Laboratory experiments on whirlpools

Abstract

Two vertical pipes, placed on the axis of an open circular tank and fitted with trumpet entries of different shapes, were used in turn as overflows. Water was led into the tank in such a way that the stream approaching the trumpet under test possessed tangential velocity, which caused a vortex to appear in and above the trumpet. The relations between head and discharge were determined under various conditions of tangential supply. The formation of a vortex greatly reduced the discharge, the decrease being even more marked with the shallow than with the deep trumpet. At low heads, where the flow was controlled by the weir action of the trumpet crest, the discharge varied with the shape of the crest as well as with the irrotational constant c and the head, therefore (as with purely radial supply) it must be determined by experiment. At high heads with the trumpet flooded, the throat controlled the flow; within certain limits, the discharge was dependent chiefly upon c and the head measured with the throat as datum, and an approximate theory which ignores friction was verified. Two types of instability, ‘surging’ at low heads and ‘spluttering’ at high heads, were examined. Both were due to the collapse and subsequent re-formation of feeble vortices, which caused the discharge to vary with time in a periodic manner.