Modelling the complete operation of a free-piston shock tunnel for a low enthalpy condition

McGilvray, Matthew; Dann, Andrew; Jacobs, Peter A.

doi:10.1007/s00193-013-0437-8

Cited by 8 publications

(6 citation statements)

References 3 publications

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“…The good agreement between the reservoir enthalpy and the nozzle exit total enthalpy has a further implication. The accuracy of the method of determining the reservoir enthalpy using the measured shock speed and reservoir pressure as outlined in section 4 has been of significant interest [8]. This is assessed numerically in section 4 and the results indicated this method is accurate to within 2 % for the test conditions considered in the current work.…”

Section: The Total Enthalpymentioning

confidence: 91%

“…The exception may be if an advanced optical technique such as tuneable diode laser absorption spectroscopy [4] or coherent anti-stokes Raman spectroscopy [5] is used, but these techniques are complex, difficult to set up and generally cannot be done simultaneously with the experiments, which means an individual freestream estimate for each shot cannot be obtained. Full-facility time-accurate Navier-Stokes simulations are sometimes used to characterize these test conditions [6][7][8]; however, an obvious disadvantage is that an individual calibration for each run is impractical due to the computational time required. This is unless a perfectly steady flow is assumed and only the nozzle flow is simulated to ease the computational burden [9,10], in which case the result would not be time-resolved.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of reflected shock tunnel air conditions using a simple method

Olivier

Wen

et al. 2022

Physics of Fluids

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A new method to characterize air test conditions in hypersonic impulse facilities is introduced. It is a hybrid experimental-computational rebuilding method which uses the Fay-Riddell correlation with corrections based on thermochemical nonequilibrium computational fluid dynamic results. Its benefits include simplicity and time-resolution, and, using this method, a unique characterization can be made for each individual experimental run. Simplicity is achieved by avoiding the use of any optical techniques and overly expensive numerical computations while still maintaining accuracy. Without making any assumptions to relate the reservoir conditions to the nozzle exit conditions, the work done characterizing four test conditions in a reflected shock tunnel is presented. In this type of facility, shock compression is used to produce an appropriate reservoir which is then expanded through a nozzle to produce hypersonic flow. Particular focus is given to the nozzle exit total enthalpy where a comparison is made with the reservoir enthalpy obtained using the measured shock speed and pressure in the shock tube. Good agreement is observed in all cases providing validation of the new approach. Additionally, static pressure measurements showed clearly that conditions III and IV have a thermochemical state which likely froze shortly after the nozzle throat. Also, the nozzle flow is shown to be almost isentropic. Due to the simplicity of the current method, it can be easily implemented in existing facilities to provide an additional independent estimate alongside existing results.

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Section: The Total Enthalpymentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Characterization of reflected shock tunnel air conditions using a simple method

Olivier

Wen

et al. 2022

Physics of Fluids

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“…This scattered signal beam is coherent in nature and conveys information on the density grating due to frequency modulation of the signal intensity, according to the oscillation When acquired by a detector (e.g., photomultiplier), frequency-domain analysis of the scattered signal beam via a discrete fast Fourier transform (DFT) yields the oscillation frequency f M of the induced density grating. Thus, provided the grating constant Λ and nature of the grating (electrostrictive or thermal) are known a priori, the speed of sound within the measurement volume can be calculated from (3). For a known gas composition, local temperature of the single-point sample volume spanned by the interference pattern can be calculated from the associated speed of sound.…”

Section: Measurement Principlementioning

confidence: 99%

“…For means of consistency with data analysis at test conditions, real gas (equation of state) values according to Lemmon et al [38] are similarly utilized for calibration purposes. Henceforth, the interference fringe spacing (optical grating constant) Λ is uniquely determined according to (3).…”

Section: Calibration Proceduresmentioning

confidence: 99%

“…Typically, total flow enthalpy is determined by quasi one-dimensional (1-D) numerical codes such as L1d, ESTCj [3], or Kasimir [4] based on incident shock Mach number and assuming normal shock relations [5] as well as quasi-steady conditions thereafter, as long as test conditions are properly tailored. In practice, physical three-dimensional (3-D) phenomena are more complex due to the presence of the shock tube wall boundary layer and endwall-reflected shock bifurcation such that post-reflected conditions in a reflected shock tunnel can vary over time [6].…”

Section: Introductionmentioning

confidence: 99%

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In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

2021

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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.

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Quasi-one-dimensional non-equilibrium method for shock tube and stagnation line flows

Clarke,

Brody,

Steer

et al. 2024

Physics of Fluids

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Shock tube experiments are used to investigate non-equilibrium thermochemistry and radiative processes in reacting gas hypersonic flows. Boundary layer and shock structure are known to influence the spatial variation of the test slug state properties. This work derives and validates a novel method for viscous, quasi-one-dimensional, non-equilibrium flow in a shock tube assuming constant shock speed. The proposed method fully resolves the shock structure. Mirels' estimate for boundary layer growth around the test slug determines the dilation rate at the centerline. This, along with relevant boundary conditions, appropriately models core flow in a shock tube. The flow equations are discretized by finite differences on a staggered grid. The resulting highly non-linear set of algebraic equations is solved by Newton iterations. The Jacobian matrix is block tridiagonal with a Schur complement, allowing efficient inversion. This culminates in a unique and computationally efficient quasi-one-dimensional method offering improved modeling of the physical characteristics of shock tube experiments. Results of a 3 km/s, 66.6 Pa argon test case solved by a viscous, axisymmetric Navier–Stokes solution had agreement with the proposed method in temperature and pressure profiles to within 2% and post-shock velocity to within 15%. Reacting gas shock tube experiments in synthetic air and synthetic Titan atmospheres were analyzed. Radiance values in the non-equilibrium and equilibrium regions were compared under various assumptions for the shock structure and radial velocity distribution. These results highlight the necessity of a dedicated shock tube solver when analyzing shock tube thermochemistry, particularly when determining reaction rates and relaxation parameters.

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Modelling the complete operation of a free-piston shock tunnel for a low enthalpy condition

Cited by 8 publications

References 3 publications

Characterization of reflected shock tunnel air conditions using a simple method

Characterization of reflected shock tunnel air conditions using a simple method

In situ nozzle reservoir thermometry by laser-induced grating spectroscopy in the HELM free-piston reflected shock tunnel

Quasi-one-dimensional non-equilibrium method for shock tube and stagnation line flows

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