An experimental determination of the effect of the axisymmetric turbulent wake on the pressure distribution on a sphere

A study of the effect of the turbulent wake of a water drop on the motion of a smaller droplet is essential in order to gain an understanding of the behavior associated with the collision coalescence phenomena. The use of spheres of macroscopic size proves to be a valuable method in observing these effects. This experimental investigation centers on (1) a check on the validity of the instrumented sphere as a device to measure normal static pressure, and (2) the study of the effect of the turbulent wake of the test model sphere upon the instrumented sphere. Measurements were made in a subsonic wind tunnel with a test section of 20 x 20 inch cross section and 42 inches length. Mean velocity profiles indicate that the boundary layer is thin and turbulence measurements show the tunnel to have low turbulence. The experimental method is proven valid by measuring the pressure distribution on the sphere surface with the sphere in the free stream and comparing the results to those of other experimentalists and to a viscous analytical solution. Normal pressure is then measured using the instrumented sphere in the near wake of the test model at various locations. The resultant forces are calculated using graphical type integration The results show the axial (Z direction) component of force to range from a lower value at the wake centerline to a value equal to that of the free stream drag as the sphere is traversed out of the wake. This gradient tends to become smaller the further downstream the measurements are taken. The trends of the axial (Z direction) component of force are similar to those of the mean velocity profile in the wake of the test model. The transverse force components (X and Y directions) are zero on the centerline and increase to a maximum just to one side of the centerline and then diminish as the wake boundary is crossed. As with the axial (Z direction) component, the transverse components (X and Y directions) are less amplified the further downstream the measurements are taken --Abstract, pages ii-iii