UiJ 



Amplifier 

 TMB Type 3-A 



Consolidated 

 14 - Channel 

 Oscillograph 



Figure 2a - Circuit Used for Boundary-Layer Survey 



Figure 2b - Hot Wire Probe Showii 

 Plastic Handling Piece 



Figure 2 



many as 14 hot wires may be recorded simultaneously by this oscillograph but 

 in this test only U channels at most were used at one time . 



For this qualitative application of hot wires, neither calibration 

 nor compensation for thermal-lag of the wires was attempted. In spite of this, 

 a given wire reproduced relatively the same oscillogram for the same con- 

 ditions, and repeated runs reproduced the same over-all boundary-layer "pic- 

 tures" even after many hours of testing with the same wires. The problems of 

 calibration and of compensation for thermal lag, as they arise in applying 

 this technique to water measurements, are described in the appendix of this 

 report . 



For maximum sensitivity a wire must be placed perpendicular to the 

 mean velocity of the flow. To find this direction at each of the J>6 positions 

 at which hot wires were to be installed, a single tube was inserted at each 

 location and a lines-of-flow test was run at a mean speed of 1.75 knots. Fig- 

 ure 3 shows photographs of the result. The direction of the flow having been 

 determined at each location, a line through the center of the tube was drawn 

 perpendicular to the direction of flow. The second tube or socket for mount- 

 ing the probe was located along this line, see Figure 4. A sketch showing how 

 the wire is located with respect to the surface and a computed boundary-layer 

 thickness is given in Figure 5- (The boundary-layer thickness is calculated 

 from Equation [20], page 32.) The general arrangement of the probes may be 

 seen in the photograph of Figure 6. The location of the hot wires and the 

 angles of the mean flow at each wire are given in Table 1 . 



