Current Search: Reflected Shock (x)
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- Title
- NUMERICAL MODELING OF THE SHOCK TUBE FLOW FIELDS BEFORE ANDDURING IGNITION DELAY TIME EXPERIMENTS AT PRACTICAL CONDITIONS.
- Creator
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lamnaouer, mouna, Kassab, Alain, University of Central Florida
- Abstract / Description
-
An axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A&M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to...
Show moreAn axi-symmetric shock-tube model has been developed to simulate the shock-wave propagation and reflection in both non-reactive and reactive flows. Simulations were performed for the full shock-tube geometry of the high-pressure shock tube facility at Texas A&M University. Computations were carried out in the CFD solver FLUENT based on the finite volume approach and the AUSM+ flux differencing scheme. Adaptive mesh refinement (AMR) algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous and reactive effects. A conjugate heat transfer model has been incorporated which enhanced the credibility of the simulations. The multi-dimensional, time-dependent numerical simulations resolved all of the relevant scales, ranging from the size of the system to the reaction zone scale. The robustness of the numerical model and the accuracy of the simulations were assessed through validation with the analytical ideal shock-tube theory and experimental data. The numerical method is first applied to the problem of axi-symmetric inviscid flow then viscous effects are incorporated through viscous modeling. The non-idealities in the shock tube have been investigated and quantified, notably the non-ideal transient behavior in the shock tube nozzle section, heat transfer effects from the hot gas to the shock tube side walls, the reflected shock/boundary layer interactions or what is known as bifurcation, and the contact surface/bifurcation interaction resulting into driver gas contamination. The non-reactive model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave. Both the inviscid and the viscous non-reactive models provided a baseline for the combustion model iii which involves elementary chemical reactions and requires the coupling of the chemistry with the flow fields adding to the complexity of the problem and thereby requiring tremendous computational resources. Combustion modeling focuses on the ignition process behind the reflected shock wave in undiluted and diluted Hydrogen test gas mixtures. Accurate representation of the Shock –tube reactive flow fields is more likely to be achieved by the means of the LES model in conjunction with the EDC model. The shock-tube CFD model developed herein provides valuable information to the interpretation of the shock-tube experimental data and to the understanding of the impact the facility-dependent non-idealities can have on the ignition delay time measurements.
Show less - Date Issued
- 2010
- Identifier
- CFE0003011, ucf:48366
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003011
- Title
- WALL HEAT TRANSFER EFFECTS IN THE ENDWALL REGION BEHIND A REFLECTED SHOCK WAVE AT LONG TEST TIMES.
- Creator
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Frazier, Corey, Petersen, Eric, University of Central Florida
- Abstract / Description
-
Shock-tube experiments are typically performed at high temperatures (>1200K) due to test-time constraints. These test times are usually ~1 ms in duration and the source of this short, test-time constraint is loss of temperature due to heat transfer. At short test times, there is very little appreciable heat transfer between the hot gas and the cold walls of the shock tube and a high test temperature can be maintained. However, some experiments are using lower temperatures (approx. 800K) to...
Show moreShock-tube experiments are typically performed at high temperatures (>1200K) due to test-time constraints. These test times are usually ~1 ms in duration and the source of this short, test-time constraint is loss of temperature due to heat transfer. At short test times, there is very little appreciable heat transfer between the hot gas and the cold walls of the shock tube and a high test temperature can be maintained. However, some experiments are using lower temperatures (approx. 800K) to achieve ignition and require much longer test times (up to 15 ms) to fully study the chemical kinetics and combustion chemistry of a reaction in a shock-tube experiment. Using mathematical models, analysis was performed studying the effects of temperature, pressure, shock-tube inner diameter, and test-port location at various test times (from 1 – 20 ms) on temperature maintenance. Three models, each more complex than the previous, were used to simulate test conditions in the endwall region behind the reflected shock wave with Ar and N2 as bath gases. Temperature profile, thermal BL thickness, and other parametric results are presented herein. It was observed that higher temperatures and lower pressures contributed to a thicker thermal boundary layer, as did shrinking inner diameter. Thus it was found that a test case such as 800K and 50 atm in a 16.2-cm-diameter shock tube in Argon maintained thermal integrity much better than other cases – pronounced by a thermal boundary layer < 1 mm thick and an average temperature > 799.9 K from 1–20 ms.
Show less - Date Issued
- 2007
- Identifier
- CFE0001593, ucf:47162
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001593
