2D Reacting Flow
To cite the data:
Huang, C., Duraisamy, K., and Merkle, C.L., Investigations and Improvement of Robustness of Reduced-Order Models of Reacting Flow, AIAA Journal, 2019.
Swischuk, R., Kramer, B., Huang, C., and Willcox, K., Learning Physics-Based Reduced-Order Models for a Single-Injector Combustion Process , AIAA Journal, 2020.
McQuarrie, S. A., Huang, C., and Willcox, K., Data-driven reduced-order models via regularized operator inference for a single-injector combustion process, Journal of the Royal Society of New Zealand, 2021. (code available: https://github.com/Willcox-Research-Group/ROM-OpInf-Combustion-2D)
Description: A 2D planar representation of a generic laboratory-scale combustor  is established to assess the capabilities of ROMs for representing realistic combustion flowfields. The purpose of this dataset is to provide a testbed to build reduced models for relevant challenging reacting flow problems using different methods.
This simplified model allows ROM capabilities to be evaluated while maintaining the essential physics of interest. As shown below, the problem consists of a shear coaxial injector with an outer passage, T1, that introduces fuel near the downstream end of the inner passage and a coaxial center passage, T2, that feeds oxidizer to the combustion chamber. The T1 stream contains gaseous methane, whereas the T2 stream is 42% gaseous O2 and 58% gaseous H2O. Operating conditions are maintained similar to conditions in the laboratory combustor  with an adiabatic flame temperature of approximately 2700K and an imposed chamber pressure of 1.1 MPa. Both the T2 and T1 streams are fed with constant mass flow rates: 5.0 and 0.37 kg∕s, respectively. A non-reflective boundary condition is imposed at the downstream end to control acoustic effects on the combustion dynamics. For all the cases in the current paper, a 10% sinusoidal perturbation at 5000 Hz is imposed at the downstream boundary to generate coherent dynamics. Combustion is represented by the single-step global model of Westbrook and Dryer ,
CH4 + 2O2 → CO2 + 2H2O
As reported in Ref. , stable, accurate reconstruction of CFD solutions of flows with stiff chemistry is highly challenging. To diminish these difficulties, the present simulations are based on a reduced pre-exponential factor, which is a factor of 10 smaller than the value in  and corresponds to a characteristic chemical time scale of approximately 0.8 μs and a laminar flame thickness of approximately 1 mm. The FOM was calculated using a constant time step at 0.1 μs and unstructured mesh with grid size, 0.18 mm, in the reacting regions. Even with this reduced reaction rate, the resulting ROMs remain highly temperamental and provide a clear example of the additional difficulties engendered when reactions are present. This reduced reaction rate provides conditions more favorable for ROM development than the original stiff value while maintaining representative flame dynamics in the combustor. A representative animation of the reacting FOM solutions is shown below to demonstrate the overall character of the flowfield and to highlight the dominant physics in the problem of interest. The combustion dynamics are characterized by highly dispersed pockets of intense heat release that are intermittently distributed in both space and time. The temperature and heat-release contours span a wide range of scales from the small eddies in the shear layers to the large-scale recirculation zone behind the dump plane. All these unique features introduce varying levels of difficulty in constructing a robust ROM.
1. Yu, Y., Sisco, J. C., Rosen, S., Madhav, A., and Anderson, W. E., “Spontaneous Longitudinal Combustion Instability in a Continuously-Variable Resonance Combustor,” Journal of Propulsion and Power, Vol. 28, No. 5, 2012, pp. 876–887. https://doi.org/10.2514/1.B34308
2. Westbrook, C. K., and Dryer, F. L., “Simplified Reaction Mechanisms for the Oxidation of Hydrocarbon Fuels in Flames,” Combustion Science and Technology, Vol. 27, Nos. 1–2, 2007, pp. 31–43. https://doi.org/10.1080/00102208108946970
3. Huang, C., Xu, J., Duraisamy, K., and Merkle, C., “Exploration of Reduced-Order Models for Rocket Combustion Applications,” AIAA SciTech Forum 2018, AIAA Paper 2018-1183, 2018. https://doi.org/10.2514/6.2018-1183