Analysis of Turbulent Boundary-Layer over Rough Surfaces with Application to Projectile Aerodynamics
Abstract
A new correlation of the roughness density effect on the intercept of the law of the wall and the equivalent sand roughness, has been developed. The data base used includes corrected results of Schlichting's rough channel experiment and those of twelve other studies. The roughness density parameter used is a product of the reference surface to the total frontal area ratio and a shape factor. For two dimensional roughness, the new parameter correlates data for circular wires with that of square bars. For three-dimensional roughnesses, it correlates results from all four types of roughness studied by Schlichting. The effect of three-dimensional roughness is a little smaller than that of two- dimensional roughness, having the same density parameter. A component build-up engineering analysis has been used to estimate the additional axial-force, due to grooves and threads, of projectiles. Comparison of this prediction technique and wind-tunnel data shows good agreement. Because the groove roughness, in the case considered here, is beyond the range of applicability of the new correlation, existing data are used to estimate an equivalent sand roughness. A turbulence model, based on that of Healzer and the equivalent sand roughness concept has been implemented in the Schiff and Steger PNS code. In order to numerically evaluate the conditions over a rough surface, a transition region between smooth and rough surfaces is introduced. This transition region allows the effect of the rough surface conditions to propagate into this viscous flow region in a realistic way. The predicted smooth body axial force coefficient, excluding the base drag, is five percent smaller than that measured in a wind tunnel test.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1988
- Accession Number
- ADA206747
Entities
People
- Asher Sigal
- James E. Danberg
Organizations
- Ballistic Research Laboratory