The problem of sound generation by vortices interacting with an arbitrary body in a low-speed flow has been investigated by the method of matched asymptotic expansions. For the purpose of this report, it is convenient to divide the problem into three parts. In the first part the mechanism of the vortex/body interaction, which is essentially the inner solution in the inner region, is examined. The trajectories for a system of vortices rotating about their centroid are found to undergo enormous changes after interaction; from this, some interesting properties emerged. In the second part, the problem is formulated, the outer solution is found, matching is implemented, and solutions for acoustic pressure are obtained. In the third part, Fourier integrals are evaluated and predicated results presented. An examination of these results reveals the following: (a) the background noise can be either augmented or attenuated by a body after interaction, (b) sound generated by vortex/body interaction obeys a scaling factor, (C) sound intensity can be reduced substantially by positioning the vortex system in the "favorable" side of the body instead of the "unfavorable" side, and (d) acoustic radiation from vortex/bluff-body interaction is less than that from vortex/airfoil interaction under most circumstances. Kao, Hsiao C. Glenn Research Center RTOP 522-31-23...

Table of contents

This book contains a thorough and unique record of recent advances in the important scientific fields fluid–structure interaction, acoustics and control of priority interest in the academic community and also in an industrial context regarding new engineering designs. It updates advances in these fields by presenting state-of-the-art developments and achievements since the previous Book published by Springer in 2018 after the 4th FSSIC Symposium. This book is unique within the related literature investigating advances in these fields because it addresses them in a complementary way and thereby enhances cross-fertilization between them, whereas other books treat these fields separately.

This text records the proceedings of the IUTAM Symposium held in Aachen in 1997. It reviews theories based on asymptotic expansions and gives an insight into new computational methods. Some applications of these methods demonstrate their capability, for example the analysis of core structures with axial variation, the description of the interaction of filaments with a solid body and of sound generation by vortex rings, the theoretical approach to the reduction of drag by manipulating vortex structures in shear layers, the numerical simulation of merging vortex rings and of bubble-type vortex breakdown in a tube, and investigations of vortex flows in aircraft and helicopter applications. The articles comprise a wide variety of fundamental investigations and of advanced engineering applications. The book summarizes the state of the art and also communicates recent results of specific flow problems. It addresses the large readership experienced in the field of vortex dynamics.

Physical arguments are developed to show how aerodynamic sound is generated as a result of the movement of vortices, or of vorticity, in an unsteady fluid flow. In a very simple model the aeolian tone is attributed to the dipolelike flow caused by the stretching of vortex rings. There is no net stretching of vortex rings in a free flow, but each moving element of vorticity still causes a local dipole-like flow, so that equal and opposite elements act together to form quadrupoles. Mathematical developments follow. The simple aeolian tone model is shown to be valid for low Strouhal numbers, the general result also incorporating the effect of the fluctuating Bernoulli pressure at the surface of the body. The free flow quadrupole model is shown to be exact, and also to agree with Lighthill's result. Using vorticity as a common basis, the compressible flow is compared to the corresponding incompressible one, the hydrodynamic field and the relationship to classical field theory being discussed. (Author).

V. 1. General concepts and elementary sources -- v. 2. Complex flow-structure interactions.