NASA has awarded a $500,000,two-year contract to Virginia-based Techsburg to research the reduction of jet engine fan noise using ejector pump flow control.
The contract, part of NASA's Small Business Technology Transfer (STTR) 2001 Phase II programme, will allow Techsburg to investigate using bleed air, injected from the fan blade trailing edge, to smooth the flow downstream of the fan.
Techsburg vice-president of engineering Stephen Guillot says: "Getting rid of the fan wake and removing non-uniformities in the flow field reduces exhaust guide vane interaction noise."
He adds: "We've looked at using 2% of the total flow, extracted from the low-pressure compressor, but this uses up a large amount of the core flow, so we'll see what can be done with less than 0.3%. Our objective is to minimise the total pressure deficit across the fan."
Brian Fite, aerospace engineer at NASA's Glenn Research Center (GRC), which is managing the project, says this is one idea in an effort to reduce fan noise by 4dB as part of the Quiet Aircraft Technology (QAT) programme. "The fan trailing-edge blowing could give a 1-2dB reduction, but would have to be used with other technologies," says Fite.
He adds that research is limited to fan tip speeds of 130m/s (425ft/s), but it is hoped that this can be expanded to 260m/s. Modern turbofans have tip speeds of more than 300m/s, says Fite.
* In a separate programme, Techsburg has evaluated a similar ejector pump system to improve the aerodynamic efficiency of low-pressure turbines (LPTs) at high-altitude cruise conditions. "At low Reynolds number cruise conditions, laminar flow on the blades leads to flow separation problems," says Guillot. "We initially looked at incorporating a venturi device within the ejector with an orifice to suck sluggish air from the boundary layer, energise it, and re-inject it on the blade's suction surface, but the additional payoff from the suction was not as much as expected. Our current design is a simple ejector pump."
Source: Flight International
