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Show 11 and 17 percent for roof angles of 30°, 40°, and 50°, respectively. Additional traverses in the downwind direction indicated that the maximum increase did not occur exactly at the trailing edge of the roof but approximately .3 m ( full scale) downwind from the trailing edge. The maximum speed could be as much as 30 percent greater than the mean speed at this point, although the increase was maintained only for a very short distance downwind. This relatively large increase in speed at the larger angles of inclination ( 30°, 40°, and 50°) js a probable explanation for the effectiveness of jet roofs which are inclined at steep angles on correspondingly steep lee slopes. The increased speed in this case does not propagate very far in the downwind direction, but the steep angle of the lee slope makes an extended downwind effect unnecessary. Although the model studies were by no means comprehensive, the preliminary results do appear to be promising, and it is expected that more information on possible design trends could be gained from further model i nvestigat ion. Ridgeline Wind Action. Using the principles learned in the full scale and laboratory model experiments, it is possible to gain some understanding of the jet roof fluid mechanics on a mountain ridge. For greatest wind speed increases, the inclination angle should be between I0° and 20° from the surface wind plane in the downwind direction. Considering the windward plane only, theoretically the most efficient inclination angle would be 20 degrees minus the windward slope angle, assuming that the airflow is parallel to the slope. However, since redirecting the wind is an important function of the jet roof, it is always practical to incline the structure in the lee slope direction. A good rule of thumb is to incline it at approximately the lee slope angle. |