Effects of inlet bend geometry on flow distortion and combustion performance in a solid rocket ramjet

Authors:
  • PCPengxin Chen
    Pengxin Chen
  • ZWZhiwen Wu
    Zhiwen Wu
  • XZXinhao Zhao
    Xinhao Zhao
  • YZYiqiao Zhang
    Yiqiao Zhang
  • YWYifan Wu
    Yifan Wu
  • TLTianyu Lu
    Tianyu Lu
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Abstract
The geometric configuration of a side-mounted inlet bend plays a crucial role in determining the outlet flow quality of the inlet duct and the mixing combustion organization within the afterburner of a solid rocket ramjet. In this study, three-dimensional numerical simulations were conducted to investigate the effects of bend length, turning angle, and expansion ratio on the flow characteristics at the inlet bend exit and the subsequent air/primary-gas combustion process. The coupled mechanisms by which bend geometric parameters affect flow distortion, total pressure recovery, and mixing–combustion organization were elucidated. Results indicate that under cold-flow conditions, the outlet flow quality is governed by the combined effects of centrifugal forces, pressure gradients between the inner and outer bend walls, and the evolution of Dean secondary flow structures. Larger bend lengths and expansion ratios tend to intensify low-momentum fluid accumulation and aggravate total pressure distortion, whereas variations in turning angle primarily modify transverse pressure redistribution and secondary flow transport pathways, without exhibiting a clear monotonic trend. Under reacting conditions, heat release and gas expansion significantly reconstruct the pressure field and secondary flow structures within the bend, suppressing large-scale Dean vortices and substantially improving total pressure recovery. However, the influence of geometric parameters differs markedly from that observed under cold-flow conditions. Moderate bend lengths and expansion ratios provide a more favorable compromise between pressure recovery, flow uniformity, and combustion stability. Increasing the turning angle enhances transverse transport and turbulent mixing, thereby promoting combustion efficiency, albeit at the cost of additional aerodynamic losses. Although excessively small expansion ratios facilitate rapid near-field mixing, they weaken the transverse redistribution capability required to mitigate thermally induced pressure non-uniformities, resulting in localized high-pressure cores and increased outlet flow distortion after combustion. Overall, the geometric parameters of the inlet bend exert a significant influence on the outlet flow quality and its coupling with combustion organization. Proper geometric optimization can effectively improve the integrated aerodynamic and combustion performance of solid rocket ramjet engines.

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