Effect of inlet mass flow rate oscillation on simplex swirl injector flow based on VOF-to-DPM model

Abstract

The flow characteristics of injectors with oscillations play a significant role in the mechanism of combustion instability. And combustion instability reduces engine reliability. Therefore, an efficient VOF-to-DPM model-based method is proposed to evaluate the effect of inlet mass flow rate oscillation on the injectors in liquid rocket engines. In this method, the VOF-to-DPM model, which can portray the complete spray process with less computational cost than the VOF method, is adopted to simulate the whole spray process of the injector under oscillations. The proposed method is first verified by the reported simulation work. Then, it is applied to study the flow characteristics (response and spray characteristics) of the simplex swirl injector under different inlet mass flow rate oscillations. The result of the proposed method indicates that the simplex swirl injector is sensitive to the oscillation of 200–300 Hz, which is consistent with the reported experimental work. Additionally, inlet oscillation frequency dominantly increases the phase difference while frequency and amplitude jointly determine the amplification or attenuation of the outlet mass flow. The injector with 250 Hz has a higher velocity of downstream recirculation and smaller droplets than other oscillation frequencies, which may provoke combustion instability. The numerical results are beneficial to injector design and reduce the possibility of combustion instability by active regulation. The proposed method contributes to revealing the mechanism of combustion instability and improving the reliability of liquid rocket engines.