Global Flow Diagnostics of a Space Orbiter: Skin Friction, Surface Pressure and Velocity

This paper describes the extraction of global high-resolution skin friction, surface pressure, and flow velocity fields on a space orbiter. First, skin friction topological data is obtained using the global luminescent oil-film (GLOF) skin friction meter. This technique uses the thin oil-film equation to establish a relation between skin friction and the thickness and luminescent intensity of a thin oil-film doped with a luminescent dye. Next, surface pressure distributions are reconstructed from skin friction fields by using the relation between surface pressure and skin friction given by the Navier-Stokes (NS) equations. Finally, global flow velocity data is extracted using optical flow velocimetry (OFV). Developed using the physics based optical flow equation, this technique extracts global velocity data from a sequence of images with continuous patterns such as laser-induced smoke visualization. To provide a more complete understanding of the working principles behind the global flow diagnostics, a detailed description of each of the techniques used is presented. Skin friction, surface pressure, and flow velocity measurements were performed on a generic space orbiter vehicle at a freestream velocity of 35 m/s (Mach 0.1) corresponding to a length-based Reynolds number of ReL = 4.26 × 105 and four angle of attacks (AoAs) of 0°, 10°, 20°, and 30°. Additionally, coefficient of lift, CL, coefficient of drag, CD, and lift-to-drag ratio, L/D, measurements were performed. The results obtained are evaluated.