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Pressure-speed correlation

The test measurements were analysed in order to find some general relationships useful for parametric design analyses. No correlation is found between mean values and wind speed on the mirror. The reason is that we have in many cases large differences in mean pressure on the four pressure taps and also in some instances a reversed flow on the mirror, whereby the mirror upper surface is actually under a mean negative pressure.

On the contrary a correlation between and wind speed is well established and is independent of the wind direction. Recalling that is referred to the external reference speed :

we introduce a similar coefficient referred to the wind speed U measured on the mirror:


obtaining the relationship


Fig. gif is a scatter plot of this relationship. The correlation is independent of the azimuth angle and of the venting configuration of the enclosure. The coefficient depends only on the zenith angle:

, for zenith angle , for zenith angle


Although it cannot be generalized to other types of enclosures, this result suggests that simple parameterisations between speed measurements and pressure fluctuations should be looked for in the study of a new enclosure. Since the ratio is a parameter that can be adjusted by acting on the ventilation devices of the enclosure (louvers, windscreen), a relationship of the type (gif) will be particularly useful for parametric design analyses as well as for operational simulations of the use of the enclosure venting devices.

Lorenzo Zago,, Sun Feb 26 22:57:31 GMT+0100 1995