In an earlier note Case reported direct measurements of entrainment on a rotating disc. More comprehensive measurements, made subsequently to those of Case and using essentially the same technique, are reported here. Two different sizes of drum were used in the present investigation, the flow within the drum in each case being smoothed by the use of a honeycomb and screens as well as a baffle at entry (see Fig. 1).

The entrainment was also deduced from yawmeter and total pressure traverses through the boundary layer on the disc in free air, the integrated crossflow component of the velocity distribution through the layer evidently representing the entrainment up to the radius at which the traverses were performed. A typical measured crossflow profile is shown in Fig. 2.