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The effect on the generation of jet noise by the secondary air induction of a modified jet nozzle is analyzed. It is shown that the combination of the secondary air with the primary jet air creates a new jet stream of larger area, lower velocity, and lower noise generation. The decrease in noise radiation is found in terms of the area of the combined jet stream. Detailed check of the theory is not possible at present because measurements of the areas of the combined jet streams have not been generally made along with measurements of the noise. However, it is possible to estimate the upper limit of the appropriate jet stream area in order to obtain the upper limit on noise reduction. The upper limit on noise reduction obtained from the theory is consistent with existing measurements. Qualitative conclusions from the theory with respect to the spectrum and directivity of the noise radiated by jets with modified nozzles are in accord with measurements. [ABSTRACT FROM AUTHOR]

Owing to the inherent nonlinearity of the equations of motion for a perfect fluid, two or more sound waves passing through a common region will, in general, interact with one another and give rise to scattered waves. In this paper, a source function is obtained for the lowest order scattering process which is quadratic in the primary field variables. This function is rewritten in a form that demonstrates that no scattered waves exist outside the region of interaction of two sound beams intersecting each other at right angles. Furthermore, it is demonstrated that no such scattered waves exist when the two beams intersect at the angle θ = -cos-11/2ρ0c0-2d2p/dρ2ρ = ρ0, where ρ, c, and p stand for the density, sound velocity and pressure, respectively, and the subscript 0 means ambient values of these quantities. The interfering effect of pseudo-sound, induced by radiation pressure, is suggested as an explanation for the results of Ingard and Pridmore-Brown, who have reported recently what they believe to be scattered waves from the interaction region of two sound beams intersecting each other at right angles. [ABSTRACT FROM AUTHOR]

An expression obtained (1951) by the author for the radiation force on a scattering obstacle with arbitrary normal impedance is now shown to be valid for any scattering obstacle. The derivation of the final expression for the force in terms of the asymptotic scattering function for the obstacle in the field of an incident plane wave is accomplished by taking into account the interaction of the incident wave with the scattered wave. Thus the former assumption of a perfectly collimated beam (1951) is avoided by considering the incident plane wave to be of infinite extent. The result for the force in the direction of the incident wave is F∥ = c0-1power scattered+power absorbed-∫Γs cosθdA where c0 is the velocity of sound, Γs is the magnitude of the mean scattered intensity, θ is the angle formed between the incident and scattered waves. This is the same result as that obtained in 1951. The expression given in 1951 for the force perpendicular to the incident wave is correct only for an object which scatters in a restricted way. The correct general expression for the perpendicular component of the force is F⊥ = - c0-1∫Γs cosβdA in which β is the angle formed between F⊥ and Γs. [ABSTRACT FROM AUTHOR]

Starting from the Navier-Stokes equations, general equation governing the generation of vorticity R is obtained: ∇2R = μ0-1∇ × ∇ · <ρ0uu>, wherein R is the time-independent vorticity in the Eulerian frame and <ρ0uu> is the average value of Reynolds' stress dyadic. The solution to this vorticity equation, when properly transformed to the particle coordinates, is shown to be divergence free. A specialization of the vorticity equation to the case of solenoidal first-order motion is shown to lead to the generating term employed by Rayleigh and by Schlichting; a specialization to the case of irrotational first-order motion is shown to lead to the generating term employed by Eckart. The sum of the two specialized driving terms does not equal the general term, indicating that the contributions to vorticity from rotational and compression effects are not independent of one another. The theory is applied to find the streaming generated by a well-defined beam of sound giving results agreeing with Eckart and with Markham. However, when it is applied to a two-dimensional standing wave problem, the configuration of the streaming velocity in the boundary layer is found to differ from the results obtained by Rayleigh. Finally, the effect on streaming of a time-dependent viscosity coefficient is examined. [ABSTRACT FROM AUTHOR]

The one-dimensional wave equation is discussed to the second order of approximation by means of a transformation that carries the equation from the Eulerian to the Lagrangean form. Airy's solution to this equation in Lagrangean form has been shown by Fubini to be an excellent approximation to an exact solution of Earnshaw's equation of motion; therefore, Airy's solution is chosen as the basis for much of this discussion. An expression for the local mean hydrostatic pressure in a plane progressive wave is obtained by transforming Airy's solution from particle to local coordinates. In a similar way, the particle velocity in fixed coordinates is shown to possess a time-independent component proportional to, and in a direction opposite to, the intensity vector This d.c. counter-velocity is predicted without recourse to viscous forces and is compatible with zero average mass velocity. For a sound pressure level of 151 decibels in air there should exist a steady particle velocity of 1 cm/sec. Small particles suspended in the field can, under certain circumstances, acquire this velocity. An approximate treatment is suggested for handling second-effects arising from stationary field configurations. The influence of viscosity is discussed qualitatively. One purpose of this paper is to correlate work in the field which has not so far been published in this country. [ABSTRACT FROM AUTHOR]

The generation of transient signals by the propagation of large-amplitude pulses has been investigated. Measurements of the transient signal along the axis of propagation of 10-MHz pulses in carbon tetrachloride confirm the validity of the theoretical treatment of Berktay [J. Sound Vibration 2, 435-461 (1965)]. Data are also presented for the angular dependence of the transient signals generated by 20-MHz pulses in water. [ABSTRACT FROM AUTHOR]

This paper presents the theory of highly directional receivers and transmitters that may be 'constructed' with the nonlinearity of the equations of fluid motion. [ABSTRACT FROM AUTHOR]

It is proved that a linearization of the hydrodynamic equations in the manner of Oseen does not lead to a description of the steady flow phenomena which occur in connection with oscillatory flow past solid obstacles. [ABSTRACT FROM AUTHOR]

The recognition of a signal having asymmetric wave form or harmonically related line structure will be discussed. A general consideration will be given to the average Av when F(t) consists of a signal plus noise. A simple circuit for taking the average when n - 1 consists of two square law rectifiers connected in parallel. The application of this circuit to the recognition of a signal consisting of fundamental and second harmonic terms will be treated in detail. [ABSTRACT FROM AUTHOR]