A Study on Local Flow Variations for Landing Gear Noise Research

Abstract

*This paper discusses a systematic study on the local flows in the vicinity of aircraft landing gears with the objective of understanding the flow features, identifying their effects on landing gear noise generation and prediction and developing simple and efficient models to calculate the local flow velocity for gear noise prediction and analysis. To achieve this objective, local flows for various aircraft types and various operation conditions are extracted from a large CFD database and analyzed to reveal the parametric trends of the local flows as a function of parameters such as the aircraft angle of attack and landing gear location. It is shown that for wing mounted gears, the local flows are strongly affected by the high lift system; the circulation around the high lift wing induces a flow under the wing in opposite direction to the free stream flow, and hence, makes the local flow velocity lower than the free stream velocity, by as much as 25 percent at the gear locations. The local velocities are shown to increase monotonically from their minimum values close to the lower surface of the wing to the free stream velocity as the distance from the wing increases. However, for fuselage mounted gears, the trends are opposite; the local flow velocity for nose gears is usually slightly higher than the free stream and it achieves its maximum close to the lower surface of the fuselage with decreasing amplitude with the distance from the fuselage. This is because the nose gears are located in a flow acceleration region downstream of the stagnation point on the nose cone surface, which is approximately defined here as the minimum velocity point. For all gears, it is shown that the local flow velocity is a decreasing function of the aircraft angle of attack. For wing mounted gears, this is due to the increased lift of the wing at large angles of attack, while for nose gears, increasing angles of attack move the stagnation point downstream towards to nose gears, reducing the velocity at the gear location. Based on these flow features, a simple reduced-order model is developed, which correlates the local flow velocity to the free stream velocity, the aircraft angle of attack, the maximum aircraft takeoff weight and the distance from the aircraft. All these parameters are readily available in practical applications, rendering the simple model suitable for landing gear noise prediction. Some qualitative discussions are given on the effects of the local flow features on landing gear noise analysis and prediction.