An experimental study on plunging cylinders

Abstract

This paper is an experimental study on plunging cylinders. Four nosecone shapes, cylindrical, conical, parabolic and power series 0.5 with a variation of material type, aluminium and steel were studied. There are two parts to this experiment, high-speed imaging and particle image velocimetry. High-speed camera captured the projectiles traversing from air to water. The images were calibrated, tracked, and the extracted data were filtered and analysed. Particle image velocimetry were utilized for flow visualization. Comparisons between nosecone shape and the projectile mass will be discussed the output data of velocity, impact acceleration, coefficient of drag, cavitation growth and flow visualization. It was found that cylindrical projectile has the biggest change in acceleration when traversing between air and water, resulting in the biggest drag coefficient. From PIV data, conical projectile displaces water at the smallest magnitude. The parabolic and power series projectiles have the smallest impact forces when the projectile mass is increased. Increase in projectile mass resulted in a decrease of coefficient of drag. Cavitation growth influences the performance of the projectile, projectile with surface seal decelerates rapidly, whereas a projectile with deep seal tends to accelerate continuously. Finally, increase in flow activity around a projectile reduces the acceleration performance i.e. causes energy loss resulting in deceleration. Suggestions for improvement and future research were also provided.