Non-Intrusive Measurements of a Blunt Circular Cylinder in a Magnetic Suspension Wind Tunnel

Aerodynamic force and base pressure on axial cylinders as well as flow fields around them were measured at 100,000 of Reynolds number based on their diameter with the JAXA 60cm magnetic suspension and balance system (MSBS), a digital telemeter system, and a particle image velocimetry (PIV). The models were suspended by the MSBS without any support interference. The fineness ratio of them ranged from 1.27 to 1.79. The flow fields were measured in the cross section of the wake perpendicular to the model axis and were also measured in the parallel section including model axis. The test results showed that these three devices could be used concurrently. At the JAXA 60cm MSBS, estimated unsteady aerodynamic force less than about 15Hz could be evaluated successfully. A peak in the power spectrum of the drag fluctuations was observed at about 1.5 Hz (Strouhal number of approximately 0.012) which corresponded to a peak in the power spectrum of the base pressure fluctuations, but absent in the side force spectrum. This is considered to be caused by the axial oscillation of the recirculation region. The Strouhal number of the main base pressure fluctuating frequency was 0.34 which corresponded to large scale vortex shedding. Numerous longitudinal vortices were observed in the unsteady cross sectional flow field of the wake perpendicular to the cylinder axis and they moved widely in the field. Any sting mount of an axial cylinder would have interfered with the flow field to make such observations.