Effects of cavity shapes and sizes on rarefied hypersonic flows

• Published in: International journal of mechanical sciences 2023-05, Vol.245, p.108088, Article 108088
• Main Authors: Jiang, Qihan, Cai, Guobiao, Chen, Yatao, Yuan, Junya, He, Bijiao, Liu, Lihui
• Format: Article
• Language: English
• Subjects: Cavity; Cavity shape; Cavity size; Hypersonic vehicle; Rarefied hypersonic flow
• ISSN: 0020-7403; 1879-2162
• DOI: 10.1016/j.ijmecsci.2022.108088

Cavity structures are frequently encountered on hypersonic vehicle surfaces, which change the aerodynamic heat flux and force (pressure) compared with flat vehicle surfaces. The effects of the cavity length-to-depth ratio, cavity rounded corners, Maxwellian accommodation coefficient, and free-stream Knudsen number on the heat flux and pressure loaded on the vehicle surface with rectangular cavities have been studied extensively. Still, the influence of the cavity shape and size remains. In this study, the effects of cavity shape and size on the flow field characteristics and aerodynamic surface quantities on the surface are analyzed using the direct simulation Monte Carlo method. The rectangular cavities with sidewall angles (α) of 0°, 15°, 30°, and 45° are selected to investigate the shape influence, and the semicircular cavities with radii (R) of 3, 6, 9, and 12 mm are chosen for size effect. The results indicate that the gas flows over the cavity configurations specified in our study hold the “open-cavity” characteristics. The vortexes formed inside the cavity are shrunk as α increases from 0° and 45°, but they are similar under the R-range explored. The pressure, skin friction, and heat transfer coefficients over the surface display complex trends as varying α and R. In addition, the effect of cavities on the overall aerodynamic heat flux and force, which are vital for practical applications, are explored. The results reveal that the aerodynamic heat flux is dramatically influenced by α and R, while the aerodynamic force is mildly affected. Overall, the larger the α and R, the greater the effect of the cavity on the rarefied hypersonic flows. Our research is beneficial to the protection and optimal design of hypersonic vehicles. [Display omitted] •Cavity shape and size effects on rarefied hypersonic flow are studied numerically.•Cavities with different sidewall angles (α) and radii (R) are utilized.•The gas flows over the cavity explored hold the open-cavity characteristic.•The effect of cavities on the overall aerodynamic heat flux and forces is explored.•The larger the α and R, the greater the cavity effect on rarefied hypersonic flows.