This report has as its objective the investigation of the aerodynamic effects resulting from a modification of the surface perturbation patterns of overhead conductors widely employed to transmit high voltage electricity over long distances of terrain. Conductor cables are particularly susceptible to the fatigue failure induced by repeated cycles of bending stress arising from uncontrolled vibration. Although the installation of such suppression devices as Stockbridge-type dampers can successfully mitigate these deleterious effects, a cost-effective and simple solution emanating from a thorough physical understanding of the behaviour of air over these bluff bodies is the most desirable solution. A purely numerical approach is taken to simulate the uniform flow of air over idealised sections of computer generated cylinders featuring differing surface geometry patterns in the endeavour of identifying the optimal combination of the values of key surface feature parameters which result in the greatest mitigation of aerodynamic forces and susceptibility to Aeolian vibration. Fundamental aspects related to the generation of the two-dimensional computational domain and the running of the simulation such as the appropriate discretisation scheme to be employed, the choice of turbulence model, near-wall grid refinement, and boundary and initial conditions are described in considerable detail.

Prior to this parametric investigation, the accuracy of the numerical scheme and the credibility of the results produced by the numerical software package must be assessed. To this end, a systematic validation and verification procedure is implemented. Three computational grids of varying density and two differing time steps will be compared for their convergence in predicting the values and profiles of mean flow parameters along the surface of the cylinder and in the wake. Additionally, to establish the credibility of the results produced by the Computational Fluid Dynamics (CFD) computer program, ANSYS Fluent, comparison will be made to the results obtained by experimental and highly accurate numerical studies conducted on the well documented case of the uniform flow over a stationary cylinder at a Reynolds number of 3900. The work described in this paragraph and the one to follow is beyond the scope of the current report.

Having established the accuracy of the numerical model, a three-dimensional domain will then be created for the purpose of performing the parametric study. Such surface feature parameters as helix angle, strand thickness, groove width and pattern orientation will be modified in the attempt to identify the unique combination of factors which result in the greatest reduction of the aerodynamic forces and provide the best control of the near wake flow. However, the appropriate spanwise length of the resultant cable for which three dimensional flow structures can be witnessed in the wake must first be identified; this is due to the fact that at the Reynolds number range considered, i.e. the sub-critical regime, turbulence structures materialise in the shear layers and in the near wake flow. To aid in the identification of the aerodynamic effects induced by a modification of the values of key surface feature parameters, an analysis of the following mean and instantaneous flow parameters will be made:

• Temporal histories of the drag and RMS lift;
• Pressure coefficient distribution along the bluff body and its evolution in the wake;
• U-velocity at various streamwise stations;
• Frequency domain analysis of u- and v-velocity fluctuations; and
• Flow visualisation using contours of vorticity magnitude.

Additionally, the synchronisation condition will be simulated in an assessment of the degree of control of the near wake flow achieved by the differing models. To predict the transverse displacement of the structure in response to the unsteady fluid loading imposed on the cylindrical structure by the flow, a user defined function will be developed.