Lim, Wei Fong
(2021)
Supersonic Turbulent Flow Modelling Over Large Amplitude-To-Wavelength Periodic Wavy Surfaces.
Project Report.
Universiti Sains Malaysia, Pusat Pengajian Kejuruteraan Aeroangkasa.
(Submitted)
Abstract
Due to ablation by the high enthalpy flow accelerated by the nozzle, various surface roughness patterns are formed on the post ablated inner wall's surface of the nozzle. These surface roughness patterns will induce disturbances to the supersonic flow and may lead to flow separation, which contributes to the rise of the total drag, followed by reduced thrust output. In the present study, the surface roughness pattern focused is the cross-hatched pattern, which is modelled into a simplified 2-D model of roughness elements in the form of periodically repeating wavy surfaces by using SolidWorks. A numerical experiment is conducted by using ANSYS Fluent to investigate the effect of a larger amplitude-to-wavelength ratio of wavy wall surface on the flow field properties and corresponding drag induced. Moreover, to study the characteristics of the supersonic flow field over a 2-D periodic wavy surface under overexpanded flow conditions using CFD. Parameter to be manipulated for different amplitude-to-wavelength ratios is the surface wavelengths and keeping the wave amplitudes constant at 0.375 mm. The steady-state simulations will be run for 14 variants with amplitude-to-wavelength ratios of wavy surfaces (0.008-0.057) under overexpanded conditions and a freestream Mach number of 3.2 by using k-omega SST turbulence model. The number of oblique shock waves and expansion waves is found to increase with the decreasing of surface wavelengths in the general flow features. Due to the presence of the shockwaves in all cases, the total drag force is always pressure-dominated, and the pressure contribution increases with the substantial reduction of surface wavelengths.
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