The moiré technique can be applied to problems of fields and flows. Thus in hydrodynamics the flow of liquid from a source may be represented by a figure of radiating lines; the greater the source strength, the smaller will be the angular openings. As no positive or negative radial direction is indicated, the figure can also be used to represent a sink. Two such figures when superposed give a moiré pattern, which is the resultant flow of liquid for a source near a sink. This is also the field for an electric dipole, a positive charge close to a negative charge. When a simple parallel-line grating is superposed on a radial figure, one obtains the flow pattern for a source of liquid in a moving stream. This result, which is ordinarily difficult to calculate, is readily obtained and in graphic form by the moiré method.
The vortex, or circular motion, of fluids is represented by circles in which the spacing is greater as one goes out from the center. Superposition of two such figures gives the resulting flow for two vortex centers of opposite sense. The moiré pattern also represents the lines of the same voltage (the equipotentials) looking down the ends of two wires which are oppositely charged. It should be noticed that the pattern is turned 90° from that for the radial figures. By superposing this circular figure with other figures, one can obtain the flow of air about an airplane wing, for example.
The vortex, or circular motion, of fluids is represented by circles in which the spacing is greater as one goes out from the center. Superposition of two such figures gives the resulting flow for two vortex centers of opposite sense. The moiré pattern also represents the lines of the same voltage (the equipotentials) looking down the ends of two wires which are oppositely charged. It should be noticed that the pattern is turned 90° from that for the radial figures. By superposing this circular figure with other figures, one can obtain the flow of air about an airplane wing, for example.