SU445475A1 - The way to create transverse sound pressure in the shell - Google Patents

Description

The invention relates to the production of high-frequency transverse oscillations of the gas flow in the shells and can be used in the field of aviation acoustics, instrument-making, metrology and other areas of the national economy.

The known methods of creating sound pressure of the sound flow are based on the periodic interruption of the jet of compressed gas supplied to the resonator tube.

The disadvantages of such methods are the limited upper limits of the studied frequencies and the difficulty of adjusting the frequency and intensity of oscillations of the gas flow. In addition, using known methods, it is possible to excite longitudinal oscillations of the gas flow in the shells.

The proposed method of creating sound pressure allows to initiate transverse sound vibrations in the shells and significantly expands the range of sound pressure frequencies.

A feature of the method is that it uses

The phenomenon of parametric resonance in thin-walled shells. If in such a shell, blown outside with compressed gas, to excite in any way (for example,

With the help of an electrodynamic vibrator), generic oscillations, the bending (transverse) mode of the shell oscillations can enter into a parametric resonance, the amplitude of which, under certain conditions, reaches a considerable value. These lateral oscillations of the resonator tube are transferred to the gas flow and are affected by

on the studied obrlochvu, inside of which the resonator pipe is located coaxially with it.

It is advisable to excite the oscillations in the resonator with an electrodynamic vibrator, the excitation winding which is fed through the amplifier from the sound frequency generator, which allows the frequency and amplitude of the excited oscillations to be easily and smoothly controlled.

The drawing shows a diagram of the device that implements the method.

The resonator tube I, which is a thin-walled shell, is mounted on the electrodynamic vibrator platform 2 along the floor of the oscillations excited by it inside the shell 3 and coaxially with it. Compressed gas is supplied to the gap between the shell 3 under test and the pipe — resonator I. The resonator tube is excited by a longitudinal periodic load asitiwt (a is the amplitude, cx) is the frequency). In this case, in the bending (transverse) form of oscillations of the resonator tube, parametric oscillations occur, which are transmitted from the resonator tube to the gas sunspot, and from there to the shell under study. The excitation frequency tx must be chosen so that it coincides or is a multiple of one of the natural vibration frequencies of the resonator tube. In this case

In the resonator tube, a parametric resonance occurs with the shape of b Sin (in - amplitude, Loo

- frequencies, where L -, 1,2, 3 ...). The intensity of these fluctuations is highest at D%. Since a thin-walled resonator tube has a rather dense spectrum of natural frequencies and there are whole areas of its dynamic instability depending on the parameter L, the transverse oscillations of the gas flow in a fairly wide continuous spectrum can be excited by this method. At the same time, the frequency and intensity of gas oscillations are easily and smoothly controlled by changing the current in the excitation winding of the electrodynamic vibrator.

PRINCIPLES IGI

A method of creating transverse sound pressure in the casing by exciting parametric oscillations in a resonator pipe, characterized in that, in order to expand the frequency range of sound pressure, a stream of compressed gas is directed into the gap between the resonator pipe and the casing, and longitudinal oscillations in the resonator pipe and change their frequency and intensity prior to the onset of parametric resonance.