Active control of fan tones by means of trailing edge blowing

Abstract

At DLR in Berlin, a series of experiments was performed on a laboratory scale fan rig to explore the potential of trailing edge blowing (TEB) for the attenuation of tonal noise of an axial fan stage for the first three blade passage frequencies (BPF). The ventilator consisted of 18 blades, each blade of which was equipped with five internal flow channels, commonly provided with pressurized air through the rotor hub. In configuration 1, all five channels were utilized for noise control. The success of the treatment was monitored over the whole operating range of the fan stage using different mass flow rates of blowing with hardly any positive effect on the noise in the duct. In configuration 2, the outmost two internal channels were blocked by means of aluminium tape (comp. Fig. 1). The latter case provided substantial tonal noise reduction, the result of which is depicted in Fig. 2. […]