An Analysis of Nosetip Boundary Layer Transition Data

A critical analysis is presented of the available wind tunnel data simulating nosetip boundary layer transition on reentry vehicles. It is agreed that transition should depend on surface roughness, surface temperature, and surface curvature. The Reynolds number based on momentum thickness at the transition location (Re sub theta) is used to measure transition, and the surface roughness effect is described by the Reynolds number Rek,k based on roughness height and conditions at the tops of the roughness elements. The wall temperature dependence may be removed by use of the kinematic viscosity in the 'middle' of the boundary layer to compute Re sub theta. The available data suggest a dependence on theta/Rc (Rc = surface radius of curvature), which could be due to centrifugal acceleration or pressure gradient. Accounting for this curvature effect appears to eliminate the need for a separate transition 'onset' criterion. A tentative correlation is presented, and the limitations of the existing data are discussed. Report on Advanced Reentry Aeromechanics.