514
A. del Val et al.
temperatures which are then used to extract thermophysical properties of the heat
shield material [15]
For a comprehensive study of the properties of interest in ablators, different
experimental set-ups and techniques can be used [16]:
– High-speed cameras provide a precise estimate of the recession rate of the
material and can determine spectrometer probing locations.
– Infrared radiometers and pyrometers give information on the thermal behavior of
the test sample by detecting the electromagnetic radiation emitted. Assuming
Planck’s law for black body spectral radiance, the surface emissivity and
temperature can be derived providing insightful information about the surface
radiometry.
Away from the sample, it is important to study the gas-phase in the boundary
layer. Identification of erosion products as a function of the plasma parameters are
performed by means of optical emission spectroscopy in front of the test specimen.
Tracking ablation products in-situ during high-enthalpy testing offers an insight
on volatilization effects at the surface and in the boundary layer. The moving
surface and highly reactive boundary layer, absorbing and emitting light in multiple
spectral ranges, complicate high-precision spectroscopic measurements, such as,
for example, laser-induced spectroscopy. However, one can profit from the strong
emission of several radiators produced by the pyrolysis gases and surface ablation
for analysis of the high temperature, reacting flow, and boundary layer.
16.2.1.2 Free Stream Characterization for Validation
Validation is a vital part of any design and engineering process. Free stream
conditions in ground testing facilities are used to define the flight extrapolation
parameters and link experiments with their respective flight conditions. They are
normally rebuilt through a combination of numerical and experimental methods
resulting in their dependence upon the models used in the computational tools
employed. Ground testing facilities can also provide the experimental data needed
to validate the different simulation tools.
Experiments using optical emission spectroscopy are performed to determine
optically and non-intrusively the temperature and composition at which the spectra
detected is produced, providing the free stream conditions from experimental
diagnostics when there is no probe in the testing chamber [17]. Additional data
about the free stream can be obtained by using a high definition camera from an
optical access window to study the fluctuations of the flow and the formation of the
Mach disk in the jet during supersonic tests.
The data obtained in this manner are then processed to be used to validate the
computational models for plasma flow simulations.
A. del Val et al.
temperatures which are then used to extract thermophysical properties of the heat
shield material [15]
For a comprehensive study of the properties of interest in ablators, different
experimental set-ups and techniques can be used [16]:
– High-speed cameras provide a precise estimate of the recession rate of the
material and can determine spectrometer probing locations.
– Infrared radiometers and pyrometers give information on the thermal behavior of
the test sample by detecting the electromagnetic radiation emitted. Assuming
Planck’s law for black body spectral radiance, the surface emissivity and
temperature can be derived providing insightful information about the surface
radiometry.
Away from the sample, it is important to study the gas-phase in the boundary
layer. Identification of erosion products as a function of the plasma parameters are
performed by means of optical emission spectroscopy in front of the test specimen.
Tracking ablation products in-situ during high-enthalpy testing offers an insight
on volatilization effects at the surface and in the boundary layer. The moving
surface and highly reactive boundary layer, absorbing and emitting light in multiple
spectral ranges, complicate high-precision spectroscopic measurements, such as,
for example, laser-induced spectroscopy. However, one can profit from the strong
emission of several radiators produced by the pyrolysis gases and surface ablation
for analysis of the high temperature, reacting flow, and boundary layer.
16.2.1.2 Free Stream Characterization for Validation
Validation is a vital part of any design and engineering process. Free stream
conditions in ground testing facilities are used to define the flight extrapolation
parameters and link experiments with their respective flight conditions. They are
normally rebuilt through a combination of numerical and experimental methods
resulting in their dependence upon the models used in the computational tools
employed. Ground testing facilities can also provide the experimental data needed
to validate the different simulation tools.
Experiments using optical emission spectroscopy are performed to determine
optically and non-intrusively the temperature and composition at which the spectra
detected is produced, providing the free stream conditions from experimental
diagnostics when there is no probe in the testing chamber [17]. Additional data
about the free stream can be obtained by using a high definition camera from an
optical access window to study the fluctuations of the flow and the formation of the
Mach disk in the jet during supersonic tests.
The data obtained in this manner are then processed to be used to validate the
computational models for plasma flow simulations.