University of Waterloo, Waterloo, Ontario: 16mm.
"The unsteady fluid motion in a rotating impeller with respect to a rotating reference frame is studied. The photographic information is obtained by adapting the Hydrogen Bubble flow visualization technique for higher velocities and rotating systems. This high speed movie shows the characteristic flow patterns associated with the passage flow stall and recovery for a shrouded and unshrouded impeller passage at the inlet and discharge sections. At part capacity the passage flow breaks down and some of the pump passages act as turbine passages. The motion is a cyclic pulsation. The point of boundary layer separation in the passage (and, therefore, the mechanism of rotating stall) depends strongly on the impeller geometry (i.e., shrouded or unshrouded impeller) and shows characteristic flow patterns, different at the inlet and discharge sections of the passage. At zero flow a stationary vortex builds up at the passage discharge side due to the strong momentum exchange between diffusor and impeller."