| Abstrakt: |
In this paper, a model of sound generation by blade--vortex interaction (BVI) is offered for helicopter rotor operating at subsonic regime (M = 0,2). We find the quantitative limits of its use. Based on three-dimensional non-stationary equation of small perturbations spreading, the problem of sound generation by parabolic blade and Taylor's vortex, situated at a certain distance from the blade, is solved. To solve this problem, we use the numerical-analytical method. The method allows calculating the near-field sound potential and its derivatives. The pressure coefficient analysis shows that the disposition of the blade-vortex interaction generates three surges like shock waves of A, B, C types (by Tijeman). However, interaction amplitudes are smaller than the ones for transonic regime. In addition, we reveal that BVI noise level is 10Db (with respect to 2 ⋅ 10-5Pa) more than the noise level in the similar problem without a vortex in the flux. The numerical calculation shows that the limit distance, where the model is acceptable, is more than 1, 5Rc (Rc is core radius). When the distance between vortex core and rotor blade increases, the BVI-noise level decreases. [ABSTRACT FROM AUTHOR] |
