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Conditional sampling of velocity and scalars in turbulent flames using simultaneous LDV-Raman scattering

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Abstract

The laser Doppler velocimeter (LDV) measures the velocity distribution of particles which is often an acceptable representation of the distribution of gas velocities. However, in turbulent two stream mixing flows, the particle velocity distribution will differ from the gas velocity distribution when the particle densities in the two streams are unequal. This bias is explored in a reacting and nonreacting turbulent jet which is surrounded by coflowing air. By adding seed particles to only the coflow air and then to only the jet fluid, the limits of this bias are established. Additional measurements with an LDV triggered laser Raman scattering system demonstrate that the bias in the LDV sampling is propagated to the Raman measurements. An analytical equation is presented which will generate unbiased velocity and scalar distributions from measurements obtained from seeding only one stream at a time.

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Abbreviations

f :

mixture fractionf = 1 in nozzle,f = 0 in coflow air

P(f):

probability distribution of mixture fraction

P(u, v):

joint probability distribution of axial and radial velocity

P(u, v, f):

joint probability distribution of axial and radial velocity and of mixture fraction

P(u, v, f X (r, τ)):

is the probability ofu, v, andf, conditioned onX (r, τ)

Re D :

Reynolds based on mean velocity and pipe diameterD

u :

axial velocity

v :

radial velocity

\(u' = \bar u - u\) :

fluctuation from mean axial velocity

\(v' = \bar v - v\) :

fluctuation from mean radial velocity

\(\overline {u'v'} \) :

correlation of axial and radial velocity fluctuations

x :

axial position downstream from nozzle exit

y :

radial position from centerline

r :

spatial position of measurement

X air/jet(r, τ):

initial position of a fluid element which arrives at the spatial pointr after a time τ from the jet or from the coflow air

Δλ:

laser linewidth, full width at half maximum

γ:

probability that a given fluid element originated from the jet

λ:

wavelength

λ0 :

wavelength at which half-wave plate rotates light by 90 degrees

μm:

microns = 10−6 meters

\(\bar \varphi \) :

time averaged value of argument

air:

LDV particles added to coflow air only

calc:

calculated value

jet:

LDV particles added to jet fluid only

rms:

root mean square value

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Authors and Affiliations

  1. Sandia National Laboratories, 94550, Livermore, CA, USA

    R. W. Dibble, V. Hartmann & R. W. Schefer

  2. Dept. of Mechanical Engineering, University of California, 95616, Davis, CA, USA

    W. Kollmann

Authors
  1. R. W. Dibble
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  2. V. Hartmann
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  3. R. W. Schefer
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  4. W. Kollmann
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Additional information

A version of this paper was presented at the ASME Winter Annual Meeting of 1984 and printed in AMD-Vol. 66

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Dibble, R.W., Hartmann, V., Schefer, R.W. et al. Conditional sampling of velocity and scalars in turbulent flames using simultaneous LDV-Raman scattering. Experiments in Fluids 5, 103–113 (1987). https://doi.org/10.1007/BF00776180

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  • DOI: https://doi.org/10.1007/BF00776180

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