AN EXPERIMENTAL STUDY OF DRAG 



REDUCTION BY SUCTION THROUGH 



CIRCUMFERENTIAL SLOTS ON A 



BUOYANTLY-PROPELLED, 



AXI-SYMMETRIC BODY 



Barnes W, McCormick, Jr. 



The Pennsylvania State University 

 University Park, Pennsylvania 



ABSTRACT 



This paper presents the analysis, design, and results of testing per- 

 formed to date on TRI-B, a buoyantly-propelled body incorporating 

 boundary layer control by suction through circumferential slots. This 

 body is designed to maintain a nearly, full-length laminar boundary 

 layer at a length Reynolds number of 39 x 10^. Although the expected 

 performance has not yet been achieved in the field with the free-running 

 body, nearly full-length laminar flow has been measured in wind tunnel 

 tests at lower Reynolds numbers. From the results of an analysis 

 based on the Karman-Pohlhausen method, it is believed that transition 

 is occurring ahead of the first suction slot at the higher Reynolds 

 number. 



INTRODUCTION 



The purpose of this paper is to report on the TRI-B program currently in 

 progress at the Ordnance Research Laboratory. Specifically, the method by 

 which TRI-B, a buoyantly-propelled body with boundary layer control, was de- 

 signed together with an analysis of the experimental results obtained to date 

 will be presented. 



A diagram of TRI-B is shown in Fig. 1. It has an overall length of 93 inches, 

 a diameter of 12.75 inches and displaces 294 lbs. Beginning 6 inches back from 

 the nose and spaced every 2 inches are circumferential slots having a thickness 

 of .007 inches through which the boundary layer is removed. The suction is ac- 

 complished by means of an axial-flow pump driven by a hydraulic motor. The 

 motor is supplied with hydraulic fluid under pressure from a piston driven from 

 an accumulator capable of being pressurized to 5000 psi with nitrogen. 



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