Non-equilibrium Kinetics behind Shock Waves Experimental Aspects

Ibraguimova, L. B.; Shatalov, O. P.

doi:10.1007/978-3-642-25119-1_4

Cited by 5 publications

(4 citation statements)

References 144 publications

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“…Therefore, the result indicates that the vibrational relaxation in expanding flows is faster than the vibrational relaxation behind shock waves. This result for high temperature CO2 is consistent with previous experimental results for N2 and CO [66] [75], as well as CO2 at lower temperatures [50].…”

Section: Resultssupporting

confidence: 93%

“…This showed that the CO2 vibrational relaxation is significantly faster in expanding flow conditions than in postshock conditions. This result is consistent with results from numerous expanding flow experiments which were done for N2 and CO [66] [75], as well as CO2 at lower temperatures [50]. A possible consequence of having small non-equilibrium between the rotational mode and the vibrational mode of CO2 is that complex non-equilibrium effects, such as non-equilibrium between the different vibrational modes of CO2 and non-Boltzmann distribution within vibrational energy levels, are likely negligibly small in the expanding flow.…”

Section: Discussionsupporting

confidence: 92%

“…Lastly, it is important to mention that Sharma et al [65] [66] stated that previous studies of diatomic species N2 and CO indicated the vibrational relaxation time in expanding flows can be up to two orders of magnitude faster than the relaxation time behind shock waves. These past results for N2 and CO are consistent with the past result for CO2 at lower temperatures [50], as mentioned in the previous section.…”

Section: Experimental Studies Of High Enthalpy Expanding Flowssupporting

confidence: 92%

“…Very little experimental work relating to non-equilibrium CO2 expanding flows can be found in past literature. A study of low temperature, T=600 -1400 K, CO2 expansion through a nozzle showed that the vibrational de-excitation in the expansion is 1.1 ± 0.4 times faster than the vibrational excitation behind shock waves [50]. Another notable work on CO2 expanding flows would be that of Maclean and Holden [51].…”

Section: Carbon Dioxide Thermochemistry and Radiationmentioning

confidence: 99%

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Mars entry afterbody radiative heating: an experimental study of nonequilibrium CO2 expanding flow

Gu¹

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This thesis presents an experimental study of high temperature CO2 flowsfocusing on CO2 flows subjected to rapidly expanding conditions relevant to Mars entry and representative of the corner expansion around the shoulder, between the windward and leeward flows, on an entry capsule. This is an important but poorly understood aspect of spacecraft design. Past numerical research showed that, during Mars entry, the CO2 4.3 µm and 2.7 µm band radiation from the aforementioned expanding flow produce non-negligible contributions to the heating of the capsule afterbody.Consequently, this radiative heating should be considered in the sizing of the afterbody thermal protection systems (TPS). However, due to a lack of experimental research, the nonequilibrium characteristics of CO2 expanding flows are not well understood. Therefore, to help with the design of future Mars entry vehicles, it is necessary to investigate such flows.The X2 expansion tube was used to facilitate the current study. Three expansion tube test conditions with differing velocitiesnominally 2.8 km/s, 3.4 km/s, and 4.0 km/swere developed. Using a two-dimensional wedge model with a 54° convex corner along with the new conditions, flows with similarities to the expanding flow around the shoulder of an aeroshell at certain Mars entry conditions were created. Mid-wavelength infrared emission spectroscopy of the 4.3 μm and 2.7 μm bands were performed on the flow. The spectroscopic measurements were used to estimate the rotational and vibrational temperatures and the CO2 number densities using a spectral fitting method. Supplementing the spectroscopic measurements, filtered images of the 4.3 μm and 2.7 μm bands were taken to provide a two-dimensional spatial map of the band radiance in the flow around the wedge. Estimates of the experimental inflow conditions were produced by solving for the intermediate test gas states using measurements of various properties of the operating condition. CO2 spectroscopic measurements of the inflow along with measurements of the wedge model shock location and deduced post-shock conditions were also used to help characterize the test conditions. Using estimated inflow conditions, three-dimensional CFD simulations of the experiments were conducted using a two-temperature model. The computed results were compared to the available measurements to examine the appropriateness of the current numerical model at simulating the CO2 flow.Important qualitative results were obtained in this thesis in regards to the high temperature CO2expanding flow. The temperatures estimated in the wedge flow using both the 2.7 and 4.3 µm spectroscopic measurements were found to be the same. This provides some confidence to the validity of NEQAIR, using CDSD-4000, at predicting CO2 radiation under gas-dynamic conditions which are more relevant to Mars entry. Using the estimated rotational and vibrational temperatures, the CO2 II thermal non-equilibrium in the expanding flow was shown to be smallless than 10%. As the experiments simulate the expanding fl...

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Section: Resultssupporting

confidence: 93%

Section: Discussionsupporting

confidence: 92%