Boundary-Layer Characteristics and Effects of Threadlike Roughness for a High-Slenderness Projectile

The aerodynamic properties of high-slenderness finned projectiles with and without a threadlike roughness element on the shaft were evaluated. The alteration of the aerodynamic coefficients of the longitudinal motion due to the surface roughness were investigated by means of strain gauge balance and free-oscillation measurements in a supersonic blowdown wind tunnel. The test conditions cover a Mach number range from 2.5 to 4.1 at diameter-based Reynolds numbers from [Formula: see text] to [Formula: see text]. The forebody axial force was found to be significantly increased by the thread element with the deviations compared to the smooth-shaft case growing overproportionately with increasing angle of attack. Whereas a minor influence by the thread element was observed for the normal force, the pitching moment is significantly altered by the thread element. Flow visualizations by single frame as well as videographic schlieren setups gave insights into the underlying flow physics. The overall flow topology, the boundary-layer thickness, the laminar-turbulent of the boundary layer, the separation of the flow at high angles of attack, and the interaction between the boundary layer and the individual thread elements were captured.