A novel wind tunnel testing method for debris flight in turbulent winds

Abstract

Understanding the flight characteristics of windborne debris is crucial for risk mitigation. To physically capture the flight trajectories of small-size windborne debris (using, for example, high-speed cameras), boundary-layer wind tunnel tests need to be conducted at a relatively large geometric scale. However, under a large geometric scale the deficiencies in low-frequency turbulence are significant for conventional wind tunnels with passive turbulence generation. The low-frequency turbulence deficit can lead to a remarkable underestimation in the variation of debris flight trajectories, which compromises the scalability of wind tunnel tests. Although active devices can be used to physically introduce low-frequency turbulence, they are typically not accessible for many researchers and facilities. To this end, one alternative approach based on the “quasi-steady assumption” is introduced in this study to investigate debris flight in turbulent winds without active turbulence generation. In this “quasi-steady approach”, low-frequency turbulence is first considered by physically conducting conventional wind tunnel tests under multiple mean wind speeds and passively generated high-frequency turbulence. The results are then numerically post-processed according to the statistics of the full turbulence spectrum to correct the low-frequency deficit impact on debris flight. In this study, the proposed “quasi-steady approach” and baseline “unsteady approach” (with actively generated full-spectrum turbulence) are compared both numerically and experimentally. The results suggest good agreement of the two approaches, and potential factors accounting for the discrepancies are discussed to guide future investigations.