Neutrally buoyant bubbles used as flow tracers in air

Kerho, Michael F.; Bragg, Michael B.

doi:10.1007/bf00202064

Cited by 29 publications

(30 citation statements)

References 2 publications

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“…Their use for quantitative measurements had been initially attempted with bubbles of several millimeters. The results discouraged follow-ups due to the difficulties in producing HFSB that could accurately follow the flow (Kerho and Bragg 1994). This issue has been resolved through the reduction of the bubble diameter to the sub-millimeter range (about 0.3 mm), and through refining the control of helium and bubble fluid solution (BFS) mass flows to match the bubble density to that of air (Scarano et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Helium-filled soap bubbles tracing fidelity in wall-bounded turbulence

Faleiros

Tuinstra²,

Sciacchitano

et al. 2018

Exp Fluids

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The use of helium-filled soap bubbles (HFSB) as flow tracers for particle image velocimetry (PIV) and particle tracking velocimetry (PTV) to measure the properties of turbulent boundary layers is investigated in the velocity range from 30 to 50 m/s. The experiments correspond to momentum thickness-based Reynolds numbers of 3300 and 5100. A single bubble generator delivers nearly neutrally buoyant HFSB to seed the air flow developing over the flat plate. The HFSB motion analysis is performed by PTV using single-frame multi-exposure recordings. The measurements yield the local velocity and turbulence statistics. Planar two-component-PIV measurements with micron-sized droplets (DEHS) conducted under the same conditions provide reference data for the quantities of interest. In addition, the behavior of air-filled soap bubbles is studied where the effect of non-neutral buoyancy is more pronounced. The mean velocity profiles as well as the turbulent stresses obtained with HFSB are in good agreement with the flow statistics obtained with DEHS particles. The study illustrates that HFSB tracers can be used to determine the mean velocity and the turbulent fluctuations of turbulent boundary layers above a distance of approximately two bubble diameters from the wall. This work broadens the current range of application of HFSB from external aerodynamics of large-scale-PIV experiments towards wall-bounded turbulence.

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Section: Introductionmentioning

confidence: 99%

Helium-filled soap bubbles tracing fidelity in wall-bounded turbulence

Faleiros

Tuinstra²,

Sciacchitano

et al. 2018

Exp Fluids

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“…The uncertainty of measurement using helium-filled soap bubbles has been thoroughly investigated by Kerho and Bragg (1994) at the stagnation region of an airfoil with a chord of 0.5 m at free-stream velocity of 18 m/s. A commercial bubble generator producing HFSB with diameter in the range from 1 to 5 mm was used.…”

mentioning

confidence: 99%

“…The evaluation is conducted in a similar way as in Kerho and Bragg (1994), measuring the bubbles velocity around the stagnation region of a cylinder. Additionally, here, the reference velocity field is not inferred with potential flow theory, but additional PIV measurements with micron-size droplets are carried out.…”

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confidence: 99%

On the use of helium-filled soap bubbles for large-scale tomographic PIV in wind tunnel experiments

et al. 2015

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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 × 12 cm 3 at a rate of 2 kHz. The achieved seeding density of <0.01 ppp enables resolving the Kármán vortices, whereas turbulent substructures cannot be captured.

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“…This means of visualization is described well e.g. in literature (Kerho, 1992). Suitable compounds of such type include soot, sparks or helium bubbles (Kerho, Breagg, 1994).…”

Section: Introductionmentioning

confidence: 98%

“…in literature (Kerho, 1992). Suitable compounds of such type include soot, sparks or helium bubbles (Kerho, Breagg, 1994). This article only focuses on images of air fl ow visualized by helium bubbles.…”

Section: Introductionmentioning

confidence: 99%

Using Neural Networks for Determining Velocity Vectors of Air Flow Visualized by Helium Bubbles

Šťastný¹,

Richter²,

Šťastný³

2014

Acta Univ. Agric. Silvic. Mendelianae Brun.

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One of the important characteristics of air fl ow is the velocity of fl ow. To determine the speed, in addition to other methods, we also use the helium bubbles seeding visualization method, when bubbles are injected into the air stream so that the air fl ow is obvious to the eye. If a video of such fl ow is taken, it is possible to determine velocity vectors in a pair of consecutive frames of this video footage, derived from the change in position of individual bubbles. This article describes a method of monitoring the bubbles in consecutive video frames. During this process, helium bubbles are detected in the fi rst image of the pair, either by a fi rmly defi ned procedure, or with the use of a neural network. For detected bubbles, the velocity vectors are determined according to the way in which they move, therefore, according to their location in the following frame. Another neural network then determines the velocity vector at any point of image, which will be implemented in the construction of vector maps for the fi rst image. A vector map is used for comprehensive evaluation of air fl ow and thus, plays an important role in the development of ventilation and air conditioning systems.

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Neutrally buoyant bubbles used as flow tracers in air

Cited by 29 publications

References 2 publications

Helium-filled soap bubbles tracing fidelity in wall-bounded turbulence

Helium-filled soap bubbles tracing fidelity in wall-bounded turbulence

On the use of helium-filled soap bubbles for large-scale tomographic PIV in wind tunnel experiments

Using Neural Networks for Determining Velocity Vectors of Air Flow Visualized by Helium Bubbles

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