Effect of internal geometry and orientation on the performance of a helium-filled soap bubble nozzle

Abstract

Various design considerations for helium-filled soap bubble generators are investigated. These include the effects of modifying internal nozzle geometry and nozzle operating orientation on nozzle performance, as well as the tracing fidelity of the bubbles produced by a multi-nozzle system and the impact of placing a full-scale generator in the settling chamber of a wind tunnel. Modifications to internal nozzle geometry are found to directly impact the nozzle production regimes, and some evidence is provided to suggest that operating orientation does the same. The mean time responses are found to obey a previously defined theoretical relationship (Engler Faleiros et al. 2019, Exp Fluids), and the standard deviations of the time response distributions indicate that 95% of the bubbles produced by the system will accurately track velocity fluctuations with a time scale of 3 ms or greater when the bubbles are neutrally buoyant on average. Placing a full-scale generator in the settling chamber of a wind tunnel is found to increase the maximum freestream deficit by up to 1.2% and the freestream turbulence intensity by at most 0.3% for freestream velocities between 6 and 30 m/s.