Date of Award

9-25-2018

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Civil and Environmental Engineering

Keywords

CFD, Galloping, OpenFOAM

Supervisor

Cheng, Shaohong

Supervisor

Ting, David S-K.

Rights

info:eu-repo/semantics/openAccess

Abstract

Existing studies suggested a number of possible contributing factors to dry inclined cable galloping, including the axial flow forming on the leeward side of the inclined cable and the emergence of critical Reynolds number. The current study aims at investigating the role of cylinder orientation and Reynolds number in this phenomenon. A combination of the detached eddy and large eddy simulations was conducted to study the fluid structure around and aerodynamic force coefficients of a stationary circular cylinder normal to or inclined against the oncoming flow. The developed numerical models have been validated using existing numerical and experimental data. The effect of axial flow, in terms of the cylinder orientation represented by the attack angle (0 ◦ , 30 ◦ , 45 ◦ , 60 ◦ ), and the Reynolds number (3900, 1.4E4 , 1E5 , 1.4E5 , 2.8E5 ) have been discussed in detailed. A numerical study has been performed to indirectly examine the effect of the axial flow via a perforated splitter plate. Visualization of the fluid structure shows that a secondary flow forms on the leeward side of the circular cylinder when it is inclined, and the separated shear flow becomes more stable as cylinder orientation increases. Results indicate that the inclination of the circular cylinder would cause a near-zero span-wise averaged lift force due to the span-wise delay of the sectional cross-flow force coefficient. The sectional lift force coefficient is found to become more disorganized when the flow enters the critical Reynolds number régime in general. Within this critical range, the span-wise averaged lift force coefficient shows a peak amplitude that significantly differs from that in the subsequent shedding cycles when the attack angle is less than 45 ◦ . Results of the perforated splitter plate manifest that with the decrease of the splitter plate perforation ratio, a stronger interruption on the interaction between the two separated shear flows was found.

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