Equal‐energy streamlines

Energy streamlines show the direction of energy flow in a sound field: The intensity vector at any point is tangential to the streamline passing through that point. In earlier work, a procedure for computing energy streamlines was described [J. Acoust. Soc. Am. 78, 758–762 (1985)], but it did not give equally spaced streamlines. The latter have certain advantages, and a method for computing them is presented here. It is shown that in sound fields which vary in only two space dimensions, a scalar stream function exists, the contours of which are the energy streamlines. The stream function is obtained from the intensity function (or values) by an integration procedure. Examples of equally spaced streamlines are given for the point‐driven, fluid‐loaded plate, and for the baffled rigid piston.