MEASUREMENTS OF FLOWS OVER AN AXISYMMETRIC BODY WITH VARIOUS APPENDAGES IN A WIND TUNNEL: THE DARPA SUBOFF EXPERIMENTAL PROGRAM

Pressures, velocities, skin friction, and Reynolds stresses were measured in the stern boundary layer region of an axisymmetric body with and without appendages. The data was used to assess and further develop current computational fluid dynamics (CFD) capability for the prediction of flow fields around underwater bodies. The model configurations tested included an axisymmetric hull, a fairwater, one set of four identical stern appendages, and two axisymmetric ring wings. Analyses of measurement uncertainties of all the measured variables are presented. The data was corrected for tunnel effects. Comparison of the measured and computed mean axial velocity and turbulent shear stress profiles demonstrates the important influence of turbulence modelling in CFD prediction of the stern flows. The data illustrates the modifications by various appendages of the basic axisymmetric thick turbulent boundary layers over the stern. The spatial nonuniformity of mean axial velocities and redistribution of the normal and shear stresses are found to be caused by a pair of contrarotating longitudinal vortices generated by each appendage. These are imbedded in the inner stern boundary layer of the hull. The helical rotations of the vortices produce a transverse transport os axial momentum. The high momentum and low turbulence level fluid behind the appendage is pulled inward and the low momentum and high turbulence level fluid to each side of the appendage is pushed upward. The appendage- generated vortices redistribute axial-radial turbulent shear stresses by do not change their circumferential-average values. The imbedded vortices in the stern boundary layer show distinct characteristics of turbulent shear stresses with the mixing length scales governed by the core sizes of the vortices.