On a Hydrodynamic Source of Self-Excitation of Narrow-Band Disturbances in a Wind Tunnel.

A study has been made of the occurrence of intense narrow-band components in the spectra of pressure pulsations in a wind tunnel. It has been established that the high level of acoustic emission in auto-oscillations is a consequence of negative static-pressure gradients inside the nozzle and the change in the regime of wall shear flow of an incompressible medium, of the formation of large-scale coherent structures, and of resonance phenomena. It has been noted that the azimuthally nonuniform topology of large-scale transient-flow structures emitting sound and implementation of not a single resonance are responsible for the existence of ensembles of components of an undesirably high level in the pressure-pulsation spectra in the tunnel. One possible method of fighting the considered sound emission generating auto-oscillations has been indicated. [ABSTRACT FROM AUTHOR]