ABSTRACT 



A comprehensive set of experimental pressure, velocity, and 

 turbulence data are presented across the stern of a three- 

 dimensional model having 3:1 elliptic transverse cross sections. 

 The axisymmetric displacement body concept is extended to three- 

 dimensions and the pressure and velocity data are compared with 

 the predictions of existing three-dimensional theoretical methods. 

 The surface pressures for the displacement body are found to model, 

 satisfactorily, the measured pressure coefficients in all regions 

 except over the aft 7 percent of body length. In this tail region, 

 the boundary layer is much thicker than the cross section dimensions 

 and the theory overpredicts the measured distributions of the mean 

 velocity. Agreement is particularly poor in the inner region of 

 the tail boundary layer, indicating a need to examine the eddy 

 viscosity model currently used in computing the thick stern boundary 

 layer of three-dimensional models. As was found in the axisymmetric 

 case, the measured values of turbulence intensity, eddy viscosity, 

 and mixing-length parameters in the stern region are much smaller 

 than those of a thin boundary layer. 



ADMINISTRATIVE INFORMATION 

 The work described in this report was funded under the David W. Taylor Naval 

 Ship Research and Development Center's Independent Research Program, Program Element 

 61152N, Project Number ZR 000 01, and Work Unit 1542-103. 



INTRODUCTION 

 Many single-screw ship propellers operate inside of thick stern boundary layers. 

 Satisfactory predictions of turbulent boundary-layer characteristics can be made for 

 the forward portions of a body by solving the boundary-layer equations in either 

 integral or differential forms. However, at the ship stern, the thickness of the 

 boundary layer increases rapidly, mainly due to the diminishing cross-sectional area. 

 The thickness of the stern boundary layer usually exceeds the thickness of the body. 



Detailed measurements of the turbulent boundary-layer characteristics in the thick 



*1,2 

 stern boundary layers of axisjnmnetric bodies have been made by Huang et al. in 



order to gain insight into the physics of thick stern boundary layers. These 



measurements have been used to validate the displacement body concept as suggested 



by Preston and Lighthill for solving viscid-inviscid flow interaction and an 



improved turbulence model has been obtained for computing thick axisymmetric boundary 



*A complete listing of references is given on page 105, 



1 



