An attempt is made to clearly distingxish the effect of a groove shape on
the aerodynamic characteristics of a circular cylinder. The grooves are
used as a passive control for the boundary layer separation. Grooves of
different cross section shapes are made on the cylinder surface to
investigate the effect of a regular surface configuration and to elucidate
the flow structure in the wake region where the effect ofgrooves is
existed. The results show that the grooves greatly affect the location of
the separation point in which a shift of the flow regime to lower Reynolds
number is found. The subcritical, critical and supercritical regimes can
easily identified from flow measurements. It is found that the critical
Reynolds number for tested grooved cylinders is 5x10~ which are below
the subcritical Reynolds number of a smooth cylinder. The critical
Reynolds number for a smooth cylinder is 3x10'. The main features of the
boundary layer development are quit the same as that of the smooth
cylinder. The boundary layer thckness and shape factor are large for
grooved cylinders compared to that of the smooth cylinders and these
results are in good agreement with previous available data.