A Numerical Study on the Characteristics of Air–Fuel Mixing Using a Fluidic Oscillator in Supersonic Flow Fields

Abstract

In this study, numerical simulations were conducted to confirm the possibility of improved mixing performance by using a fluidic oscillator as a fuel injector. Three-dimensional URANS non-reacting simulations were conducted to examine air-fuel mixing in a supersonic flow field of Mach 3.38. The numerical methods were validated through simulations of the oscillating flow generated from the fluidic oscillator. The results show that the mass flow rate and momentum are reduced at the outlet because the total pressure loss increases inside the fluidic oscillator, which means that higher pressure needs to be applied to supply the same mass flow rate. The simulation showed that the flow structure varies over time as the injected flow is swept laterally. With lateral injection, the fuel distribution is long and narrow, and asymmetric vortexes are generated. However, with central injection, the fuel distribution is relatively similar to the case of using a simple injector. Compared to the simple injector, the penetration length, flammable area, and mixing efficiency were improved. However, the total pressure loss in the flow field increases as well. The results showed that the supersonic fluidic oscillator could be fully utilized as a means to enhance the mixing effect, however a method to reduce the total pressure loss is necessary for practical application.It is relatively easy to improve the mixing efficiency, but there is a disadvantage of significantly increasing the total pressure loss at a high Mach number. The cavity has been studied because it helps to mix the air-fuel and it can more effectively hold the flame in empty space where a recirculation zone can be formed on the wall [7][8][9][10][11][12][13][14]. A number of studies have been conducted on experiments or numerical simulations to observe the interaction of the cavity with flow fields in the combustion chamber [13] and derive the optimum cavity shape [7][8][9]. Recent studies have been conducted to find ways to improve the mixing performance through more diverse attempts, such as variable cavities and pylons and double cavities [10,11,14].Using the cavity, a scramjet engine can efficiently mix the air-fuel and hold the flame more easily with less total pressure loss. However, combustion instability can occur due to acoustic interference, and additional systems may be needed to compensate for this. A hyper-mixer is a system where a part of the wall of a combustion chamber has a form such as a ramp or a step. The shape generally induces a counter-rotating vortex, which helps to improve the mixing efficiency and expansion of the mixed area [15][16][17][18][19][20][21]. Studies have been carried out on adjusting the angle, arrangement, and shape of the injector [23-25] and using a swirler or counterflow nozzle [26,27].Unlike passive methods, active methods actively intervene in the flow of combustion chambers. Pulsed injection [28][29][30][31][32][33] and the Hartmann-Sprenger (H-S) tube [34,35] are examples of ways to directly affect the flow through variou...

Study of Arc Interruption Characteristics under Rated Current in Low Voltage Circuit Breakers

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