Experimental investigation of surface roughness effect on a free-flight sphere in a Ludwieg tube

Understanding the aerodynamic coefficients of meteoroid fragments, deorbiting space debris, or launch vehicle stages through atmospheric reentry is essential for ground risk assessments. In high enthalpy flow, surface roughness is a crucial factor affecting the aerodynamic coefficient. In this work, the effect of surface roughness on drag coefficient is investigated experimentally within a Ludwieg tube at a Mach 4 test condition. The test model is a sphere with a 5 mm diameter. Three different types of surface roughness are considered using a pre-heating process. Shadowgraph technique was used to visualize the flow features and model behavior. Based on the acquired high-speed images, the drag coefficients were obtained using an image tracking technique. Results show that the drag coefficient decreases with corresponding increases in surface roughness for the given flow condition, implying the importance of surface roughness effect in ground risk assessments.