Fan Flow Control for Improved Efficiency and Noise Reduction

Techsburg, Inc. and the Vibrations and Acoustics Laboratory at Virginia Tech (VAL) are proposing an innovative flow control scheme for fan rotors designed to simultaneously increase fan loading and efficiency while reducing fan radiated noise. The technology uses optimized blowing to prevent flow separation and significantly reduce the downstream wake size. A Phase I STTR proved the feasibility of using suction surface blowing jets to produce a sound power reduction on the order of 7dB and a reduction in losses of 60%. This research will combine an optimized flow control design with alternating blowing concepts. Using alternating blowing with an acoustic liner to attenuate the broadband noise will allow us to maximize the noise reduction and minimize the required mass flow. The amount of work produced by a single compression stage is limited by the amount of diffusion that can occur without large-scale flow separation. Viscous losses within the separated region not only result in an efficiency penalty but also create a large wake behind each of the rotor blades that interact with the downstream exit guide vanes and stators. Left untreated, fan exhaust noise from this interaction is the most dominant perceived noise at takeoff and landing. By using flow control to eliminate separation and the rotor wake, both efficiency gains and noise reduction can be achieved.