Abstract
Research has been performed to determine the accuracy of neutrally buoyant and near-neutrally-buoyant bubbles used as flow tracers in an incompressible potential flowfield. Experimental and computational results are presented to evaluate the quantitative accuracy of neutrally buoyant bubbles using a commercially available helium bubble generation system. A two-dimensional experiment was conducted to determine actual bubble trajectories in the stagnation region of a NACA 0012 airfoil at 0° angle of attack. A computational scheme evaluating the equation of motion for a single bubble was also used to determine the factors which affect a bubble's trajectory. The theoretical and computational analysis have shown that neutrally buoyant bubbles will trace complex flow patterns faithfully in the flowfield of interest. Experimental analysis revealed that the use of bubbles generated by the commercially available system to trace flow patterns should be limited to qualitative measurements unless care is taken to ensure neutral buoyancy.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Abbreviations
- a c :
-
centripetal acceleration
- c :
-
model chord
- c D :
-
bubble drag coefficient
- D :
-
bubble diameter
- g :
-
acceleration due to gravity
- g v :
-
acceleration due to gravity vector
- h :
-
trajectory deviation normalization parameter
- K :
-
nondimensional inertia parameter, \(\sigma D^2 U_\infty /18c\mu \)
- m f :
-
mass of fluid
- m p :
-
mass of bubble
- p :
-
static pressure
- r :
-
radial distance, bubble radius
- R :
-
gas constant
- Re :
-
free-stream Reynolds number, \(\rho cU_\infty /\mu \)
- Re p :
-
bubble slip Reynolds number, \((\rho DU_\infty /\mu )|v_p - v_f |\)
- S :
-
cross-sectional area of sphere
- T :
-
temperature
- t :
-
time
- u :
-
streamwise velocity component
- U ∞ :
-
free-stream velocity
- v f :
-
fluid velocity vector
- V p :
-
bubble velocity vector
- x p :
-
bubble position vector
- y b :
-
bubble trajectory y/c
- y s :
-
streamline y/c
- α :
-
model angle of attack
- γ :
-
bubble solution surface tension
- Γ :
-
potential vortex strength
- ϱ bfs :
-
bubble solution density
- ϱ :
-
fluid density
- σ :
-
bubble density
- Γ :
-
bubble wall thickness
- μ :
-
fluid viscosity
References
Anonymous (1988) SAI Bubble Generator: Description and Operating Instructions. Sage Action, Inc., New York, May 1988
Basset AB (1888) A Treatise on Hydrodynamics, Volume Two, Deighton, Bell, and Co., pp 285–297
Bragg MB (1982) Rime Ice Accretion and its Effect on Airfoil Performance. NASA CR 165599, March 1982
Clift R; Grace JR; Weber ME (1978) Bubbles, Drops, and Particles. Academic Press, New York
Hale RW; Tan P; Stowell RC; Ordway DE (1971) Development of an Integrated System For Flow Visualization In Air Using Neutrally Buoyant Bubbles. SAI-RR 7107, Dec. 1971
Isenberg C (1978) The Science of Soap Films and Soap Bubbles. Tieto Ltd., England
Kerho MF (1992) A Study Of The Accuracy Of Neutrally Buoyant Bubbles Used As Flow Tracers In Air. Masters Thesis, The University of Illinois at Urbana-Champaign, pp 24–26, 74–76
Maxey MR; Riley JJ (1983) Equation of motion for a small rigid sphere in a nonuniform flow. Physics of Fluids: 26 (4),
Merzkirch W (1987) Flow Visualization. Second Edition, Academic Press, Inc., New York, pp 1, 14–51
Mueller TJ (1983) Flow visualization by direct injection. In: Fluid Mechanics Measurements (ed. Goldstein, RJ). Hemisphere Publishing Corp., New York, pp 307–352
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Kerho, M.F., Bragg, M.B. Neutrally buoyant bubbles used as flow tracers in air. Experiments in Fluids 16, 393–400 (1994). https://doi.org/10.1007/BF00202064
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00202064