Towards predicting dry cable galloping using detached eddy simulation

Abstract

<p>A computational approach based on a k-ω delayed detached eddy simulation (DDES) model for predicting aerodynamic loads on a smooth circular cylinder (cable) is verified against experiments. Comparisons against preexisting data are performed for a static cylinder where the flow is normal to the cylinder axis. New experiments are conducted where the cylinder axis is inclined with respect to the inflow velocity at the desired yaw angle, β=30à  à °. The experimental setup is described and the measurement data is used for code verification. Verification results are presented for two inflow angles, β=0à  à ° and 30à  à °. Comparisons with data include distributions over the cylinder surface of mean and rms of pressure coefficient, mean wake velocity profiles behind the cylinder, and power spectra of sectional lift coefficient.</p> <p>Simulations are conducted for two general categories - (1) laminar separation, when the laminar boundary layer on the cylinder separates and transition to turbulence occurs in the shear layer, and (2) turbulent separation, when the boundary layer naturally transitions to turbulent, and then the turbulent boundary layer separates. For the laminar separation cases, agreement of predictions with measurements is good for mean and rms surface pressure and wake velocity deficit; the lift spectrum prediction however shows a slight offset in frequency. Very limited experimental data is available in the turbulent separation category.</p> <p>The results of the three yawed flow cases (β=15à  à °, 30à  à °, 45à  à °) found to be independent of β (dynamic scaling) when the flow speed normal to the cylinder axis is selected as the reference velocity scale. This 'independence' is observed when the category of flow separation does not change with β. Spatio-temporal plots of instantaneous sectional lift and drag for yawed flow simulations clearly show presence of spanwise flow.</p> <p>Finally, the capability of the solver to perform dynamic simulations is demonstrated for two canonical, prescribed cylinder motions - transverse and horizontal harmonic oscillations for a given frequency and amplitude. The mean and unsteady loads on the cylinder are found to vary drastically with cylinder motion. The results and verification with experiments presented here demonstrate the capability of the computational methodology to accurately predict aerodynamic loading on cables. Accurate load prediction is a critical element in aeroelastic models that are required to predict dry cable galloping.</p>