39 



The use of a multichannel oscillograph to record a number of signals 

 simultaneously imposed one other limitation on the frequencies recorded. It 

 was necessary to limit the amplification to that level where legibility of a 

 single trace was not obscured by the other traces. Hence in view of this fact, 

 signals of high frequencies but low amplitude were not sufficiently amplified 

 and were not discernible. 



In spite of these restrictions, subsequent test records have shown 

 velocity fluctuations in the order of 300 cps. Although it is assumed that 

 higher frequencies were present in the turbulent boundary layers investigated, 

 they were probably not recorded as a result of the amplification and galva- 

 nometer limitations. 



REFERENCES 



1 . Hydrodynamics Memorandum to the Director, DTMB, entitled "Develop- 

 ment of an Experimental Technique for Detecting Transition from Laminar to 

 Turbulent Flow in a Boundary Layer," All /Resistance (l8:LL:fct) dated 11 Aug- 

 ust 1947. 



2. Schubauer, G.B. and Klebanoff, P.S., "Theory and Application of Hot 

 Wire Instruments in the Investigation of Turbulent Boundary Layers," NACA 

 ACR No. 5K27, March 1946. 



3. Schubauer, G.B. and Skramstad, H.K., "Laminar Boundary Layer Oscil- 

 lations and Transition on a Flat Plate," National Bureau of Standards Journal 

 of Research, Vol. 38, February 1947. 



4. Lin, C.C., "On the Stability of Two-Dimensional Parallel Flows," 

 Quart. Applied Math, Vol. 2, No. 3, July 1945, pp 117 - 142; Vol. 3, No. 3, 

 October 1945, pp. 21 8 - 2}4; Vol. 3, No. 4, January 1946, pp. 277 - 301. 



5. Schlichting, H., Lecture Series "Boundary Layer Theory," Part II - 

 Turbulent Flows, NACA Tech. Memo No. 121 8, Washington, D.C., April 1949, p. 

 33- 



6. Pohlhausen, K , "Zur Naherungsweisen Integration der Differential- 

 gleichung der laminaren Grenschicht, " Zeit. f. ang, Math", u. Mech., Vol. 1 

 (1921) No. 4, p. 252. 



7. Allan, J.F. and Conn, J.F.C., "Effect of Laminar Flow on Ship 

 Models," a paper presented at the Autumn Meeting of Institution of Naval 

 Architects at Copenhagen, 1 9^+9 . 



