Measurements of fluctuating lift forces on rectangular cylinders in turbulent flow

Abstract

The fluctuating lift on a rectangular cylinder induced by turbulent flow is investigated by force measurement experiments. A square uniform grid is installed downstream of the entrance of the working section of the wind tunnel to generate approximately homogeneous and isotropic turbulence. The rectangular cylinder models of two different cross sections (width to depth ratio B/D = 5, 10) are tested in the experiments. Each rectangular cross section has two aspect ratios (length to width ratio θ = 1, 7) and a fixed width (B = 0.15 m). The measurements include the spectra of fluctuating lift force and vertical turbulent velocity component. From these measurements, the experimental values of generalized transfer functions of these rectangular cylinder models are obtained, which are compared with the calculated values based on three aerodynamic force theories. The one-wavenumber transfer functions and the spanwise influence terms of these rectangular cylinders are used in the calculations, which were determined by the pressure measurement experiments in the previous work. Comparisons of the measured and calculated values of generalized transfer functions demonstrate that the three-dimensional theory is satisfactory and confirm that the one-wavenumber transfer functions and spanwise influence terms determined by the pressure measurements are valid. The results also show that both the two-dimensional theory and the strip theory would overestimate the generalized transfer function, but for the rectangular cylinder with the larger aspect ratio, the strip theory is very close to the three-dimensional theory. The one-wavenumber transfer functions of these rectangular cylinders are therefore determined based on the strip theory. This indicates that the approximate approach to determination of the one-wavenumber transfer function, which was proposed for an airfoil in the previous work, could also be applicable to bluff bodies.