Aerodynamic and Acoustic Measurements of a Single Landing Gear Wheel

This paper presents the results of an experimental study conducted on a 33% scale isolated landing gear wheel, with ‘simple’ and ‘complex’ hub configurations, the aim of which was to gather a comprehensive set of aerodynamic and acoustic data for validating CFD and CAA computations. Aerodynamic measurements were conducted in the Southampton 2.1 m × 1.5 m low speed wind tunnel, using oil flow, pressure tapping, pressure transducers, particle image velocimetry and force balance. A number of interesting features were noted, such as the presence of vortices rolling up behind the wheel to form part of the wake and broadband spectral peaks in some of the surface pressure data, especially within the hub cavity. Overall however, the hub design had little effect on the aerodynamic data. Acoustic tests were performed in the QinetiQ Noise Test Facility (NTF), where a traversing microphone array was used to measure the directivity and levels of the wheel noise in the farfield. The directivity characteristics have been used to positively identify some sources, with the support strut dominant at low frequencies and hub noise dominant in the mid frequencies, but other sources also contribute. At a freestream speed of 78 m/s, the hub noise was characterized by broadband peaks at 630 Hz and 1250 Hz, which did not scale with Strouhal number. Hence, these are linked to the cavity dimensions, and the relative levels of the peaks depended on the hub configuration. Radiation of the hub noise is predominantly along the direction of the wheel axle, and so noise radiation towards the ground is dominated by the other sources arising from the flow separations and vortices seen in the aerodynamic data. The studies provide a physical insight into the flow around an isolated landing gear wheel and can serve as a benchmark case.