Abstract
This paper presents an experimental study on rotating detonations in a hollow combustor with the slit-orifice nozzle. The experimental results reveal that the propagation speed of detonation waves increases with the rise of mass flow rates and is greater than the Chapman–Jouguet detonation speed (VC−J). Furthermore, numerical simulations of rotating detonation in a non-premixed three-dimensional cylindrical combustor have been conducted based on a multispecies reacting code. The influence of two mixing schemes—that is, slit-orifice and coaxial injector—on detonation waves are studied to determine whether the characteristics of detonation waves tend toward high-frequency combustion instability due to changes in the mixing scheme. It is found that the slit-orifice scheme’s detonation speed, pressure, and temperature are significantly higher than those of the coaxial injector scheme. In particular, the detonation speed of the former reaches 124% of the VC−J, while that of the latter is only 80.5% of the theoretical value. The numerical results reveal that the low-speed detonation is caused by the deterioration of the hydrogen (H2)/air mixing conditions. Moreover, the flow-field structures of two mixing schemes were comparable, both containing transverse detonation waves, oblique shocks, contact surfaces, and wedge-shaped reactant regions. Furthermore, the Rayleigh index analysis showed that the unsteady heat release was in phase with the pressure fluctuations, amplifying the pressure. Therefore, it is suggested that high-frequency combustion instability may be a manifestation of rotating detonation waves under poor mixing conditions.
Highlights
The combustion instability of liquid rocket engines (LREs) was discovered in the 1930s,1 and it has since been regarded as a risk factor in developing high-thrust rocket engines
The results showed that an increase in the mass flow rate of the injectors near the wall led to an increase in the amplitude of the tangential combustion instability
Because the slit-orifice nozzle and coaxial injector are the injection modes commonly used in rotating detonation experiments and LREs, studying the propagation characteristics of detonation waves under these two injection methods helps reveal the relationship between detonation and combustion instability
Summary
The combustion instability of liquid rocket engines (LREs) was discovered in the 1930s,1 and it has since been regarded as a risk factor in developing high-thrust rocket engines. Droplet evaporation has been widely studied as an important incentive factor for combustion instability.. The combustion process of gaseous propellants shows similar instability phenomena.. Flandro et al. believed that a view based purely on acoustic waves was a distortion of experimental phenomena. These classical theories ignore the fact that shock waves have been observed in violent combustion instability experiments. Researchers called shock waves that appeared in high-frequency combustion instability “detonation-like,”18–22—that is, as a typical
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