Accumulation of errors in numerical simulations of chemically reacting gas dynamics

Rotating detonation combustors and their similarities to rocket instabilities

Characterization of instabilities in a Rotating Detonation Combustor

Progress of continuously rotating detonation engines

A two-dimensional investigation is conducted to clarify the velocity decrease mechanism of a detonation wave propagating within a rotating detonation engine (RDE) chamber, focusing on the effect of injection conditions of the fuel and oxidizer. Two numerical studies are conducted; the first imitates the RDE chamber with injection ports in a rectangular computational domain, and the second simplifies the flow field in the RDE chamber based on observations of the first simulation. The injection is parameterized by the geometrical jet and the gas conditions (i.e., premixed or non-premixed). In the first simulation of the RDE chamber, the total length of the injection nozzles constitutes 20% of the length of the chamber's lower end. The number of nozzles, N, ranges from 10 to 500 under premixed and 25 and 125 under the non-premixed condition. As the nozzle interval increases, more burned gas exists in front of the detonation wave. Under the non-premixed condition for N = 25, the propagation velocity decreases to 84% of the CJ velocity, and 82.4% of the injected C2H4 is burned by the detonation. The CJ velocity is theoretically calculated, based on the amount of burned C2H4, to be 2283 m/s, which is not close to the propagation velocity of the simulation, 1999 m/s. In the simplified model in the second study, C2H4, O2, and burned gas are quiescently placed rather than injected, and the role of the upper wall is also examined. Significant velocity decrease, down to 86% of the CJ velocity, is observed when C2H4 and O2 are placed separately with a large width of burned gas between them. The amount of incompletely combusted C2H4 is inversely proportional to the propagation velocity except in the case with an upper wall. Therefore, burned gas has a larger effect on propagation velocity in the non-premixed condition.

Numerical investigation on detonation velocity in rotating detonation engine chamber

Numerical investigations of the restabilization of hydrogen–air rotating detonation engines

As the injection total pressure increases, the flow field in the combustion chamber of rotating detonation engine (RDE) becomes complicated and the detonation wave becomes unstable. When the total pressure is high enough, the detonation oscillates periodically and alternates between strong and weak. Under the same injection conditions, no oscillation is observed in two-wave RDE, and the two detonation waves propagate stably in the combustion chamber. The choking ratio of the injection Laval nozzle along the head end is not influenced by the total pressure, the mode of propagation, or the number of detonation waves. And thus the mass flux of RDE can be estimated using the maximum mass flux of the injection Laval nozzle. The specific impulse and thrust of RDE show overall growth as total pressure increases. However, they oscillate with the unstable detonation wave in one-wave RDE at high total pressure.

Numerical Investigation of the Stability of Rotating Detonation Engines

The structure of an oblique detonation wave (ODW) induced by a wedge is investigated via numerical simulations and Rankine–Hugoniot analysis. The two-dimensional Euler equations coupled with a two-step chemical reaction model are solved. In the numerical results, four configurations of the Chapman–Jouguet (CJ) ODW reflection (overall Mach reflection, Mach reflection, regular reflection, and non-reflection) are observed to take place sequentially as the inflow Mach number increases. According to the numerical and analytical results, the change of the CJ ODW reflection configuration results from the interaction among the ODW, the CJ ODW, and the centered expansion wave.

Structure of an oblique detonation wave induced by a wedge

The wedge-induced oblique detonation wave (ODW) at low inflow Mach number is investigated via Rankine–Hugoniot analysis and numerical simulations. The results show that the Chapman–Jouguet oblique detonation wave (CJ ODW) plays a significant role in the structure of the ODW. And the influence of the CJ ODW is the reason why an attached ODW can propagate upstream. Both the analytical and numerical results show that the decrease of inflow Mach number and the increase of wedge angle are conducive to the upstream propagation of ODW. In the upstream propagation process, a Mach reflection wave configuration is always established on the wedge surface. For the upstream propagating ODW that cannot detach from the wedge surface by itself, it will stabilize at a point on the wedge surface with an induction region, which is a few times the length of the induction zone of an ideal Zeldovich–von Neumann–Doring (ZND) detonation. Benefiting from the short induction region, the stabilized upstream propagating ODW has extr...

Analytical and Numerical Investigations of Wedge-Induced Oblique Detonation Waves at Low Inflow Mach Number

The particle path tracking method is proposed and used in two-dimensional (2D) and three-dimensional (3D) numerical simulations of continuously rotating detonation engines (CRDEs). This method is used to analyze the combustion and expansion processes of the fresh particles, and the thermodynamic cycle process of CRDE. In a 3D CRDE flow field, as the radius of the annulus increases, the no-injection area proportion increases, the non-detonation proportion decreases, and the detonation height decreases. The flow field parameters on the 3D mid annulus are different from in the 2D flow field under the same chamber size. The non-detonation proportion in the 3D flow field is less than in the 2D flow field. In the 2D and 3D CRDE, the paths of the flow particles have only a small fluctuation in the circumferential direction. The numerical thermodynamic cycle processes are qualitatively consistent with the three ideal cycle models, and they are right in between the ideal F—J cycle and ideal ZND cycle. The net mechanical work and thermal efficiency are slightly smaller in the 2D simulation than in the 3D simulation. In the 3D CRDE, as the radius of the annulus increases, the net mechanical work is almost constant, and the thermal efficiency increases. The numerical thermal efficiencies are larger than F—J cycle, and much smaller than ZND cycle.

Dan Wu

Papers

Numerical investigations of the restabilization of hydrogen–air rotating detonation engines

Numerical Investigation of the Stability of Rotating Detonation Engines

Structure of an oblique detonation wave induced by a wedge

Analytical and Numerical Investigations of Wedge-Induced Oblique Detonation Waves at Low Inflow Mach Number

Particle path tracking method in two- and three-dimensional continuously rotating detonation engines