FLUID DYNAMIC FORCES ON A SPHERE SUBMERGED IN TURBULENT BOUNDARY LAYER

Abstract

Knowledge of drag and lift forces on a sphere kept in gradient flow near boundary assumes importance in a variety of engineering problems. While there is some information on these forces for a sphere kept on a boundary roughened with similar spheres, very little work has been done with smooth boundary especially at high Reynolds number flow. Even in the case of rough boundary there is no information on lift force based on direct measurements at high Reynolds number flow. This thesis presents an experimental study concerning the foregoing aspects at high Reynolds number flow, on a stationary sphere placed in a boundary layer type gradient flow. Experiments were carried out in a subsonic wind tunnel of size 510 mm x 510 mm with smooth and rough boun dary conditions. Aparallel-link-force-dynamometer using permeance type displacement transducers, was designed to simultaneously measure the drag and lift forces independently. Mean and fluctuating components of drag and lift were collect ed for different sizes of test spheres kept near and away from the boundary. The variation of the drag and 31ft coefficients with the relevant parameters has been presented graphically. The possibility of occurrence of negative lift even at high Reynolds numbers has been demonstrated and an attempt has been made to identify a criterion for its occurrence.