The effect of critical Reynolds number and zonal characteristics on asymmetric vortices at forebody

An experimental study with pressure measurement and oil-flow visualization was conducted about evolution of the pressure and side force behaviors with variety of Reynolds number over an ogive-cylinder model in a range of Reynolds number from 0.13×10⁶ to 0.81×10⁶ at 50 degree angle of attack. The results showed that the transitional separation with separation bubbles first occurred on the lower vortex side with increasing Reynolds number into lower critical region, but the boundary layer on the higher vortex side remained the laminar separation. Comparing with that in subcritical region, the asymmetry of the flow is enlarged and the side force is larger. With increasing Reynolds number into upper critical region, the transitional separation also occurred on the higher vortex side and the asymmetric flow gradually became symmetric, the pressure distribution presented a symmetrically flat shape and the side force became much smaller, even approached to zero. So the initial critical regime and critical regime was found in the critical Reynolds number region based on the different separation pattern that is L/Tr and Tr/Tr on both sides of the slender body by using the criterion of pressure difference between separation point and minimum pressure point. Finally, the phenomenon of different separation types existing along the body axis was discussed based on the criterion.