Measurement in small wind tunnels of wind speeds for gravel scour and blowoff from rooftops

Abstract

This paper examines the validity of using small scale wind tunnel tests to predict wind speeds at which gravel or crushed stone will scour or blow off flat rooftops. Tests carried out at 1:10 scale in a 9 × 9 m tunnel were repeated at reduced scale in a small tunnel. Comparison of the results showed that the small scale tests were subject to significant Reynolds number effects. These were mainly associated with the flow/stone interaction process and are shown to be very similar to the Reynolds number effects which influence the shear velocity at which saltation is initiated by two-dimensional flow over long beds of particle. Extensive data exist for the latter process and these are used as the basis of a correction factor which can be applied to small scale scour and blowoff results. It is concluded that small scale testing can give satisfactory predictions, provided that the correction factor is applied. Model stone sizes down to about 0.1 mm can be used.