Isotropic turbulence was caused in a wind tunnel, the working section of which was 12 feet long, and of cross section approximately 20 inch×20 inch. The grid consisted of wooden dowells, 0·5 inch. in diameter regularly spaced with a mesh of 1·5 inch, inserted where the working section begins. Decay and correlation of the turbulence were measured by means of a hot-wire, anemometer. Wollaston wire being used. This was a platinum wire, 0·0005 in. in diameter coated with silver. The silver was etched off in such a way that the length of the platinum wire became approximately 2mm. The experiments were made at three different speeds; namely, 29·8, 38·0 and 53·5 ft per sec.
The results are summarized as follows:
(1) Decay of the intensity of the turbulence was practically independent of wind velocity and was proportional to (x/M)
-5a.
(2) Scale of the turbulence increased as distance downstream of the grid increased and was proportional to (x/M)
1-5a.
(3) At a fixed point in the turbulence stream, the scale of the turbulence was approximately independent of the mean wind velocity.
(4) The correlation curves indicated that their shapes were preserved with the exception of very small values of the distance r, at which the experimental points were unreliable because of interference of the hot-wires.
(5) u'λλ
2/νL was constant.
(6) dL/dt was directly proportional to √uu
2.
(7) From the theoretical point of view, AB=5.
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