Flamelet-like models applied in scramjet combustors: A state of art and prospect

Developing supersonic combustion models with efficiency, accuracy and practicality is important foundation to deeply understand the complex combustion processes in scramjet engines. Characterized by efficiency and intuition, the flamelet-like models are widely used models in computational combustion methods. However, the supersonic combustion flow field has the nature of strong compressibility, multiple modality, and multiple scales, which poses a great challenge to the traditional flamelet-like models with fixed boundary conditions, and then the complex chemical reaction mechanisms that may face will impose additional computational burden. In this context, this paper reviews the flamelet-like models used in scramjet engines, and summarizes prominent issues in the application practice, including modeling partially premixed combustion, defining progress variable, solving temperature efficiently, evaluating assumed Probability Density Function (PDF) models, and treating mixture fraction variance. Furthermore, possible prospects and directions of improvements are proposed and highlighted for the flamelet-like models. To fully describe the physicochemical scenario and address the raised challenges, these improvements are dedicated to dealing with the compressibility, temperature rise, time-scales, species of interest, multi-inlet combustion, the progress variable definition, and the higher Mach number flight condition.