Investigation Of The Blowoff Process And Characteristics In A Cavity-based Supersonic

In this dissertation,the lean-fuel combustion of gaseous fuel injected upstream of the cavity in the supersonic combustor was studied.The lean-fuel near-blowoff characteristics and the blowoff process were investigated numerically and experimentally.The lean-fuel characteristics of the flame with different injection schemes were analyzed by experiments and numerical simulations.The simulation results show that under the same injection pressure,fuel jets are closer to the cavity,fuel spanwise distributions are more uniform,more fuel are transported into cavities and the temperature in the cavity is higher in multiple-orifice cases.The lean-blowoff limits for the multiple-orifice cases are lower than that for the single-orifice cases.In single-orifice cases,the flamebases oscillate dramatically and the stability of the flame is poor.In multiple-orifice cases,the flamebases oscillate slightly at short distance downstream the cavity leading edge and the flame structure is stable.The effects of different total temperatures inflow and different fuels on the near-blowoff characteristics were studied by precise experimental methods.It is found that the flame is more stable with higher total temperature inflow under higher injection pressure.With the decrease of fuel injection pressure,the influence of different total temperature inflow on the flame structure and combustion flow field is reduced.Under the equivalent ratio near blowoff limits,different total temperatures inflow have little effect on the flame structure and the combustion flow field.Under the same injection pressure or the same equivalent ratio,the flame stability with hydrogen fuel is better,and the combustion intensity is larger,but the visible light intensity of the hydrogen flame is weaker.The larger the cavity is,the farther the flame is away from the cavity leading edge and the closer to the cavity trailing edge.The dynamic process of flame blowoff was observed by high-speed imaging camera,and the effects of different cavity sizes and different total temperatures inflow on the blowoff process were analyzed.The study found that the flame blowoff process can be divided into five parts:the shear-layer flame becomes weaker,the flame is partially extinguished near the trailing edge,the flame shrinks into the latter part of the cavity,the flame moves towards the cavity front wall and is subsequently extinguished completely.The effects of cavity size on the lean blowoff limits are nonlinear and the total temperature of inflow almost have no influence on the lean blowoff limits.The larger cavities have longer flame residence time in the cavity when the blowoff occur.The total temperatures of inflow have little effect on the blowoff process.