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Temperature and velocity determination of shock-heated flows with non-resonant heterodyne laser-induced thermal acoustics

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Non-resonant laser-induced thermal acoustics (LITA), a four-wave mixing technique, was applied to post-shock flows within a shock tube. Simultaneous single-shot determination of temperature, speed of sound and flow velocity behind incident and reflected shock waves at different pressure and temperature levels are presented. Measurements were performed non-intrusively and without any seeding. The paper describes the technique and outlines its advantages compared to more established laser-based methods with respect to the challenges of shock tube experiments. The experiments include argon and nitrogen as test gas at temperatures of up to 1000 K and pressures of up to 43 bar. The experimental data are compared to calculated values based on inviscid one-dimensional shock wave theory. The single-shot uncertainty of the technique is investigated for worst-case test conditions resulting in relative standard deviations of 1, 1.7 and 3.4 % for Mach number, speed of sound and temperature, respectively. For all further experimental conditions, calculated values stay well within the 95 % confidence intervals of the LITA measurement.
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DOI 10.1007/s00340-015-6217-7
Appl. Phys. B (2015) 121:235–248
Temperature and velocity determination of shock‑heated flows
with non‑resonant heterodyne laser‑induced thermal acoustics
F. J. Förster1 · S. Baab1 · G. Lamanna1 · B. Weigand1
Received: 13 July 2015 / Accepted: 1 September 2015 / Published online: 21 September 2015
© Springer-Verlag Berlin Heidelberg 2015
Challenges arising from measurements in impulse facili-
ties are briefly addressed followed by a discussion of LITA
with respect to more established techniques. An overview
of existing studies using LITA in shock-induced flows is
given to clarify the resulting motivation of the presented
work.
Shock tubes are widely used in a variety of scientific
applications, which feature high pressure and temperature
environments (e.g. shock-induced flows [1], combustion
chemistry [2], fluid disintegration [3] and reentry phys-
ics [4]). However, quantitative measurements under such
conditions are inherently challenging. In addition, the
very short test duration requires fast-response techniques.
Acquiring multiple gas properties from a single experiment
is desirable as turn-around times and operational costs may
be considerable.
Conventional probing techniques as employed in wind
tunnels are intrusive, which make measurements inside
the flow field difficult due to interference with the flow.
Sensors embedded into the model or shock tube wall are
commonly used to measure pressure. For temperature, this
is more challenging as—in contrast to pressure—tempera-
tures measured at the surface and inside the flow may differ
significantly due to the boundary layer [5].
Laser-based techniques can potentially overcome all
these problems. In addition to well-established tech-
niques such as tunable diode laser absorption spectroscopy
(TDLAS) [6, 7], laser-induced fluorescence (LIF) [810]
or coherent anti-Stokes Raman spectroscopy (CARS)
[11, 12], the authors evaluate LITA as a diagnostic tool
for pulsed facilities. For temperature measurements after
reflected shock waves similar to those used in this study,
Farooq et al. [13] reported a relative standard deviation of
0.5 % for TDLAS. Furthermore, mean discrepancies to the-
oretical values of 3.6 % were found for LIF [9]. Precision
Abstract Non-resonant laser-induced thermal acous-
tics (LITA), a four-wave mixing technique, was applied to
post-shock flows within a shock tube. Simultaneous single-
shot determination of temperature, speed of sound and
flow velocity behind incident and reflected shock waves
at different pressure and temperature levels are presented.
Measurements were performed non-intrusively and with-
out any seeding. The paper describes the technique and
outlines its advantages compared to more established laser-
based methods with respect to the challenges of shock tube
experiments. The experiments include argon and nitrogen
as test gas at temperatures of up to 1000 K and pressures
of up to 43 bar. The experimental data are compared to cal-
culated values based on inviscid one-dimensional shock
wave theory. The single-shot uncertainty of the technique
is investigated for worst-case test conditions resulting in
relative standard deviations of 1, 1.7 and 3.4 % for Mach
number, speed of sound and temperature, respectively. For
all further experimental conditions, calculated values stay
well within the 95 % confidence intervals of the LITA
measurement.
1 Introduction
The paper presents laser-induced thermal acoustics (LITA)
as diagnostic tool for shock tube facilities. LITA combines
a number of desirable features including non-intrusive,
seedless point measurements of several flow properties.
* F. J. Förster
felix.foerster@itlr.uni-stuttgart.de
1 Institute of Aerospace Thermodynamics (ITLR), University
of Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Further challenges for the measurement technique are the extremely high temperature and pressure as well as the very short measurement time in the nozzle reservoir of shock tunnels, which can be overcome by optical measurement techniques. Homodyne laserinduced thermal grating spectroscopy (LITGS, also called resonant LIGS or resonant LITA) needs no seeding particles and offers the possibility of temperature measurements with a high temporal resolution [3][4][5][6][7] under single-shot conditions. In addition, only a small optical access is required for this method, which is particularly advantageous for measurements under high temperatures and pressures. ...
... In the literature, different values can be found for x and y, which also differ between the procedures electrostrictive (LIEGS, also called non-resonant LIGS or non-resonant LITA) and LITGS. In the work of Förster et al. [7], the value 2 is given for x and -3.4 for y for LIEGS. Schlamp et al. [8] report, deviating from this, y = −3 (fluid at rest) or y = −4.25 (flowing fluid). ...
