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Image processing of hydrogen bubble flow visualization for determination of turbulence statistics and bursting characteristics

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Abstract

A technique is described which employs automated image processing of hydrogen-bubble flow visualization pictures to establish local, instantaneous velocity profile information. Hydrogen bubble flow visualization sequences are recorded using a high-speed video system and then digitized, stored, and evaluated by a VAX 11/780 computer. Employing special smoothing and gradient detection algorithms, individual bubble-lines are computer identified, which allows local velocity profiles to be constructed using time-of-flight techniques. It is demonstrated how this techniques may be used to 1) determine local velocity behavior as a function of position and time, 2) evaluate time-averaged turbulence properties, and 3) correlate probe-type turbulent burst detection techniques with the corresponding visualization data.

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Abbreviations

Re θ :

Reynolds number based on momentum thickness, ≡u ∞θ/ν

t + :

nondimensional time ≡tu 2 τ/θ

T :

VITA variance averaging time period

u τ :

shear velocity =\(\sqrt {\tau _w /\varrho } \)

u :

local instantaneous streamwise velocity,x-direction

u :

local fluctuating streamwise velocity,x-direction

u + :

nondimensional streamwise velocity,≡\(\bar u\)/u τ

ν:

local normal velocity,y-direction

w :

local spanwise velocity,z-direction

x + :

nondimensional coordinate in streamwise direction ≡xu τ /v

y + :

nondimensional coordinate normal to wall, ≡yu τ /v

θ:

momentum thickness,\(\int\limits_0^\delta {\frac{{\bar u}}{{u_\infty }}\left( {1 - \frac{{\bar u}}{{u_\infty }}} \right) } dy\)

ν:

kinematic viscosity

τ w :

wall shear stress

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Authors and Affiliations

  1. Department of Mechanical Engineering and Mechanics, Lehigh University, 18015, Bethlehem, Pennsylvania, USA

    L. J. Lu & C. R. Smith

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  1. L. J. Lu
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  2. C. R. Smith
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Lu, L.J., Smith, C.R. Image processing of hydrogen bubble flow visualization for determination of turbulence statistics and bursting characteristics. Experiments in Fluids 3, 349–356 (1985). https://doi.org/10.1007/BF01830195

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