Aerodynamic load maps of bluff bodies: Measurement and diagnostics

Abstract

Bluff bodies may assume arbitrary attitudes in a flow, causing aerodynamic loads that are sensitive to attitude. The Continuous rotation technique obtains 6-component loads on bluff bodies with 1-degree azimuth resolution about selected axes at a rate of 1 revolution per minute. The load coefficient variation is Fourier transformed and the resulting complex series is truncated in order to obtain rapidly computable, analytical formulae. The method is applied to bluff body shapes including cylinders, a cuboid, a flat plate and a porous box. A cylinder whose length is equal to its diameter, is used to show that rate effects, hysteresis, vortex shedding and other unsteady aerodynamic phenomena are negligible below 10 revolutions per minute. Approaches to generalize the aerodynamic loads on yawed finite cylinders of various aspect ratio are studied. The reasons for differences in aerodynamic load behavior between 2 cylinder models, are analyzed. To complement experiments, the ROTCFD unsteady Navier Stokes code is used to perform diagnostic computations. Methods to generalize the predictions are explored. Maps of the leading coefficients of the Fourier series of each load component over the aspect ratios space, are interpolated. The interpolation varies sharply for aspect ratios between 0.5 to 1. The variation is more gradual beyond aspect ratio 2. By aspect ratio 4, a ‘high aspect ratio’ limit appears to be reached.