caa a22 4500 606198946 CHVBK 20210128100936.0 cr unu---uuuuu 210128e20150201xx s 000 0 eng 10.1007/s00348-015-1909-7 doi (NATIONALLICENCE)springer-10.1007/s00348-015-1909-7 On the use of helium-filled soap bubbles for large-scale tomographic PIV in wind tunnel experiments [Elektronische Daten] [Fulvio Scarano, Sina Ghaemi, Giuseppe Caridi, Johannes Bosbach, Uwe Dierksheide, Andrea Sciacchitano] The flow-tracing fidelity of sub-millimetre diameter helium-filled soap bubbles (HFSB) for low-speed aerodynamics is studied. The main interest of using HFSB in relation to micron-size droplets is the large amount of scattered light, enabling larger-scale three-dimensional experiments by tomographic PIV. The assessment of aerodynamic behaviour closely follows the method proposed in the early work of Kerho and Bragg (Exp Fluids 50:929-948, 1994) who evaluated the tracer trajectories around the stagnation region at the leading edge of an airfoil. The conclusions of the latter investigation differ from the present work, which concludes sub-millimetre HFSB do represent a valid alternative for quantitative velocimetry in wind tunnel aerodynamic experiments. The flow stagnating ahead of a circular cylinder of 25mm diameter is considered at speeds up to 30m/s. The tracers are injected in the free-stream and high-speed PIV, and PTV are used to obtain the velocity field distribution. A qualitative assessment based on streamlines is followed by acceleration and slip velocity measurements using PIV experiments with fog droplets as a term of reference. The tracing fidelity is controlled by the flow rates of helium, liquid soap and air in HFSB production. A characteristic time response, defined as the ratio of slip velocity and the fluid acceleration, is obtained. The feasibility of performing time-resolved tomographic PIV measurements over large volumes in aerodynamic wind tunnels is also studied. The flow past a 5-cm-diameter cylinder is measured over a volume of 20×20×12cm3 at a rate of 2kHz. The achieved seeding density of <0.01ppp enables resolving the Kármán vortices, whereas turbulent sub-structures cannot be captured. The Author(s), 2015 Scarano Fulvio Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut Ghaemi Sina Mechanical Engineering Department, University of Alberta, Edmonton, AB, Canada aut Caridi Giuseppe Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut Bosbach Johannes Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Göttingen, Germany aut Dierksheide Uwe LaVision GmbH, Göttingen, Germany aut Sciacchitano Andrea Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-12 0723-4864 56:2<1 2015 56 348 https://doi.org/10.1007/s00348-015-1909-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-1909-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Scarano Fulvio Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut NATIONALLICENCE 700 1- Ghaemi Sina Mechanical Engineering Department, University of Alberta, Edmonton, AB, Canada aut NATIONALLICENCE 700 1- Caridi Giuseppe Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut NATIONALLICENCE 700 1- Bosbach Johannes Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Göttingen, Germany aut NATIONALLICENCE 700 1- Dierksheide Uwe LaVision GmbH, Göttingen, Germany aut NATIONALLICENCE 700 1- Sciacchitano Andrea Aerospace Engineering Department, Delft University of Technology, Delft, The Netherlands aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-12 0723-4864 56:2<1 2015 56 348