A computational study of the interaction of gaseous detonations with a compressible layer

Abstract

The propagation of two-dimensional cellular gaseous detonation bounded by an inert layer is examined via computational simulations. The analysis is based on the high-order integration of the reactive Euler equations with a one-step irreversible reaction. To assess whether the cellular instabilities have a significant influence on a detonation yielding confinement, we achieved numerical simulations for several mixtures from very stable to mildly unstable. The cell regularity was controlled through the value of the activation energy, while keeping constant the ideal Zel’dovich - von Neumann - Döring (ZND) half-reaction length. For stable detonations, the detonation velocity deficit and structure are in accordance with the generalized ZND model, which incorporates the losses due to the front curvature. The deviation with this laminar solution is clear as the activation energy is more significant, increasing the flow field complexity, the variations of the detonation velocity, and the transverse wave strength. The chemical length scale gets thicker, as well as the hydrodynamic thickness. The sonic location is delayed due to the presence of hydrodynamic fluctuations, for which the intensity is increased with the activation energy as well as with the losses to a lesser extent. The flow field has been studied through numerical soot foils, detonation velocities, and 2D detonation front profiles, which are consistent with experimental findings. The velocity deficit increases with the cell irregularity. Moreover, the relation between the detonation limits obtained numerically and in detonation experiments with losses is discussed.

Effect of incident laser sheet orientation on the OH-PLIF imaging of detonations

“…The unsteady 2-D simulations were performed using an inviscid formulation with detailed chemistry. Particulars about the numerical methods used, spatial and temporal discretizations as well as the parallelization methodology can be found in [16]. Briefly, we used time-operator splitting to couple the hydrodynamics to the chemistry together with directional splitting, along with a ninth-order monotonicity preserving interpolation in space, and a third order explicit Runge-Kutta in time.…”

Dynamics of detonations with a constant mean flow divergence

“…Instead, the rapid burn-out of non-reacted pockets by diffusive processes explains why the reaction zones remain substantially shorter. The effective reaction rates for the dynamics of cellular detonations extracted from these experiments can naturally find use in problems in which quasi-steady and stationary cellular detonation waves appear, for example in problems of detonations weakly confined by an inert layer (Reynaud et al 2017) as for rotating detonation engines. Future work should be devoted to this validation.…”

“…In gases, real detonations are multi-dimensional and their reaction zone is often turbulent; deviations from the ZND model are substantial (Lee 2008;Shepherd 2009) and cannot be treated as perturbations. Analysis of unstable detonations revealed that although the structure is highly transient, it recovers qualita-tively a quasi-one-dimensional average structure analogous to the ZND structure, with an average sonic surface (Gamezo et al 1999;Radulescu et al 2007b;Reynaud et al 2017;Maxwell et al 2017). It thus appears that, with the appropriate kinetic description for the averaged fluid state and speed dictated by an effective rate of energy release, the ZND model with its extensions may be an appropriate framework to model real detonations at the macro-scale.…”

“…Paradoxially and controversially, the role of cellular structures in numerically calculated inviscid detonations with mass divergence (solved with the Euler equations) has been shown to make the detonations more difficult to ignite than predicted from models derived from a laminar structure (Radulescu et al 2007a;Han et al 2017b,a). Inviscid cellular detonations were found to be more prone to failure in weakly confined charges (Reynaud et al 2017) and in the analogous problem of porous walled tubes (Mazaheri et al 2015). The authors found pockets of non-reacted gas that delay the global exothermicity.…”

Mechanism of end-gas autoignition induced by flame-pressure interactions in confined space

“…Flame propagation and deflagration-to-detonation transition (DDT) have drawn extensive attention over the past years not only due to their destructive effects in the fire safety area such as mine explosion but also because of their potential applications in some propulsion systems, e.g., a pulsed detonation engine (PDE). [1][2][3][4][5][6][7][8] It is generally considered that the overall DDT process in a smooth tube basically involves three stages: first, flame acceleration and leading shock wave generation, then formation of the preheated zone ahead of the flame front, and finally, formation of a detonation wave (DW). 8,9 However, the quantitative theory and comprehensive mechanism of DDT remain still poorly understood as a result of its complicated combination of multiple highly nonlinear processes including interactions among flames, shocks, boundary layers, and turbulence.…”