Experimental simulation of a density-driven downburst translating within a turbulent boundary layer
Abstract
Downburst outflows emerging from thunderstorm producing clouds are contained within the atmosphere where the outflow interacts with the preexisting atmospheric boundary layer (ABL). This novel study employs a realistic approach for experimental simulation of downbursts by translating the downburst source within a scaled ABL within a hydraulic flume system that produces open channel flow. The density-driven model approach is used, involving an iris operated cylinder release mechanism translating inside the ABL generated over a restrictive fetch using passive turbulence generating devices at model scales of 1:5500 and 1:10,000. The velocity vector fields across a vertical plane revealed asymmetrical outflows generated from the complex interaction of the downburst outflow with the ABL. Also, peak velocities as high as 26.2 m/s at full-scale were observed at the downstream side of the outflow after touchdown. A lower cylinder release height and higher ABL flow speed generated larger magnitudes of peak velocity at the downstream end of the outflow.