... A more recent work on measurements with laser-induced gratings can be found in Förster [7]. The experimental setup used is basically based on those of Schlamp et al. [16] and Hemmerling et al. [17]. ...
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... The shock tube was spatially fixed in a foundation such that no recoil occurred to induce deflection and laser beam misalignment throughout the experiment. In a similar small-sized conventional, spatially fixed shock tube, Förster et al. [28] presented simultaneous single-shot temperature and velocity measurements by non-resonant heterodyne LIGS. Experiments in nitrogen and argon at shock Mach numbers 1.67-1.96 ...
... Alternatively, a so-called heterodyne approach uses a second interrogation beam as local oscillator (i.e., reference beam) not passing the measurement volume but being mixed with the signal beam from the measurement volume prior to detection. Interference of both signal and reference beams enables additional quantification of the local bulk fluid velocity (single component) from the oscillation beat frequency and Doppler shift-thus enabling direct, simultaneous measurement of local flow Mach number via sound speed and fluid velocity; compare Förster et al. [28]. The present study solely applies the homodyne approach as quantification of fluid residual velocity components in the high-vorticity, post-reflected shock state 5 is not considered of interest. ...
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Experimental determination of test gas caloric quantities in high-enthalpy ground testing is impeded by excessive pressure and temperature levels as well as minimum test timescales of short-duration facilities. Yet, accurate knowledge of test gas conditions and stagnation enthalpy prior to nozzle expansion is crucial for a valid comparison of experimental data with numerical results. To contribute to a more accurate quantification of nozzle inlet conditions, an experimental study on non-intrusive in situ measurements of the post-reflected shock wave stagnation temperature in a large-scale free-piston reflected shock tunnel is carried out. A series of 20 single-shot temperature measurements by resonant homodyne laser-induced grating spectroscopy (LIGS) is presented for three low-/medium-enthalpy conditions (1.2–2.1 MJ/kg) at stagnation temperatures 1100–1900 K behind the reflected shock wave. Prior limiting factors resulting from impulse facility recoil and restricted optical access to the high-pressure nozzle reservoir are solved, and advancement of the optical set-up is detailed. Measurements in air agree with theoretical calculations to within 1–15%, by trend reflecting greater temperatures than full thermo-chemical equilibrium and lesser temperatures than predicted by ideal gas shock jump relations. For stagnation pressures in the range 9–22 MPa, limited influence due to finite-rate vibrational excitation is conceivable. LIGS is demonstrated to facilitate in situ measurements of stagnation temperature within full-range ground test facilities by superior robustness under high-pressure conditions and to be a useful complement of established optical diagnostics for hypersonic flows.
... A radial piston pump or a pressurized fluid reservoir provides the required injection pressures depending on the desired NPRs in the experiments. A more detailed description of the test facilities is given in [43,36,44]. ...
... For a detailed description of the optical arrangement the reader is referred to Förster et al. [44] and Baab et al. [36]. Here, only the essential information are given. ...
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... This link is provided by a simple scaling constant providing a significantly simpler calibration procedure. In recent studies, we proved the effectiveness of LITA for quantitative speed of sound measurements in high-pressure atmospheres [37] and the turbulent far-field zone of extremely underexpanded jets [38]. ...
... We determined Λ from frequency measurements in pure nitrogen at ambient conditions for which the speed of sound is well-known. The uncertainties from this calibration procedure can be considered to be within 1.3 % as it was found in Förster et al. [37]. ...
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This study is the first to provide a comprehensive speed of sound database for multi-component jet mixing at high pressure. It serves as a unique reference for numerical simulations of mixture preparation processes in future liquid rocket engines and internal combustion engines. We performed quantitative speed of sound measurements in jet mixing zones for five configurations with well-defined experimental conditions. The database covers three different injectant fluids (two alkanes and a fluoroketone) that were brought beyond their critical temperature and pressure prior to injection and discharged into cold nitrogen at supercritical pressure (with respect to the pure injectant properties). Here, we chose the conditions such that subsonic jets were obtained and re-condensation due to cooling of the injected fluid was prevented. Hence, we provide speed of sound data for single-phase jet mixing for three different binary systems. Quantitative data are presented along the jet centerline with sufficiently high spatial resolution to properly resolve the axial decay. In addition, two radial profiles at a position close to the nozzle allow for an assessment of the transversal mixing characteristics. The experimental speed of sound data show consistent trends, which corroborate that mixture effects are correctly resolved in the measurement.
... Three different atmospheres, namely nitrogen with a purity of 99.999 % , argon with a purity of 99.998 % , and carbon dioxide with a purity of 99.995 % , are studied. The optical setup is adapted from the one described in Baab et al. (2016) and Förster et al. (2015). ...
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... The technique has also been successfully applied to calibration of Two-Colour Planar Laser Induced Fluorescence imaging of temperature distributions in a firing engine [10] . Recent developments have also included applications in shock tubes and high-speed fuel injection jets and mixing [11,12] . ...
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... ment and data acquisition system is sketched in Fig. 3 . A detailed characterization of the shock tube facility can be found e.g. in Förster et al. (2015) . ...
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