Investigations into incompressible steady base flows

Abstract

The turbulent incompressible two-dimensional base flow was investigated in order to get a closer understanding of the laws which determine the base pressure and pressure drag of the body. To this end, the ratio of the turbulent shear stress to the kinetic energy of the turbulent velocity fluctuations, i.e. the parameter α, was predicted for various wedges, and it was detected that in an actual flow α depends solely on the wedge angle and not on the base pressure and pressure drag of the body. The parameter α increases as the wedge angle increases and is for the wedge angle φ = 180 ° (flat plate perpendicular to the freestream) about 1.89 times the value which it has for the wedge angle φ = 0 ° (flow past a backward facing step). The shear stress on the dividing streamline, i.e. ρ u ′ v ′ ¯ , increases even faster with the wedge angle than α, and is for φ = 180 ° about 2.60 times the value which is valid for φ = 0 ° . It was also observed that the length of the dead-air region doesn't depend only on the wedge angle, but also on the ratio of the turbulent shear stress to the kinetic energy of the turbulent velocity fluctuations. Finally, a new method was developed for base pressure prediction of blunt bodies. When the method was applied on wedges, the theoretical values agreed well with the experimental data.