Effect of Bubble Seal on Slat Noise

This paper reports a study of the sound emitted by a slat of a two-dimensional three-element MD30P30N airfoil, on which a two-dimensional excrescence was installed to represent a sealing device. Experiments were conducted in a closed-test-section wind-tunnel, and a conventional beamforming technique combined with DAMAS deconvolution method was employed for the evaluation of the radiated noise. Nine seal positions along the slat cove wall and six different seal cross sections were tested for 3-9 deg angles of attack and 34 m/s freestream speed. Mean static pressure measurements on the airfoil surface indicated that the seals did not impact the airfoil lift but significantly affected the slat noise signature, particularly the low-frequency narrowband peaks. At some positions, the narrowband peaks were increased up to 18 dB/Hz, whereas for other positions, they were virtually suppressed. At the noisiest position, even a seal whose height was 1.33% of the slat chord strongly affected the slat noise signature. Lattice Boltzmann numerical simulations in combination with the Ffowc Williams-Hawkings analogy were conducted for experimental cases selected and revealed the strong effect of the seal on the mean flow and the turbulence recirculation in the slat cove.