The wide-band shock associated noise was found to be predominant in the range of pressure ratio between 2.5 and 7, and screech only up to slightly more than 5. For pressure ratios less than 2 or more than 8.5, the jet noise is entirely dominated by turbulent noise.

4. the efflux noise of silencers in the effective pressure range can be calculated according to the pressure dependence of turbulent noise and the correction to the ratio of expansion.

Ever since the fifties, profound theoretical and experimental investigations were spent on the noise production of subsonic and supersonic jets, but little has been done on the turbulent noise of a choked jet.

To solve the signal fading problem induced by atmospheric turbulence in optical wireless system,a reception signal model involved turbulence noise and other multiplicative noise was proposed.

Based on the hydrodynamic stability theory of distorted laminar flow and the kind of distortion profiles on the mean velocity in parallel shear flow given in paper [1], this paper investigates the nonlinear stability behaviour of parallel shear flow, carries on stability calculation taking account of the perturbations of background turbulence noise under certain assumption, and obtains some results in accordance qualitatively with those of experiment for plane Poiseuille flow and pipe Poiseuille flow.

By simulations,the adaptive filter algorithm is shown significantly superior to the filter algorithm only considering speckle noise as multiplicative noise in the presence of speckle and turbulence noise.

The research results presented in this thesis have showed the importance in both practice and theory for the improvement of the low-noise performance of the grooves in hydraulic valve.

In wireless OCDMA communication system, signals that a user receives are interfered by the other user’s signals (which is called multi-user interference or multi-access interference, MAI) and channel noise, like background light and atmospheric turbulence induced by wireless optical communication channel.

The momentum thickness Reynolds number Re_θare 1241, 1635. The near-wall coherent structures in the turbulent boundary layer is the most significance in wall shear turbulent flows.

By the experiments, It is found that the effect is mainly due to the upstream noise radiated through the nozzle exit. The weak nonlinear interaction between upstream noise and downstream turbulence is supposed.

Analysis of Turbulent Noise Spectra of Electrochemical Reactions in Different Experimental Conditions

Results obtained by measuring the turbulent noise in a hydrodynamic channel with the use of piezoelectric composite receivers are reported.

The spectrum of ion-acoustic turbulent noise generated by the driven current and concentrated in a limited cone of angles along the propagation direction of the wave is found.

The dependence of the threshold density of the radiation flux on the angle between the scattering wave vector and the direction of anisotropy of the turbulent noise is described.

A new effect of STBS forbiddenness caused by anomalous turbulent heating of the ions is predicted for a plasma with a high level of turbulent noise.

In wind instruments, the turbulence noise is filtered by the resonances of the pipe.

The distinctiveness of this manner contrast can thus be enhanced by increasing the intensity of turbulence noise in the fricative.

Ever since the fifties, profound theoretical and experimental investigations were spent on the noise production of subsonic and supersonic jets, but little has been done on the turbulent noise of a choked jet. In a previous paper the authors derived the pressure dependence of the latter. In this paper it is shown that a slight modifica-tion of the formula in the above-mentioned paper will make it applicable to subsonic jets too, and an interpretation is obtained for turbulent jet noise in general. From this...

Ever since the fifties, profound theoretical and experimental investigations were spent on the noise production of subsonic and supersonic jets, but little has been done on the turbulent noise of a choked jet. In a previous paper the authors derived the pressure dependence of the latter. In this paper it is shown that a slight modifica-tion of the formula in the above-mentioned paper will make it applicable to subsonic jets too, and an interpretation is obtained for turbulent jet noise in general. From this it is inferred that turbulent jet noise has its origin in the quadrapole radiation of turbulent eddies, the only difference in that, for a choked jet, the turbulence velocity further increases with the stagnation pressure, although the mean jet velocity does not. From this point of view, the rule of increase of the turbulent velocity with increasing stagnation pressure is predicted. This interpretation seems plausible and the noise relations thus derived agree with experiment.

Shock associated noise is an important part of choked jet noise. Sound field and spectra thereof were investigated experimentally by utilizing the heterodyne analysis technique, so that both the screech and the wide-band noise can be recorded and studied. The sound pressures and spectra vary widely with the stagnation pressure, but the overall sound pressure level at 90?to the jet shows good regularity, it is nearly a constant between pressure ratios 3 and 8.5, given by 97 + 201og d, dB, d being nozzle diameter...

Shock associated noise is an important part of choked jet noise. Sound field and spectra thereof were investigated experimentally by utilizing the heterodyne analysis technique, so that both the screech and the wide-band noise can be recorded and studied. The sound pressures and spectra vary widely with the stagnation pressure, but the overall sound pressure level at 90?to the jet shows good regularity, it is nearly a constant between pressure ratios 3 and 8.5, given by 97 + 201og d, dB, d being nozzle diameter in mm., and empirical formulae are given to facilitate the SPL prediction on the whole range of pressures. The wide-band shock associated noise was found to be predominant in the range of pressure ratio between 2.5 and 7, and screech only up to slightly more than 5. For pressure ratios less than 2 or more than 8.5, the jet noise is entirely dominated by turbulent noise. New formulae for screech frequency and peak frequency of wide-band shock associated noise are given, which agree well with experiments. The existance of non-harmonic components in screech is explained. Interference effect seems to exist in the upstream direction between shock associated noise and turbulent noise, but not in the 90°direction. This phenomenon is explained by considering the phase relations of the noise.

Based on the low of the eighth power of speed of M.J.Lighthillthis article has derived the calculating formula for the air dynamic noisepower in the compressor,and analysed the factors to affect the noise,also indicated that the dynamic noise in the compressor mainly comesfrom the valve jet noise; the principle to reduce the dynamic noise isto get a small Reynolds number Re; the emphasis to reduce the noise ison the jet turbulent flow noise;the efficient way to reduce the noiseis to decrease the valve Mach number....

Based on the low of the eighth power of speed of M.J.Lighthillthis article has derived the calculating formula for the air dynamic noisepower in the compressor,and analysed the factors to affect the noise,also indicated that the dynamic noise in the compressor mainly comesfrom the valve jet noise; the principle to reduce the dynamic noise isto get a small Reynolds number Re; the emphasis to reduce the noise ison the jet turbulent flow noise;the efficient way to reduce the noiseis to decrease the valve Mach number.