Development and Validation of Helium-Filled Soap Bubble System for Time-Resolved Velocimetry

Traditional tracer particles used for Particle Image Velocimetry (PIV) imposes a limitation during time-resolved PIV measurements, where the laser pulse energy is nominally low. One solution to overcome this limitation is the use of neutrally buoyant helium-filled soap bubbles (HFSBs) as tracer particles, which have a much higher light scattering intensity than traditional particles. To this end, a HFSB system was designed and fabricated at Auburn University to enable time-resolved velocity field measurements. An orifice type nozzle was designed similar to previous investigations and was fabricated using a metal 3D printer with sufficient spatial resolution. The HFSB system was characterized by measuring the bubble diameter and production rates as a function of the nozzle design parameters. The HFSB system will be used to measure velocity field data for canonical flows, as a validation of the tracing fidelity of HFSBs, when compared to traditional particles. The system will be optimized to ensure appropriate time response characteristics of the tracer particles for such canonical flows with the eventual goal of applying it to flows commonly associated with rotorcraft.