acoustic resonance eigenfrequencies but to date no experimental data on this topic has been reported in the literature. A study on the influence of the operating time on the stability of low-wattage MH lamps is now presented. It is shown that the age of a lamp does not affect the fundamental acoustic eigenfrequency values. The upper limit of the frequency of the highest acoustic resonance band at which the arc will become unstable is not affected by the age of the lamp. However, the lamp age does influence the extent of instability inside the lamp with the lamp voltage significantly increasing

Prediction of acoustic resonance phenomena for weapon bays using detached eddy simulation

AbstractIt is argued that acoustic resonance phenomena in open cavities such as weapons bays cannot be adequately predicted through numerical solution of Reynolds averaged Navier-Stokes (RANS) equations. The requirement to resolve the growth of the shear layer instability from the lip of the cavity inevitably implies that turbulence further downstream is resolved while also being modelled thus making RANS over dissipative. Large eddy simulation (LES) models only unresolved scales and a hybrid method combining RANS near walls with LES in the cavity appears a practical alternative to pure RANS. This paper compares computations of the M219 cavity configuration made with unsteady RANS and with the hybrid method known as detached eddy simulation (DES). It is shown that whilst unsteady RANS and DES give very similar predictions for the 1st and 3rd modes of the acoustic resonance the 2nd mode (which is dominant near the centre of the cavity) is absent in the RANS results but well predicted by DES. The 2nd mode is thought to arise from an interaction with vortical structures in the shear layer which are suppressed in the highly dissipative RANS method. The 4th mode, which is much weaker than the other three modes, is over-predicted by DES and under-predicted by a smaller amount in RANS.

Successful Treatment of a Postpolio Tinnitus with Type A Botulinum Toxin

Objective tinnitus is a symptom often observed in patients with chronic hyperactivity of masticatory muscles. We report here the unusual case of a 63-year-old woman who developed a distressing tinnitus related to contractions of reinnervated masticatory muscles. This reinnervation process was caused by a postpolio syndrome that gave rise to an acoustic resonance phenomenon transmitted to the middle ear as an audible sound. The tinnitus was successfully treated with electromyography-guided intramuscular injections of type A botulinum toxin. The intramuscular injection of botulinum toxin was found to be effective in relieving severe and disabling postpolio tinnitus.

617 ポンプシールから発生する水流卓越音の制御

Hydrodynamic tones are radiated from water pumps in some operating condition and the cause of these tone are generated by the self-excited unsteady flow crossing the annular or screw grooves of pump seals. Characteristics of these tone from the annular grooves of seals were experimentally studied by using the test stand for measuring the rotor-dynamics of seals and lubricate bearings with support of the active magnetic bearing. It was made clear that the groove size, the leak flow velocity, the length of seal changed tone frequencies and intensity. The results of study suggest that some acoustic resonance phenomena dominate the generation of the self-excited tone from seal flows. The groove depth, the groove width, the shape of groove entrance and the shaft eccentricity do not have any direct relations to the resonance condition.

A Study on Suppressing Acoustic Resonance of Interaction Tones from a Centrifugal Motor Blower

In a centrifugal blower with diffuser vanes, the noise level may increase at certain rates of revolution. In particular, the phenomenon of acoustic resonance due to tones arising from aerodynamic interaction between the impeller and the diffuser is serious. In this paper, we develop a physical model to describe this phenomenon. The model assumes that the flow paths in both the impeller and the diffuser behave as quasi-one-dimensional acoustic tubes. The model predicts the critical rates of revolution at which resonance occurs, and the prediction of the model is verified by experiments. We also propose an effective method for suppressing the resonance. This involves the use of diffuser vanes with slits. Each slit is located just behind the end of the overlapping region between neighboring vanes. The physical model determines this location. Experiments showed that the method successfully reduces sharp peaks in the noise spectrum.

Self–Oscillations in the Gas Cavity of a Solid Rocket Motor

It is established that self–oscillations in the gas cavity of a solid rocket motor are due to instability and periodic changes of large–scale compact vortex structures in the stagnation zones of the main flow of combustion products. Indirect data of full–scale tests and experimental studies show that compact stagnation zones are formed between the side wall of the gas cavity and the submerged nozzle and near the up bottom of the motor. A procedure was designed to calculate and predict Strouhal numbers and acoustic resonance phenomena in the gas cavity of a motor chamber due to changes of compact large–scale vortex structures.

A Study on Suppressing Acoustic Resonance of Interaction Tones from a Centrifugal Motor Blower. Modeling of Phenomenon and Proposal of Suppression Method.

In a centrifugal blower with diffuser vanes, the noise level may unexpectedly increase at certain numbers of revolutions. In particular, the phenomenon of acoustic resonance due to aerodynamic interaction tones between the impeller and the diffuser is a serious problem. In this paper, we develop a physical model to describe this phenomenon. The model assumes that inner flow paths both in the impeller and the diffuser behave as quasi-one-dimensional acoustic tubes. We constructed a mathematical model to predict critical numbers of revolutions at which resonance occurs, and conducted experiments to verify the model, and the results agree well with the mathematical model. We also propose an effective method for suppressing the resonance in which diffuser vanes with slits are used. Each diffuser vane has a slit located just behind the end of the facing area between neighboring vanes. The location of the slit is determined by the mathematical model. Experiments show that the method successfully reduces keen noise by as much as 8 dB.

