This work aims at comparing the accuracy and overall performance of a low-Mach CFD solver and a fully-compressible CFD solver for direct numerical simulation (DNS) of nonequilibrium plasma assisted ignition (PAI) using a phenomenological model described in Castela et al. [1]. The phenomenological model describes the impact of nanosecond pulsed plasma discharges by introducing source terms in the reacting flow equations, instead of solving the detailed plasma kinetics at every time step of the discharge. Ultra-fast gas heating and dissociation ofO2 are attributed to the electronic excitation ofN2 and the subsequent quenching to ground state. This process is highly exothermic, and is responsible for dissociation of O2 to form O radicals; both of which promote faster ignition. Another relatively slower process of gas heating associated with vibrational-to-translational relaxation is also accounted for, by solving an additional vibrational energy transport equation. A fully-compressible CFD solver for high Mach (M>0.2) reacting flows, developed by extending the default rhoCentralFoam solver in OpenFOAM, is used to perform DNS of PAI in a 2D domain representing a cross section of a pin-to-pin plasma discharge configuration. The same case is also simulated using a low-Mach, pressure-based CFD solver, built by extending the default reactingFoam solver. Themore »
This content will become publicly available on April 1, 2023
On the Conservation of Turbulence Energy in Turbulence Transport Models
Abstract Zank et al. developed models describing the transport of low-frequency incompressible and nearly incompressible turbulence in inhomogeneous flows. The formalism was based on expressing the fluctuating variables in terms of the Elsässar variables and then taking “moments” subject to various closure hypotheses. The turbulence transport models are different according to whether the plasma beta regime is large, of order unity, or small. Here, we show explicitly that the three sets of turbulence transport models admit a conservation representation that resembles the well-known WKB transport equation for Alfvén wave energy density after introducing appropriate definitions of the “pressure” associated with the turbulent fluctuations. This includes introducing a distinct turbulent pressure tensor for 3D incompressible turbulence (the large plasma beta limit) and pressure tensors for quasi-2D and slab turbulence (the plasma beta order-unity or small regimes) that generalize the form of the WKB pressure tensor. Various limits of the different turbulent pressure tensors are discussed. However, the analogy between the conservation form of the turbulence transport models and the WKB model is not close for multiple reasons, including that the turbulence models express fully nonlinear physical processes unlike the strictly linear WKB description. The analysis presented here both serves as a more »
- Award ID(s):
- 1655280
- Publication Date:
- NSF-PAR ID:
- 10356041
- Journal Name:
- The Astrophysical Journal
- Volume:
- 928
- Issue:
- 2
- Page Range or eLocation-ID:
- 176
- ISSN:
- 0004-637X
- Sponsoring Org:
- National Science Foundation
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