Temperature characterization of a radiating gas layer using digital-single-lens-reflex-camera-based two-color ratio pyrometry

Deep, Sneh; Krishna, Yedhu; Jagadeesh, G.

doi:10.1364/ao.56.008492

Cited by 14 publications

(7 citation statements)

References 23 publications

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“…Emission spectroscopy performed in our shock tunnel also confirmed that the shock region majorly radiates as a continuous broadband source. After accounting for the spectro meter's instrument broadening, contribution from discrete line emissions due to impurities such as Na and Fe to the overall radiation intensity from the tunnel was found to be negligibly small [19]. As a result, measuring the temperature based on the broadband radiation from the soot particles due to paper and metal diaphragms, as well as from the dust particles, assuming the shock layer to be a gray-body source, would provide an indication of the conditions prevailing inside the shock tunnel.…”

Section: Introductionmentioning

confidence: 99%

“…Although the TCRP technique has been put to use in a variety of applications involving temperature measurement of radiating solid bodies or soot particles in fuel combustion [16][17][18], it was never used for shock-layer temperature characterization in short-duration facilities until recently. Deep et al [19] measured the temperature distribution within the radiating shock layer of a cylindrical body with spike using a commercial digital single lens reflex (DSLR) camera as the detector. Experiments were accomplished in a free-piston-driven shock tunnel (FPST): a ground testing impulse facility capable of simulating high-enthalpy hypersonic flow in its test section.…”

Section: Introductionmentioning

confidence: 99%

“…However, the temperature measurements performed by Deep et al [19] using a DSLR single-frame camera suffered from time integration of intensity acquired in the shock layer during the entire illuminated period. Temperatures in a shock tunnel are highest during the test time (typically a few milliseconds) and fall considerably before and after the said period.…”

Section: Introductionmentioning

confidence: 99%

“…along the LOS. This was not performed by Deep et al [19] and hence the 2D temperature obtained based on the pathintegrated signal of a flow, which is essentially 3D in nature, was assumed to be the actual temperature, and the effect of non-uniform distribution was not corrected. In the current paper, the shape of the temperature profile inside the shock layer along the LOS was interpreted by means of a numerical model of the flow field developed in Ansys Fluent 14.5, based on the Reynolds-averaged Navier-Stokes (RANS) equations.…”

Section: Introductionmentioning

confidence: 99%

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Time-resolved temperature characterization of a hypersonic shock layer using a single high-speed color camera for aerospace design applications

Deep¹,

Krishna²,

Jagadeesh³

2019

Meas. Sci. Technol.

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Two-color ratio pyrometry (TCRP) using a high-speed color camera has been used for temperature characterization of a hypersonic shock layer. The camera, used as a pyrometer, was calibrated in-house using a monochromator to determine its spectral responsivity and was used to acquire time-resolved images of the flow field over test models at a frame rate of 20 000 fps to understand the evolution of temperature inside the shock region. The optical efficiency of the monochromator and other optical equipment were determined separately and corrected for. Two test models, a flat-faced cylinder of diameter 70 mm and a hemisphere of diameter 80 mm, were used for the experiments to study the effect of geometry on the results. Experiments were performed in a free-piston-driven shock tunnel at a stagnation enthalpy of 5.2 MJ kg−1. The average steady-state temperature in the stagnation region in the cylinder was about 3650 K ± 3% (uncertainty in the shock layer due to camera noise), and for the hemisphere it was 3300 K ± 6%. The resolved temperature was 14% higher than that obtained from a similar, but time-integrated, measurement obtained using a digital single lens reflex (DSLR) camera. Steady 2D numerical simulations were performed to reconstruct the 3D flow assuming azimuthal symmetry, and an algorithm was developed to use the shape of the temperature profile along the line-of-sight (LOS) derived from simulations to predict the actual stagnation-plane temperature from the experimental LOS-integrated TCRP-derived temperature. The actual temperature in the stagnation region on the vertical plane of symmetry (stagnation plane) for the cylinder and the hemisphere were higher by 2.76% and 1.77%, respectively, than the corresponding TCRP-derived LOS-integrated temperature. The results are promising for future use in determining intense temperature gradients and heat flux in the vicinity of space vehicles and for the design of efficient thermal protection systems.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Time-resolved temperature characterization of a hypersonic shock layer using a single high-speed color camera for aerospace design applications

Deep¹,

Krishna²,

Jagadeesh³

2019

Meas. Sci. Technol.

Self Cite

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“…In the context of applying dual-color thermography to plasma wind tunnel tests, it was demonstrated by De Cesare et al[64] with an aluminum alloy square plate as a target along with thermocouple measurements for comparison. Recently TCRP has been applied, using a DSLR camera, to measure the temperature distribution in the shock layer over the test model in a hypersonic shock tunnel (HST3) at the Laboratory for Hypersonic and Shock Wave Research (LHSR), Indian Institute of Science[65]. CHAPTER 3.…”

mentioning

confidence: 99%

Ablation and radiation in hypervelocity earth-entry flows

Ravichandran¹

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Atmospheric entry of spacecraft is an interesting and challenging problem in aerospace engineering as it involves a highly non-equilibrium aerothermodynamic shock layer environment. Re-entry of spacecraft into Earth's atmosphere occurs at very high entry speeds ranging from 8-12 km · s −1 , giving rise to a bow shock wave in front of the blunt body vehicle. The associated shock layer is characterised by a very rapid increase in pressure and temperature. The kinetic energy of the hypervelocity flow is converted into thermal and chemical energy, which is partially dissipated in the form of convective and radiative heat transfer. The gases traversing the shock layer undergo thermochemical changes such as dissociation, ionisation and recombination. To safeguard the re-entry vehicle from such a harsh thermal environment, a thermal protection system (TPS) is employed on the surface of the vehicle. The TPS material, when exposed to the re-entry heating, may undergo ablation due to the combined effect of heat flux and shear from the shock layer flow. The excited gas species in the shock and boundary layer react with the atomic/molecular species ablated from the solid TPS material. However, due to the uncertainties associated with the total heat flux estimation, large safety factors are currently being used in the TPS design, particularly for the afterbody region, compromising the payload mass and vehicle safety.The main objectives of this thesis were to experimentally simulate ablation product interactions with an expanding re-entry flowfield, to characterise the radiation of the entrained ablation products using ultra-violet emission spectroscopy targeting CN radicals, and to compare the ablating flowfields with non-ablating ones. The experiments were performed in the X2 expansion tube by using a stainless steel wedge model designed with a provision to mount a graphite ablation source on its compression face. The test flow condition, representative of a point in the Hayabusa capsule re-entry trajectory, was generated in X2 with a freestream velocity of 8.6 km · s −1 and a temperature of 2500 K, corresponding to an enthalpy of 38 MJ · kg −1 . As the test times available in X2 are limited, the ablating material cannot reach such wall temperatures by aero heating alone, and hence ablation in these experiments was created by electrically preheating the graphite strip to high wall temperatures representative of re-entry conditions. The wall temperatures realised in this work ranges from 1000-3000 K, which were measured by nonintrusive filtered image thermography using a dual-wavelength signal ratio technique. The hot graphite strip, upon exposure to the re-entry flow, ablates and mixes with the flow, and passes through the expansion fan and further into the afterbody region.The flowfield and interaction processes were optically diagnosed using a high frame rate video camera, two-dimensional filtered imaging and UV emission spectroscopy. CN emission measurements were made at various locations in the flowfield such as the fore...

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