Viscous drag reduction of a nose body

Abstract

The convex curvature concept of viscous drag reduction has been applied to an axisymmetric nose-body combination. The work is described in two parts. A modified mixing-length formulation is first qualified in several complex turbulent boundary layers that are primarily curved. This is then used to design an axisymmetric nose that incorporates several recently proposed concepts of viscous drag reduction. Primarily, application is made of the fact that compared to a flat surface, the effect of streamwise convex curvature is to reduce skin friction, and the level remains lower even after the curvature is removed. A parametric study has been conducted to incorporate the conflicting requirements in a nose, viz., the application of the drag reduction concepts at an optimized level while causing no separation. The axial distribution of the cross-sectional area ratio is found to be critical to separation. This required the drag reduction concepts to be implemented over several short fetches of curvature instead of a single long fetch. A novel three-stage nose has been designed that does not separate while incorporating the drag reduction concepts. This has been compared with two equivalent nose bodies.