Lee, Kah Kheng
(2021)
Supersonic Turbulent Flow Modelling Over Steps And Cavities.
Project Report.
Universiti Sains Malaysia, Pusat Pengajian Kejuruteraan Aeroangkasa.
(Submitted)
Abstract
Altitude compensating nozzles provide ideal conditions for propulsion, ignoring the effect of atmospheric pressure that will cause the reduction of efficiency. Past experiments discovered the effect of fuel combustion on the surface of nozzles, which causes cross-hatching patterns on the wall due to enthalpy, known as ablation. Cross-hatching patterns act as surface roughness that causes flow disturbance to the supersonic flow field within the nozzle. A numerical experiment is conducted to examine the supersonic turbulent flow behaviour over cross-hatching relief surfaces in order of steps and cavities with different length-to-depth ratios(L/D), including the induced drag as the direct physical effect of flow losses. After getting the fundamental concepts, the numerical experiment setup is started with reviewing the assumptions and limitations, which will be further applied in the simulation afterwards. 2D-modelling is done with Solidworks, following by the meshing in Pointwise. The simulation result from Ansys Fluent is further interpreted and presented with Techplot in the form of graph and contour. The numerical experiment is a parametric study which is 150% to the reference paper, with 14 variants of length-to-depth ratios in the range of 4.17 to 17.21. For closed cavity type flow (15.39 ≤ L/D ≤ 22.99), it yielded larger drag force due to the separation shock found which increased linearly with smaller L/D ratio. The drag force decreased drastically for transition cavity type flow (L/D = 13.23) as less flow separation was formed. For open cavity type flow (4.17 ≤ L/D ≤ 11.61), it yielded small drag force as shear layer was completely formed above the cavity with large recirculation regions inside the cavity.
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