12.6 Laser-Induced Fluorescence (LIF)
269
Fig. 12.8 Principle of Planar Induced Fluorescence, or PLIF
small facilities; except if acetone is used. The quenching phenomenon further limits
the application of LIF to pressures below atmospheric pressure.
Fluorescence properties are also used to obtain an image of a flow region using
the Planar Laser Induced Fluorescence or PLIF (see Fig. 12.8). In this technique, the
area of interest is illuminated by a laser sheet and the fluorescence image recorded
by a camera containing a two-dimensional matrix of photo-detectors. In general, the
camera records and digitises the fluorescence intensity associated with the absorption for a single spectral function; hence the ability to determine the velocity, the
temperature or the concentration fields according to the chosen function.
The flow velocity is deduced from the overall Doppler shift of the radiated signal.
To accurately determine velocity, this method requires either measurement techniques sensitive to small frequency variations or sufficiently large flow velocities.
To allow measurement of low velocities, a flow marking technique can be used in
which a small volume of fluid is marked by a laser-induced process. Due to its
long relaxation period, LIF allows tracking this volume convected downstream after
a specified time interval. With this technique, velocities can be measured without
strong requirements on the spectroscopic qualities of the signal. In this application,
LIF is superior to LDV because it measures the velocity of atoms and molecules
whereas LDV gives the velocity of particles much larger than the constituents of
the gas. In practice, the good functioning of LIF remains delicate and complex. In
addition, LIF only operates in a well-defined regime of pressure.
12.7 Electron Beam-Induced Fluorescence (EBF)
Electron Beam Fluorescence (EBF) is a technique well-suited for non-intrusive local
measurements of density, vibrational and rotational temperatures in a low-density
269
Fig. 12.8 Principle of Planar Induced Fluorescence, or PLIF
small facilities; except if acetone is used. The quenching phenomenon further limits
the application of LIF to pressures below atmospheric pressure.
Fluorescence properties are also used to obtain an image of a flow region using
the Planar Laser Induced Fluorescence or PLIF (see Fig. 12.8). In this technique, the
area of interest is illuminated by a laser sheet and the fluorescence image recorded
by a camera containing a two-dimensional matrix of photo-detectors. In general, the
camera records and digitises the fluorescence intensity associated with the absorption for a single spectral function; hence the ability to determine the velocity, the
temperature or the concentration fields according to the chosen function.
The flow velocity is deduced from the overall Doppler shift of the radiated signal.
To accurately determine velocity, this method requires either measurement techniques sensitive to small frequency variations or sufficiently large flow velocities.
To allow measurement of low velocities, a flow marking technique can be used in
which a small volume of fluid is marked by a laser-induced process. Due to its
long relaxation period, LIF allows tracking this volume convected downstream after
a specified time interval. With this technique, velocities can be measured without
strong requirements on the spectroscopic qualities of the signal. In this application,
LIF is superior to LDV because it measures the velocity of atoms and molecules
whereas LDV gives the velocity of particles much larger than the constituents of
the gas. In practice, the good functioning of LIF remains delicate and complex. In
addition, LIF only operates in a well-defined regime of pressure.
12.7 Electron Beam-Induced Fluorescence (EBF)
Electron Beam Fluorescence (EBF) is a technique well-suited for non-intrusive local
measurements of density, vibrational and rotational temperatures in a low-density