Investigation Of Validation, Modeling And Application Of Flamelet Model In Supersonic Turbulent Combustion

The present research investigates the supersonic combustion in a scramjet combustor and develops a new flamelet model for supersonic combustion. The new flamelet model was implemented based on the in-house hybrid LES/RANS code and validated by experimental investigations.Firstly, flamelet model for turbulent combustion in low-speed flow was introduced based on basic theory of flamlet for laminar flow, then it was extended to supersonic flow and revised according to compressibility and occurrence of shock waves in flow field. A steady flamelet model for supersonic turbulent combustion was established, and it takes into account the effects of shock waves.Secondly, whether the flamelet model is feasible for the supersonic combustion flow field is analyzed by distinguishing whether the supersonic combustion flow field in a scramjet combustor meets the assumptions of flamelet model. The results show that: (i) for premixed combustion, as the fluctuation velocity of the flow in low-speed recirculation zone and mixing layer is very slow, the entire flow field will satisfy the assumption of flamelet model at all flight Mach numbers, (ii) for non-premixed combustion, most parts of the flow field satisfy the assumption of flamelet model and only a small part of the flow field at high flight Mach number does not meet.Thirdly, the processing methods of the steady flamelet model in the vicinity of the critical scalar dissipation rate may result in a discontinuity of the solution. Further, this discontinuity can introduce non-physical solutions and numerical instabilities. Based on the flamelet/progress variable model for the low-speed flows, a new flamelet/progress variable model which takes into account the effect of the shock waves was established. In the meantime, an efficient method for the generation of flamelet data libraries was developed.Finally, in order to validate the applicability of the new flamelet/progress variable model to simulate the supersonic combustion flow field with complex configurations, the supersonic flow and combustion of the scramjet combustors with strut and cavity configurations were investigated through both experimental investigations and numerical simulations. The results indicate that the new developed flamelet/progress variable model is capable of describing the fluid flow and combustion in a scramjet combustor with complex configurations. When the strut thickness and the ER of the fuel change, the response of the combustion efficiency was quantificationally investigated, and the results reveal that the strut thickness and the ER of the injected fuel have little effect on the combustion efficiency. Through the quantificational studies, the influence of the injection angle and ER of the fuel, and the multi-cavity configuration on the combustion efficiency were revealed. The results show: (i) the combustion efficiency is higher when the fuel is injected in a vertical direction than in any other direction, (ii) an increase in the ER has little effect on the combustion efficiency, (iii) cavities installed in tandem can increase the combustion efficiency, (iv) when the fuel is injected from one side of the combustor walls, the cavities installed in parallel have little effect on the combustion efficiency but increase the loss of total pressure, and (v) when the fuel is injected from both sides of the combustor walls, cavities installed in parallel will greatly increase the combustion efficiency.