Refraction of Sound from a Point Source Placed in an Air Jet

Abstract

A harmonic point source of sound was placed within the potential core of an air jet and the distortion of its sound field by the jet flow was measured. An axial intensity minimum was observed that increases with increasing velocity, frequency, or temperature. The investigation indicates that the cleft in the heart-shaded directivity pattern of subsonic jet noise can be attributed mainly to refraction.

Influence of Source Interference on the Directivity of Jet Mixing Noise

“…Eqs. (22), (24), and (26) are valid in the acoustic far field of the sources, but the observer position may be located in the geometric near field of the jet.…”

“…The phase ψ q considers the effect of source convection in the flow. ψ r considers the influence of the difference of the retarded times between the two source positions and is defined by equation (24).…”

“…22 The fact that higher frequencies are not observed in the rear arc may have two causes. Firstly, the effects of wave refraction which were experimentally verified by Atvars et al 24,25 are excluded in this simple model. They affect the spectral shape especially for high frequencies for angles close to the jet axis.…”

Development of a Technique for In-Flight Jet Noise Simulation - Part 11

“…This procedure was adopted for 3<A: 0 a<6 using the experimental data taken by Ribner and his students with point sources in jets. 10 Actually the data are available only for k 0 a < 1.25 and, hence, a linear extrapolation of it for k 0 a> 1.25 but less than 6 was used. The test data from our freejet experiments showed a tendency for the refractive dip to saturate, presumably due to turbulent scattering, beyond (k 0 a) greater than 6.…”

Through-transmission imaging of solids in air using ultrasonic gas-jet waveguides

“…T he interaction of acoustic signals with gas jets has been studied by various workers, mainly as a result of trying to understand the acoustics and noise generation by aircraft engines [1]- [4]. It is now known that the presence of high velocity, high temperature gas jets causes sound to be emitted at an angle to the jet axis, with lower amplitudes being radiated along the jet axis (known as a cone of silence).…”