Parametric study of air curtains for airframe noise reduction

Abstract

The advancement of European society is dependent on safe, efficient, and environmentally-friendly technologies. It is an on-going challenge for European industry to meet customer and legislative requirements, satisfy societal demands and sustain competitiveness in the global arena. Development of novel aircraft concepts requires a complex compromise between contradictory requirements in safety, exhaust emissions, noise, performance and price. Landing gear noise is an example of airframe noise caused by turbulent airflow around aircraft components. Landing gear are very complex and as a result many components such as hydraulic cables, electrical wiring, torque links, front and rear braces etc. are exposed to the airflow. The contribution to the overall level of the generated noise from the various components depends on the specifics of the actual design of the landing gear. Air curtains are a novel concept, currently at a low TRL, which apply an upstream air jet to deflect the flow around a landing gear component, thus reducing the local flow speeds and therefore the aerodynamically generated noise. Small-scale proof-of-concept tests were successfully performed in NLR's Small Anechoic Wind Tunnel using an air curtain to shield a bluff body [1]. Broadband noise reductions of 3–5 dB were obtained using an air curtain with vertical blowing. The noise reductions could be increased by oblique blowing and by applying a small flow deflector directly behind the blowing slot. However, the research found that there is an optimal air curtain flow velocity beyond which the beneficial effects can be lost. This is primarily due to the noise generated by the air curtain itself. [...]