Noise control of a blunt trailing-edge flat plate using spanwise discrete blowing

This study experimentally investigates the effect of spanwise discrete blowing on vortex shedding noise of blunt trailing-edge (TE) flat plate, exploring the influences of blowing offset from the TE centre, tilted angle, and flow rate on the noise and flow characteristics. The Reynolds number ( Re_c ) ranges from 4.0 × 10⁵ to 6.6 × 10⁵, corresponding to the wind speeds of U _∞=30 ∼ 50 m/s. Four blowing configurations were tested: central parallel blowing (CPB), offset parallel blowing (OPB), offset tilted blowing ① (OTB①), and offset tilted blowing ② (OTB②). Each configuration was examined under six blowing flow rates, which generate dimensionless blowing intensity A _v of 0.12 ∼ 1.23. Noise measurements demonstrate that the CPB achieves the best noise reduction among the four control schemes. The peak noise can be reduced by more than 15 dB with the CPB when the dimensionless blowing intensity A _v ≥ 0.6, and the OPB & OTB② reduced 10 dB noise as A _v ≥ 0.8, whereas the OTB① achieves nearly no noise reduction. As for the frequency of the noise peak, the Strouhal number increases with A _v under all control schemes. Flow field measurements using Particle Image Velocimetry reveal that the effective noise reduction by the CPB, OPB & OTB② at higher blowing intensity A _v is due to the extension of the separated shear layer and the inhibition of large-scale vortices, especially the CPB, which can almost completely suppress vortex shedding. In contrast, nearly no flow field changes could be observed with the control of the OTB①.