VORTICITY AMPLIFICATION AND ITS EFFECT ON FLOW SEPARATION FROM LANDING GEAR WHEELS

Noise generated by landing gears has become one of the principle issues of aviation in recent years due to the increasing requirements in noise standards. This noise results mainly from the interactions of the fluctuating flow... [ view full abstract ]

Noise generated by landing gears has become one of the principle issues of aviation in recent years due to the increasing requirements in noise standards. This noise results mainly from the interactions of the fluctuating flow past landing gears with the surface components of the aircraft. For this reason, understanding of the unsteady flow topology for these systems can play an important role in the development of the next-generation, quieter landing-gear designs.
The flow near the stagnation point of landing gear wheels has been previously shown to support a mechanism for inbound streams of weak vorticity to collect, grow, and amplify into large-scale discrete vortex structures. Inbound vorticity may be present due to upstream aircraft components, propeller downwash, or atmospheric turbulence. The current experimental study is an extension of the previous work to investigate the effects of these vortex structures on the separation characteristics of the flow around the outboard sides of the wheels.
Experiments were conducted in a recirculating-type water tunnel on a two-wheel landing gear model. This model was a simplified, 30%-scaled-down model of an actual front landing gear used in Bombardier aircraft. The complete test model consists of two wheels, an axle, a main strut and a support strut. Qualitative understanding of the flow topology was achieved by employing the hydrogen bubble visualization technique and quantitative measurements were performed using Particle Image Velocimetry (PIV). The upstream vorticity source is a platinum wire (with a diameter d of 100 μm) placed 30 mm upstream of the model wheels. The Reynolds number based on the diameter of this wire is 21 and based on the diameter of the landing-gear wheel (D = 152 mm) is 32,500. During the tests, inbound pair of vorticity streams impinged at the wheel surface where maximum vortex growth and amplification occurs, as identified by previous experiments, and the effect of this amplification on the separation characteristics of the flow from the wheels is investigated. The growth and shedding of the resulting vortical structures is shown to alter the shape and size of the separation bubbles on the outboard sides of the wheels. A vortex identification and tracking method is applied to map the growth and movement of the observed structures.
The results indicate that the vortex structures produced from vorticity amplification act to reduce the size of the mean separation bubbles on the outboard sides of the wheels.