Sensitivity of the damping controlled fluidelastic instability threshold to mass ratio, pitch ratio and Reynolds number in normal triangular arrays

Sensitivity of the damping controlled fluidelastic instability threshold of normal triangular tube arrays has been investigated through a theoretical-CFD hybrid methodology without the need for experimental data. The quasi-unsteady model with a theoretical model of the memory function was used to predict the critical velocity with the static fluid force coefficients obtained from steady RANS simulations. Five normal triangular tube arrays with pitch to diameter ratios of 1.25, 1.30, 1.32, 1.375 and 1.44 were investigated. Pressure on the tube surface for the P/d=1.32 array, predicted by the CFD, was compared with empirical measurements from the literature. Force coefficients obtained with the validated numerical model, were used to predict stability thresholds for the P/d=1.25 and P/d=1.375 tube arrays and the results were compared with previously published experimental critical velocities. The validated theoretical-CFD hybrid methodology was used to analyze and quantify the critical velocity specific dependence on three parameters: mass ratio, Reynolds number and pitch ratio. As expected, the pitch ratio has the most effect on the critical velocity. It was found that increased Reynolds number increases the stability threshold over the whole range of mass-damping parameters, but mass ratio has only a very minor effect, and this is confined to high mass-damping values.