Evolution of cellular structures on oblique detonation surfaces

Abstract

a b s t r a c tIn this study, numerical simulations using the inviscid Euler equations with one-step Arrhenius chemistry model are carried out to investigate the effects of activation energy and wedge angle on the stability of oblique detonation surfaces. Two kinds of cellular structure are studied, one is featured by a single group of transverse waves traveling upstream, referred to as LRTW (left-running transverse waves), and the other is featured by additional RRTW (right-running transverse waves). The present computational simulation reveals the formation of un-reacted gas pockets behind the cellular oblique detonation. Numerical smoked foil records are produced to show the emergence of the two types of transverse waves and the evolution of the unstable cellular structure of the oblique detonation. The transverse wave dynamics, including the colliding, emerging and splitting types, are found to be similar to the normal detonation propagation, demonstrating the instability mechanism is originated from the inherent instability of cellular detonations. Statistical analysis on the cellular structure is carried out to observe quantitatively the influences of activation energy and wedge angle. Results from the parametric study show that high activation energy and low wedge angle are favorable to the LRTW formation. However, the condition for the RRTW formation is more complex. In the case of low activation energy, small wedge angle is beneficial to the RRTW formation, as to the LRTW formation. In contrary, for high activation energy, there appears one moderate wedge angle favoring the RRTW formation and giving the shortest length between the onset of both LR and RR transverse waves. For quantitative comparison, we analyze the variation of two distances with the wedge angle, one is between the detonation initiation and LRTW formation points, and the other between LRTW and RRTW formation points. Results show the latter is relatively less pronounced than the former, indicating the RRTW formation depends mainly on the activation energy and the generation of LRTW.

Engine hot spots: Modes of auto-ignition and reaction propagation

“…(11), through the driving hot spot temperature gradient [6,20]. Higher values of E/R make oblique detonations more unstable, creating an irregular cellular structure [21]. …”

Numerical study of oblique detonation initiations with chain-branching kinetics

“…For the computation, the coordinate is rotated to the direction along the wedge surface. Hence, the Cartesian grid in the rectangular domain enclosed by the dashed line is aligned with the wedge surface, like our previous studies 6,7 .…”

“…For instance, Li et al 3 revealed that the multi-dimensional oblique detonation structure consists of a non-reactive oblique shock, an induction region, a set of deflagration waves, and an oblique detonation surface. The instability of oblique detonation surface has been studied widely, demonstrating the cellular structure formation and evolution 4,5,6,7 . Another research direction is the oblique shock-to-detonation transition, which can be viewed as the initiation process of oblique detonation.…”

The Effect of Chemical Reactivity on the Formation of Gaseous Oblique Detonation Waves

“…The pre-exponential constant for a given mixture k is used to define the spatial and temporal scales, so by solving the steady Zel'dovich-von Neumann-Döring (ZND), one-dimensional, Chapman-Jouguet (CJ) detonation, the half reaction zone length l 1/2 is unity [60,61]. Following previous studies, [62][63][64][65][66], the normalized heat release Q is chosen to be 50 and the isentropic exponent γ = 1.2. For the activation energy range considered in this work, i.e., E a = 5 to 60, k varies from 1.8 to 14,640.…”