Towards isolated roughness induced boundary layer transition at supersonic speeds

González, Luis E. Mures; Dakka, Sam M

Abstract

The height of surface roughness elements affects the onset of laminar to turbulent transition in a boundary layer. CFD studies have been accomplished using RANS models at very low speeds, as a first step towards the understanding of this technology in supersonic/hypersonic flows. All simulations were performed on the commercial CFD program, ANSYS Fluent. Four flow cases have been investigated in this paper: natural transition of a 5.4 m/s flow over a flat plate, natural transition of a 9.8 m/s flow over a flat plate, implementation of a trip device in a 9.8 m/s flow and an attempt of capturing supersonic transition using a trip at Mach 3.5. Various turbulence models have been compared and the SST K-Omega gamma Transport model proved to capture the onset of transition with the best accuracy. The results concluded that a flow at 5.4 m/s naturally transitions 0.7 m downstream from the leading edge at 〖Re〗_x=2.59×10^5. Additionally, a 9.8 m/s flow transitions 1.25 m downstream at 〖Re〗_x=1.7×10^6. There is a difference of 0.55 m between these two values, highlighting the importance of roughness elements in high-speed flows. Both flows have been validated against experimental results from ERCOFTAC T3A and T3A- test cases. The implementation of a trip in the 9.8m/s flow moves the onset of transition further upstream. The critical height, in this case, is k⁄δ^* ≈ 0.25 and the effective height is 0.67<k⁄δ^* <0.68. Finally, an attempt to capture transition at Mach 3.5 using the same turbulence model did not achieve the desired results meaning other methods must be used in future work. With the limitations of physical testing capabilities for supersonic/hypersonic aerodynamics either due to the expense or unreliability of testing facilities, accurate CFD simulations of the effects of surface roughness are extremely important to contribute to ongoing research. There are many uses for this technology, ranging from commercial hypersonic flight to hypersonic missile systems.

Citation

González, L. E. M., & Dakka, S. M. (2024). Towards isolated roughness induced boundary layer transition at supersonic speeds. International Journal of Scientific and Technical Research in Engineering, 9(2), 1-16

• Journal Article Type: Article
• Acceptance Date: Apr 6, 2024
• Online Publication Date: Apr 6, 2024
• Publication Date: Apr 6, 2024
• Deposit Date: Jul 5, 2024
• Publicly Available Date: Jul 12, 2024
• Journal: International Journal of Scientific and Technical Research in Engineering
• Electronic ISSN: 2581-9941
• Peer Reviewed: Peer Reviewed
• Volume: 9
• Issue: 2
• Pages: 1-16
• Series ISSN: 2581-9941
• Keywords: Surface roughness element, boundary layer transition, ANSYS Fluent, CFD-Computational Fluid Dynamics.
• Public URL: https://nottingham-repository.worktribe.com/output/36876564
• Publisher URL: https://www.ijstre.com/Publish/9202024/754235703.pdf