Optical imaging techniques for hypersonic
                                                impulse facilities

McIntyre, Timothy J.; Kleine, H.; Houwing, A. F. P.

doi:10.1017/s0001924000001718

Cited by 15 publications

(4 citation statements)

References 84 publications

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“…In the light of excessive pressure levels prevalent in high-enthalpy ground testing, the positive correlation of resonant and non-resonant LIGS signal intensity with fluid pressure is considered particularly advantageous. Whereas quantitative measurements by a range of competitive techniques are increasingly impeded at elevated pressures-resultant from a decaying signal strength due to higher collisional quenching rates [19,25]-the signal intensity I of LIGS benefits from greater pressures p and rises according to (1) [26]:…”

Section: Ligs Applicationmentioning

confidence: 99%

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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Section: Ligs Applicationmentioning

confidence: 99%

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

2021

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“…The short test time and complicated flow phenomena, such as shocks and extreme variations, impose interesting challenges on the flow diagnostics. The various diagnostic techniques employed in these facilities are measurements of surface pressure, temperature/heat transfer [6,7], skin friction [8], aerodynamic forces and moments [9], qualitative flow field visualizations using Schlieren/shadowgraph techniques, and density field measurements using interferometry [10][11][12]. Surface pressure measurements are essential for computing aerodynamic drag forces and moments, as well as the unsteadiness of the flow [13].…”

Section: Introductionmentioning

confidence: 99%

Simultaneous measurement of pressure and temperature in a supersonic ejector using FBG sensors

Hegde¹,

Himakar²,

V³

et al. 2022

Meas. Sci. Technol.

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In this work, we have demonstrated the use of Fiber Bragg Grating (FBG) sensors for simultaneous measurement of wall static pressure and temperature in a supersonic ejector. Supersonic ejectors are ground based high speed aerodynamic test facilities characterized by harsh conditions such as high pressure and temperature gradients. FBG based sensor setup was developed consisting of pressure measuring bare FBG and specially designed pressure-insensitive FBG temperature probe that could be mounted on the wall of the supersonic ejector. The FBG temperature probe was used for temperature measurement as well as temperature compensation of pressure measuring FBG sensor. Wall static pressure measurements in the supersonic ejector were carried out at different tank pressures and Mach number flows. The FBG pressure measurements were validated with that of standard piezoresistive based sensor measurements. Both the responses were found to match closely with FBG sensor having a faster response time and higher pressure resolution. Fluid structure interaction simulation was carried out in Comsol Multiphysics to understand the interaction of high speed turbulent flow on the fiber based FBG sensor. The FBG strain profile due to flow-induced stress and its dependence on flow pressure was studied. A detailed analysis of effect of preceding fiber length on FBG pressure measurement was carried out. FBG sensors, owing to their miniature size, ability to withstand harsh environments and multi parameter sensing capability can be used in ground-based aerodynamic test facilities with minimum intrusion to the flow.

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“…Many optical techniques such as schlieren, shadowgraph, holographic interferometry, particle image velocimetry (PIV), background oriented schlieren (BOS) [17][18][19][20], shadow-casting [21,22], laser induced fluorescence (LIF) [17,18] are extensively used in flow visualization in supersonic and hypersonic regimes in shock tunnels and wind tunnels. Among these, schlieren and shadowgraph schemes provide 2D projected qualitative images of the 3D domain, represented in intensity scale.…”

Section: Introductionmentioning

confidence: 99%

Time-resolved quantitative visualization of complex flow field emitted from an open ended shock tube using a wavefront measuring camera

Medhi

Hegde

Reddy

2019

Optics and Lasers in Engineering

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Quantitative visualization of shock induced complex flow field emanating from the open end of a miniaturized hand-driven shock tube (Reddy tube) is presented. During operation, the planar shock wave of Mach number M i =1.33 (±0.6%) is discharged through the low-pressure driven-section, kept open to ambient atmosphere. From the moment of shock discharge, its aftereffects of evolving flow field are recorded for 300 s  near the exit of the tube by using our newly developed high resolution (16Mpixel) home built wavefront measuring camera setup. The ability of the camera to identify the amplitude and phase of the incident light wave is utilized to measure the flow induced change in phase of the interrogating light beam quantitatively. Information of the evolving flow field with a spatial resolution of 16μm/pixel and time resolution of 50 s  is recorded in repeated runs. The measured phase information is used in an iterative refraction tomographic scheme to recover the 3D-density distribution of the flow field, which reveals the internal features of the domain. Computational fluid dynamic (CFD) simulation is carried out for the same experimental conditions and it is found that recovered experimental density distribution shows good agreement with the results obtained through CFD simulation.

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Optical imaging techniques for hypersonic impulse facilities

Cited by 15 publications

References 84 publications

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

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

Simultaneous measurement of pressure and temperature in a supersonic ejector using FBG sensors

Time-resolved quantitative visualization of complex flow field emitted from an open ended shock tube using a wavefront measuring camera

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