The critical phenomenon represented by the presence of local maximum in drag when rearbody slant angle changes was investigated in a series of notch-back type automobile geometries.
The aerodynamic forces were measured for the various shapes each having different back-light rake angle at $Re=8.0×10^5$, $1.0×10^6$ and $1.4×10^6$, based on nominal length. Also surface flow visualization was effected by the oil mixture.
It was found that the critical phenomenon in the notchback type is milder than in the hatch-back type in the following sense: the local maximum in the drag vs. slant angle curve is represented by a much smoother curve.
Surface oil flow visualization revealed that the flow pattern associated with the critical phenomenon is characterized by the reattachment of the separated flow on the boot.
The effect of the forebody on the critical phenomenon was seen to be negligible.
