By K Attenborough; V I Tokarev; Oleksandr Zaporozhets
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Extra info for Aircraft noise propagation, exposure & reduction : assessment , prediciton and control
The approaches to noise normalization can be categorized as sanitary or technical. Sanitary noise normalization establishes the limitations on noise under conditions of insigniﬁcant harmful inﬂuence on man. Technical noise normalization establishes the maximum noise levels with regard to technically achievable methods of noise reduction for given acoustic sources. The sanitary norms determine the necessary noise attenuation and the technical norms specify the attainable noise levels of the equipment.
To calculate the parameters of turbulent ﬂow, we introduce non-dimensional inner variables xi = tVj xi vi a , vi = , τ = ,a = , L Vj L a0 where L, Vj deﬁne jet turbulence length and velocity scales, respectively. 33) 24 A review of the aircraft noise problem where h = ρ/ρ0 . The asymptotic expansion of the inner solution is h(x, τ , M) = 1 + δ1 (M)σ1 (x, τ ) + δ2 (M)σ2 (x, τ ) + . . , a2 = 1 + δ1 (M)a21 (x, τ ) + . . , (0) (1) vi = vi (x, τ ) + δ1 (M)vi . . , where for M →0, the variables x, τ are ﬁxed.
Propeller noise arises as a result of the periodic displacement of the air by the volume of a passing blade (thickness noise). The pressure ﬂuctuation due to lift and draft disturbance gives the loading noise of the propeller. The propeller noise spectrum contains broadband and harmonic noise. The harmonic noise has frequencies given by fk = nzk, where k = 1, 2, . , n is rotational speed and z is the number of blades. If the propeller has a small number of blades, then for subsonic blade section speeds, the noise is determined in the main by the ﬁrst two harmonics.
Aircraft noise propagation, exposure & reduction : assessment , prediciton and control by K Attenborough; V I Tokarev; Oleksandr Zaporozhets