Modeling the unsteady forces on a finite-length circular cylinder in cross-flow

Abstract

Semi-empirical models, for unsteady lift, drag, and axial forces, are developed to predict the spectral features of the unsteady forces on a finite-length, right circular cylinder in cross-flow. In general, the models consist of two parts; the spatial variation of rms wall pressure on the cylinder, and the correlation lengths, or areas, which describe the spatial extent of the correlation of the unsteady pressures. Experiments were conducted in a low-noise wind tunnel to measure the statistics of the unsteady wall pressures on a model cylinder. The results from the measurements are incorporated into the theoretical models, and predictions are made for the spectral characteristics of the theoretical lift, drag, and axial forces. The unsteady lift and drag predictions using the models developed in this work agree well with previously measured unsteady force data measured on gradient hyrdophones exposed to flow. Below St=0.8 the unsteady lift and drag are found to be the dominant force on the cylinder, while above St=0.8 the unsteady axial force dominates.