. Effects of turbulence stimulators on the boundary layer and resistance of a ship model as detected by hot wires . 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, a
. Effects of turbulence stimulators on the boundary layer and resistance of a ship model as detected by hot wires . 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 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.
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