Parametric design and analysis of modular-to-annular rocket-based combined cycle engine supersonic turning isolator

The isolator, as a critical component connecting the inlet and combustor, plays a vital role in enhancing overall engine performance. Given the geometric complexity of three-dimensional isolators and their intricate internal flow characteristics, design methodologies and flow field structures for these isolators require further investigation. This study focuses on the modular-to-annular rocket-based combined cycle (RBCC) engine isolator and proposes a parametric modeling approach based on the “spine curve + rib curve” concept. This method decouples three critical design factors, including flow turning, cross-sectional transition, and streamwise area variation, enabling independent control through corresponding parameters. Numerical simulations were conducted to investigate the effects of different turning patterns and cross-sectional transition laws on isolator performance and flow field structures. Results indicate that turning patterns considerably influence isolator performance. The moderate turning configuration demonstrates no significant flow separation, achieving an optimal total pressure recovery coefficient of 0.653, while the sharp-to-gradual turning configuration shows the poorest performance with a total pressure recovery coefficient of only 0.421. Since high backpressure primarily affects the downstream portion of the isolator, creating a large subsonic region, the gradual-to-sharp turning configuration exhibits the best anti-backpressure capability. In contrast, different cross-sectional transition patterns have minimal impact on performance, with total pressure recovery coefficients varying by less than 2% and nearly identical anti-backpressure performance. Finally, an aerodynamic optimization platform was developed. The optimization yielded an isolator configuration achieving a total pressure recovery coefficient of 0.656, with no significant flow separation observed in the flow field and a stable supersonic core flow.