Aerodynamic characteristics of axial circular cylinders with low fineness ratios between 0.5 and 0.75 using a magnetic suspension and balance system

In this study, aerodynamic force and flow field of an axial circular cylinder with a low fineness ratio parallel to an airflow were investigated using the 1.0-m magnetic suspension and balance system (MSBS). The models with fineness ratios of 0.5 to 0.75 were tested in the support-interference-free condition at Reynolds numbers from 0.8×10⁵ to 1.4×10⁵. The aerodynamic force was measured by the MSBS and the base pressure was obtained by a wireless pressure-measurement device. The flow field was visualized by a smoke wire method. The results of force measurement show that the drag decreases monotonically in the range of fineness ratio larger than 0.5. This means that the critical geometry, at which the fineness ratio shows the local maximum of the drag coefficient, does not exist in the region of the fineness ratio larger than 0.5. The base pressure coefficient shows the tendency similar to the drag coefficient. This also indicates that there is no possible existence of the critical geometry. The fluctuating aerodynamic force in the lateral and vertical directions is larger than that in the axial direction. The visualization show that the flow separated from the leading edge generates transverse vortices and the recirculation area is formed close behind the model. The wake in the downstream is highly unsteady. These flow features correspond well to the measured fluctuating aerodynamic forces.