Part I of the report gives, an account of experiments made with the National Physical Laboratory smoke generator to obtain smoke patterns in the wake of an aerofoil performing a rolling oscillation in a wind stream.nCalculations are given in Part II relating to the smoke patterns produced by a nozzle in uniform motion relative to (a) an infinite row of equally spaced two-dimensional discrete vortices of alternate sign and (b) an infinite two-dimensional vortex sheet with sinusoidal distribution of strength. Comparison with certain of the smoke patterns discussed in Part I suggests that the wake vorticity can be treated very closely as a system of discrete vortices, and this is supported by the consideration that the elements of a continuous vortex sheet would in general be subject to normal induced velocities, which would tend to break the sheet up.
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