Computational Analysis of the Stand-off Distance Effects on Edgetone by LBM

다국어 초록 (Multilingual Abstract)

An edgetone is the discrete tonal or narrow-band sound generated by an oscillating free layer, impinging on a rigid surface. In this study, the geometric effects of stand-off distance between the nozzle outlet and the wedge for w/d = 3, 6, 9 and 9 are investigated to verify the feedback-loop of edgetone using lattice Boltzmann model with 21 bits, which is introduced a flexible specific heat ratio γ to simulate diatomic gases. The edges consist of wedge with angle 20 degree (for symmetric type) and 23 degree (for inclined type). The computational results show three clear points. I) When the distance from the wedge to the nozzle exit is less than w/d=3.0, there is inadequate room for the jet to blend and the flow splits more or less evenly on each side of the edge, and the edgetone, therefore, does not occur. 2) For the case of w/d=6.0, the jet oscillates in periodic fashion, 3) while the cases over w/d=9.0, the jet also oscillate but the flow patterns do not show periodicity. According to Brown's experiment, when the distance from the wedge to nozzle exit is greater than w/d =20.0, the acoustic feedback, with strength decreasing linearly with distance, would be too week to trigger alternate vortex shedding at the nozzle exit, and the results obtained was qualitatively agreement with previous works.