Wake Instability and Frequency Selection of the von Karman Vortex Shedding.

In order to better understand the von Kármán vortex shedding on the basis of the concept of absolute instability, the vortex shedding from a blunt-ended flat-plate is examined experimentally through controlling the wake development. The stability analysis is also made for the velocity distributions in the near wake region to obtain their local instability characteristics. When the vortex shedding is controlled by another flat-plate in the wake, the shedding frequency is remarkedly changed. Such change in frequency is found to be closely related to the change in the absolute instability characteristics of the wake velocity distributions immediately behind the plate base.