Tones Produced by a Wire Placed in an Ignited Gas Jet

Abstract

It was found that a wire placed in an ignited gas jet would produce a tone when the velocity of the gas reached a critical value. The tone was amplified by use of a second wire and by use of a photoelectric cell. The relation between the diameter D of the wire, the diameter O of the orifice, the distance d of the wire from the orifice and the critical velocity Ui for the initiation of the tone was found to be of the form OUi = kd/D + C, where k and C are constants. This equation is not linear for values of d less than one centimeter. It appears that a similar relation exists for the critical velocity Uf at which “flaring” starts. The products OUi/ν, where ν is the kinematic viscosity, were found to be nearly the same for the two gases used. At any distance of a wire from the orifice the frequency of the tone was found to be a linear function of the efflux velocity of the gas. The expression for the frequency was found to be of the form N = k/D(U − U0), where k is a constant and U0 is the velocity intercept. The quantity D(dN/dU) has an average value of about 0.047 for wire diameters between 0.04 and 0.1 cm. For a constant frequency the relation between the orifice velocity and the distance was found to be of the form U = Kdn, where n is approximately 12; nO12 is a constant and KO12 nearly constant. An approximate relation between frequency, velocity, and distance is given by N = kU/d12 + C, where k and C are constants. A thin metallic sheet placed against the wire on the downstream side prevents the production of the tone. As the distance between this sheet and the wire is varied the tone ceases at a critical distance, which is a function of the velocity and the diameter of the wire. For a fixed velocity this critical distance is proportional to the square root of the diameter of the wire. It was concluded that the tone is an Aeolian tone modified by the flow of one stream into a similar fluid at rest. An equation of the form N = kU/D was derived on the basis of the Bernard-Karman vortex theory. By comparing experimental with theoretical results it was concluded that for an ignited jet the density varies inversely as the distance from the orifice.