Experiments in Fluids

, Volume 45, Issue 5, pp 899–915

Optical plume velocimetry: a new flow measurement technique for use in seafloor hydrothermal systems

  • Timothy J. Crone
  • Russell E. McDuff
  • William S. D. Wilcock
Research Article

DOI: 10.1007/s00348-008-0508-2

Cite this article as:
Crone, T.J., McDuff, R.E. & Wilcock, W.S.D. Exp Fluids (2008) 45: 899. doi:10.1007/s00348-008-0508-2

Abstract

Evidence suggests that fluid flow rates in mid-ocean ridge hydrothermal systems may be strongly influenced by mechanical forces such as ocean tidal loading. However, long time-series measurements of flow have not been collected in these environments. We develop a non-invasive method, called optical plume velocimetry (OPV), suitable for obtaining fluid flow rates through black smoker vents based on image analysis of effluent video. We use video from laboratory flows to evaluate three different methods for estimating the image-velocity field that are based on region-based matching, spectral-analysis of Hovmöller diagrams, and temporal cross-correlation of adjacent pixel values. We find that OPV is most sensitive and least biased when the cross-correlation method is used and conclude that OPV should not be applied to flows that are transitioning between jet-like and plume-like behavior.

List of symbols

A

area of jet nozzle, m2

B

initial specific buoyancy flux, m4/s3

c1

constant in along-axis plume velocity equation

cf

fraction of Nyquist frequency for Hovmöller cut-off

C

temporal cross-correlation function

D

jet nozzle diameter, m

d

pixel separation in temporal cross-correlation method, pixels

f

frequency, 1/s

g

gravitational acceleration, m/s2

k1

constant in along-axis jet velocity equation

lM

Morton length scale, m

lmax

lag number at the cross-correlation maximum, frames

M

initial specific momentum flux, m4/s2

n

number of instantaneous image-velocity measurements used to calculate the mean

N

number of frames in image sequence

Q

nozzle flow rate, m3/s

Qi

individual nozzle flow rate measurement, l/s

Qm

mean measured nozzle flow rate, 1/s

r

radial coordinate, m

R

Residual for region-based matching image-velocity estimation

Re

Reynolds number

S

standard deviation

Δt10

time for source fluid tank level to drop by 10 l, s

\(\bar{u}\)

flow velocity, m/s

t

time, s

up

instantaneous image-velocity, pixels/frame

\(\overline{u_p}\)

mean image-velocity, pixels/frame

Um

mean along-axis jet velocity, m/s

Up

flow rate metric, pixels/frame

W

mean flow velocity across jet nozzle, m/s

Wp

mean flow velocity across jet nozzle converted to pixels per second, pixels/frame

x

horizontal coordinate, m

xp

projected horizontal coordinate, pixels

z

vertical coordinate, m

zp

projected vertical coordinate, pixels

Greek symbols

λp

flow feature wavelength, pixels

ν

Hovmöller FFT wave number, 1/pixels

μ

viscosity of jet fluid, Pa s

ρ

density of ambient fluid, kg/m3

ρJ

density of jet fluid, kg/m3

Δρ

density difference between jet and ambient fluid, kg/m3

Supplementary material

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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Timothy J. Crone
    • 1
  • Russell E. McDuff
    • 2
  • William S. D. Wilcock
    • 2
  1. 1.Lamont-Doherty Earth ObservatoryColumbia UniversityPalisadesUSA
  2. 2.School of OceanographyUniversity of WashingtonSeattleUSA