Resonant acoustic frequencies of a tandem cascade. Part 1. Zero relative motion

In this paper we study the acoustic scattering between two flat-plate cascades, with the aim of investigating the possible existence of trapped modes. In practical terms this question is related to the phenomenon of acoustic resonance in turbomachinery, whereby such resonant modes are excited to large amplitude by unsteady processes such as vortex shedding. We use the Wiener–Hopf technique to analyse the scattering of the various wave fields by the cascade blades, and by considering the fields between adjacent blades, as well as between the cascades, we are able to take full account of the genuinely finite blade chords. Analytic expressions for the various scattering matrices are derived, and an infinite-dimensional matrix equation is formed, which is then investigated numerically for singularity. One advantage of this formulation is that it allows the constituent parts of the system to be analysed individually, so that for instance the behaviour of the gap between the blade rows alone can be investigated by omitting the finite-chord terms in the equations. We demonstrate that the system exhibits two types of resonance, at a wide range of parameter values. First, there is a cut-on/cut-off resonance associated with the gap between the rows, and corresponding to modes propagating parallel to the front face of the cascades. Second, there is a resonance of the downstream row, akin to a Parker mode, driven at low frequencies by a vorticity wave produced by trapped duct modes in the upstream row, and at higher frequencies by radiation modes (and the vorticity wave) between the blade rows. The predictions for this second set of resonances are shown to be in excellent agreement with previous experimental data. The resonant frequencies are also seen to be real for this twin cascade system, indicating that the resonances correspond to genuine trapped modes. The analysis in this paper is completed with non-zero axial flow but with zero relative rotation between the cascades – in Part 2 (Woodley & Peake 1999) we will show how non-zero rotation of the upstream row can be included.

直流点灯ショートアークメタルハライドランプの音響共鳴に関する一考察

直流点灯ショートアークメタルハライドランプの音響共鳴に関する一考察

Airfoil wake and linear theory gust response including sub- and superresonant flow conditions

The unsteady aerodynamic gust response of a high solidity stator vane row is examined in terms of the fundamental gust modeling assumptions with particular attention given to the effects near an acoustic resonance. A series of experiments was performed with gusts generated by rotors comprised of perforated plates and airfoils. It is concluded that, for both the perforated plate and airfoil wake generated gusts, the unsteady pressure responses do not agree with the linear-theory gust predictions near an acoustic resonance. The effects of the acoustic resonance phenomena are clearly evident on the airfoil surface unsteady pressure responses. The transition of the measured lift coefficients across the acoustic resonance from the subresonant regime to the superresonant regime occurs in a simple linear fashion.

Application de l'A.D.L, pour la mesure du champ de vitesses instationnaires de llecoulement a Ilechappement d'un moteur a combustion interne

We present experimental results of instantaneous velocity measurement, which were obtained by application of the laser Doppler anemometry (L.D.A.) at the exhaust pipe of a reciprocating engine under real working conditions. First of all, we show that the instantaneous velocity is monodimensional along a straight exhaust pipe, and that the boundary layer develops within a 2 mm thickness. We also show that the cylinder discharges in two phases: the blow down period and the final part of exhaust stroke. We also make obvious, that the flow escapes very quickly: its velocity varies between - 100 m/s and 200 m/s within a period shorter than 1 ms; thereby, we do record the acoustic resonance phenomenon, when the engine speed is greater than 3 000 rpm. Finally, we show that in the exhaust pipe the apparent fluctuation-i.e. the cyclic dispersion and the actual turbulence-may reach 15%

Asymptotic solutions for unsteady flow in cascades

Asymptotic methods are presented for obtaining approximate solutions to unsteady flows in oscillating cascades. The formulation is in the framework of linearized potential flow, and the problems considered include low-frequency and low-solidity expansions for subsonic and supersonic cascades. For the supersonic cascade, simple formulas are obtained for the unsteady lift and moment, valid to first order in a frequency parameter. It is shown that terms of successive orders can be obtained by solving a sequence of quasi-static problems, with the effective upwash at each step modified by the lower-order solutions. The approach is in the spirit of matched asymptotic expansions, and different expansions based on different limit processes are sought for the subresonant and superresonant regions. For cascades in subsonic axial flow, the acoustic resonance phenomenon leads to a nonuniformity with respect to the interblade phase angle. The location of the singularity can be moved by suitably redefining the limit process, permitting uniformly valid expansions to be obtained separately for the subresonant and superresonant regions. Numerical comparisons with the full unsteady solution indicate that the present approximations are remarkably accurate in the range of reduced frequencies of interest in aeroelastic analyses.

Some Considerations on the Air Forces on a Wing Oscillating Between Two Walls for Subsonic Compressible Flow

The problem of the determination of the air forces on an oscillating airfoil between plane walls has, until recently, been treated only for incompressible flow. The present paper is concerned with the important effects of compressibility, which may be of significance in such problems as the measurement of oscillating air forces or of wing flutter characteristics in wind tunnels, and in the flutter of airfoils in cascade. The possibility of the existence of an acoustic resonance phenomenon under certain critical conditions is discussed. The integral equation for the compressible case, as obtained by Runyan and Watkins in NACA T N 2552, is reviewed briefly and a method of solving the equation is given. The procedure is applied to a number of selected cases at various Mach numbers and tunnel heights. The effect of the presence of the walls is shown to be very significant near the resonant frequency and, for certain conditions, to be large even at frequencies well removed from resonance.