EFFECTS OF TURBULENCE STIMULATORS ON THE BOUNDARY LAYER AND 

 RESISTANCE OF A SHIP MODEL AS DETECTED BY HOT WIRES 



by 

 John P. Breslin and Morris S. Macovsky 



ABSTRACT 



An experimental study has been made of the effects of various methods of stim- 

 ulating transition from laminar to turbulent flow in the boundary layer of a 25-foot 

 tanker model. A hot-wire velocity instrument has been applied to determine the nature 

 of the flow in the boundary layer. Qualitative and quantitative analyses of the results of 

 the hot-wire surveys with a 1/8-inch rod, a 0.032-inch trip wire and a 7/8-inch fine- 

 grain sand -strip used separately as stimulators are given. The theory of the stability 

 of laminar flow which is briefly reviewed is used for qualitative interpretation of the 

 boundary-layer flow found for the various test conditions. Expected increases in model 

 resistance, because of stimulation as computed from hot-wire data, show good agreement 

 with actual measured increases detected on the towing dynamometer when reasonable 

 corrections are applied to the resistance data. The results of this study show that the 

 hot-wire method is well suited to boundary- layer investigations in water, that the extent 

 of laminar flow on the 25-foot model gives rise to a serious error in model resistance, 

 and that measurable differences in the effects of various stimulators on the boundary- 

 layer flow and on the model resistance can be determined. No conclusive decision can 

 be reached as to the best stimulator, however, as a result of this study. 



Details of the hot-wire theory as applied to measurements in water are given 

 in the appendix. 



INTRODUCTION 



A frictlonal-resistance research program has been initiated at the 

 David Taylor Model Basin 1 to secure a thorough understanding of the frlctional 

 resistance of ship models. To this end, a program of fundamental research was 

 set up and the development of special equipment undertaken. This program pro- 

 vides for the study of boundary-layer phenomena, first under simple conditions 

 on flat plates and later on more complicated forms. During the period in 



Eef erences are listed on page 39 of this report . 



