Trailing Edge Blowing of Fan Blades

Abstract

*† ‡ The wakes of model fan blades containing internal flow passages and trailing edge slots were carefully documented to investigate the potential for reductions in tone and broadband noise produced by aircraft engines. Measurements were taken at four locations downstream of the blade row of the Virginia Tech Low Speed Linear Cascade Wind Tunnel at a variety of blowing rates ranging from 0 to 2.7% of the blade passage mass flow. Low blowing rates were actually found to increase the wake deficit compared to the no blowing case, whereas higher blowing rates greatly reduced it and attenuated turbulence levels. Changes in wake structure produced by blowing are actually completed over a fairly short region close to the trailing edge. Blowing produces significant reduction of the pitchwise spatial correlation of all the components of velocity in the wakes and, at the higher blowing rates, tends to isotropize the turbulence. Integral lengthscales decrease with increased blowing rate. Proper orthogonal decomposition revealed that the blown wakes have a more organized, although less intense, turbulence structure. Implications of these results for noise reduction are discussed.