For the case of a realistic small-scale “double-stream nozzle–high-lift wing” configuration, a previously developed simplified semiempirical method for calculating the low-frequency noise of jet–wing ...interaction is tested. As input data for calculating the noise, we used the results of measuring the amplitude and convective velocity of perturbations in the near field of a turbulent jet near the trailing edge of an extended flap. The measurements were performed with a pair of pressure sensors flush-mounted on the lower surface of the wing model. It is demonstrated that the results of the calculated estimate for the spectral characteristics and directivity of the interaction noise agree well with direct noise measurements in the far field both under static conditions and in the presence of coflow simulating the effect of flight.
Abstrast
The conventional beamforming algorithm has been generalized, making it possible to mutually take into account the data of sequential measurements by one microphone array placed in different ...positions with respect to the sound generation area. When it is impossible to directly use microphone arrays with the required geometry in a synchronous measurement system, the generalized algorithm makes it possible to substitute measurement with an array of complex configuration with a set of measurements using one microphone array sequentially placed in different positions. The modified method is verified and validated by numerical simulations, as well as by the results of experiments in TsAGI’s AC-2 anechoic chamber, where acoustic speakers were used as noise sources.
It is shown that the velocity fluctuation spectra measured using a hot wire in the potential flow region of the near field of a turbulent jet with a coflow can be converted into pressure fluctuation ...spectra. The proposed conversion method is based on the fact that the structure of instability waves, which make a decisive contribution to jet near-field fluctuations, resembles homogeneous one-dimensional waves, which makes it possible to locally link pressure fluctuations and the fluctuations of the streamwise velocity component measured by a hot wire.
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The relationship between velocity and pressure fluctuations in the near field of a subsonic turbulent jet and at its axis is investigated. The data of the measurements of the velocity fluctuations ...at the jet axis and the pressure fluctuations in the jet near-field are analyzed. It is shown that the spectral characteristics of the velocity fluctuations at the axis can be converted to the spectra of the axisymmetric mode of the pressure fluctuations outside the jet. The conversion is based on the use of the eigenfunctions of the pressure fluctuations obtained in solving the stability problem for a cylindrical mixing layer of finite thickness in the locally-parallel approximation.
A new method for separating acoustic and pseudosound pressure fluctuations is proposed, based on analysis of signals at a pair of closely located points, so that the total size of the measurement ...zone is much smaller than the correlation scale of pseudosound perturbations. It is suggested that hydrodynamic fluctuations propagate at a velocity significantly lower than the sound velocity and obey the “frozen-in” perturbation model, which makes it possible, in real time or during data postprocessing, to convert the spatial derivative of the signal into a temporal derivative, which, after time integration, yields an estimate for pseudosound perturbations at the measurement point. A theoretical model of the approach and test results using model examples and numerical simulation data are presented.
Azimuthal decomposition was used to study the azimuthal composition of noise of a jet issuing from a coaxial nozzle. Various combinations of the velocities of the core and bypass jets are considered. ...The features observed in the spectral characteristics and in the shapes of the directivity patterns of individual azimuthal modes are analyzed, in particular, the excess noise of a coaxial jet over the noise of an equivalent fully mixed jet when there is a significant difference in velocities in the outer and inner ducts. It is also shown that the difference between them occurs in all three azimuthal modes, and the main problem for noise simulation is the coaxial jet transition zone.
For a jet located near the wing, instability waves present in jet mixing layer scatter on the wing trailing edge, leading to additional noise generation. In this article, the possibility of reducing ...this noise by active cancellation of natural instability waves has been experimentally studied. The active control system consists of near-field microphones from which the feedback signal is taken, a data processing module for signal filtering, and a high-frequency dielectric barrier discharge plasma actuator. Decrease in pressure perturbations in the near field of a turbulent jet associated with axisymmetric instability waves in a narrow frequency band was demonstrated. It was shown that this reduction leads to a corresponding noise decrease in the far field.
The results of the theoretical and experimental study of the effect of the wing-setting angle on the far acoustic field associated with the wing trailing edge scattering of hydrodynamic near-field ...perturbations of a turbulent subsonic jet are presented. For a model in which the scattering surface is simulated by a half-plane, the analytical dependence of the principal characteristics of the scattering field on the setting angle of the scattered surface is obtained using the Wiener–Hopf technique. An experimental study of the sound field of the “nozzle–plate” configuration using a movable azimuthal microphone array is carried out in TsAGI AC-2 anechoic chamber and a good agreement between the theoretical model and the measurement data is shown.
The use of high-bypass-ratio engines in civil aviation has resulted in the occurrence of an additional noise source associated with noise of interaction between a jet and an airplane wing. A ...theoretical model is proposed for predicting the characteristics of interaction noise based on the near-field parameters for an isolated jet. The required near-field characteristics were obtained experimentally in the AC-2 anechoic chamber of the Central Aerohydrodynamic Institute (TsAGI) using a system of azimuthal microphone arrays. Noise in the far-field zone was also measured for both an isolated jet and a jet with a closely located plate simulating a wing. The results of comparing the directivities and spectra of interaction noise obtained using the proposed model and measured experimentally are in good agreement.
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The classical algorithm for localizing noise sources using a planar microphone array is generalized to the case of its application to dipole-type sources. The developed algorithm was verified and ...validated via data processing of experimental studies of cylinder flow noise and jet–plate interaction noise. We compare the results of localizing dipole noise sources using a planar microphone array employing the developed algorithm and an azimuthal array based on the azimuthal decomposition technique.
