Abstract
Stability of horizontal and periodic vortices formed in compound open channels is studied in terms of shear instability and Karman's vortex street stability. It was found that two arrays of vortex street become very stable when the periods predicted from both instabilities agree with each other. 3-D structure of the organized vortices was observed by employing a conditional sampling technique, in which 2-D laser-Doppler anemometer and hotfilm anemometer were used in tandem. The velocity distribution obtained by spatial averaging for one wave length of vortex shows a typical secondary flow usually seen at the corner of compound channels.
