Foam is a compressible medium which can have a density corresponding to that of a liquid and a compressibility corresponding to that of a gas. As a result, compressibility effects such as choked flow can be obtained at relatively low velocities. It is not possible to make “Mach number tables” for foam—as it is for gas—since the properties depend on stagnation foam density as well as Mach number. The equations for the flow of foam are nondimensionalized and presented in a form such that universal curves can be produced. This simplification facilitates the manipulation of the equations; for example, the test for a sonic throat follows easily from the formulation, and an approximation is found that applies near the throat. The procedure for calculating the characteristics of one-dimensional duct flow is outlined, and the charts necessary to carry out the graphical computation are shown in this paper.

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