Diffusion and mixing effects in hot jet initiation and propagation of hydrogen detonations

Abstract

In the present work, the role of diffusion and mixing in hot jet initiation and detonation propagation in a supersonic combustible hydrogen–oxygen mixture is investigated in a two-dimensional channel. A second-order accurate finite volume method solver combined with an adaptive mesh refinement method is deployed for both the reactive Euler and Navier–Stokes equations in combination with a one-step and two-species reaction model. The results show that the small-scale vortices resulting from the Kelvin–Helmholtz instability enhance the reactant consumption in the inviscid result through the mixing. However, the suppression of the growth of the Kelvin–Helmholtz instability and the subsequent formation of small-scale vortices imposed by the diffusion in the viscous case can result in the reduction of the mixing rate, hence slowing the consumption of the reactant. After full initiation in the whole channel, the mixing becomes insufficient to facilitate the reactant consumption. This applies to both the inviscid and viscous cases and is due to the absence of the unburned reactant far away from the detonation front. Nonetheless, the stronger diffusion effect in the Navier–Stokes results can contribute more significantly to the reactant consumption closely behind the detonation front. However, further downstream the mixing is expected to be stronger, which eventually results in a stronger viscous detonation than the corresponding inviscid one. At high grid resolutions it is vital to correctly consider physical viscosity to suppress intrinsic instabilities in the detonation front, which can also result in the generation of less triple points even with a larger overdrive degree. Numerical viscosity was minimized to such an extent that inviscid results remained intrinsically unstable while asymptotically converged results were only obtained when the Navier–Stokes model was applied, indicating that solving the reactive Navier–Stokes equations is expected to give more correct descriptions of detonations.

Dynamic detonation stabilization in supersonic expanding channels

“…The highest grid resolution in Case 2 of min Δ =7.8×10 -6 m, which corresponds to 275 Pts/Lhr (points per half reaction length), has been effectively verified in recent works [4,10]. It is reported that the viscous scale is the smallest among the three diffusive scales (viscous shear layer, thermal heat conduction layer and mass diffusion layer).…”

“…It has been demonstrated that in straight channels overdriven detonation can attenuate to CJ detonation and dynamically stable propagation of detonation can be achieved when the supersonic incoming flow is given the corresponding CJ velocity after the shutdown of the hot jet [4]. Different from straight channels, the product in expanding channels is expected to expand more freely due to the Prandtl-Meyer expansion, which is theoretically able to result in further attenuation of CJ detonation and even detonation failure.…”

“…Based on the idea of a detonation-driven scramjet (DDS), a series of numerical and experimental investigations have been conducted on detonation combustion in supersonic combustible mixtures of both simplified straight channels [3][4][5], which mainly concentrate on detonation initiation and its propagation characteristics in supersonic combustible mixtures, and cavity-based straight channels [6] focusing on detonation stabilization owing to cavity oscillations [7][8][9].…”

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

“…With the adaptive mesh refinement method, AMROC can accurately resolve the flame front, shock wave, and detonation, and thus has been successfully applied to the extensive studies of combustion. 53,[58][59][60][61][62]…”

Detonation Stabilization in Supersonic Flow: Effects of Suction Boundaries

“…The present work uses the NS equations with the one-step chemistry model as governing equations [23]. Currently, it is very expensive to conduct high-resolution multidimensional detonation simulations solving the NS equations with detailed chemistry.…”