Mathematical simulation of sound propagation in a flow channel with impedance walls

Abstract

The paper considers the specifics of calculating tonal sound propagating in a flow channel with an installed sound absorbing device. The calculation is performed on the basis of numerical integrating on lin earized nonstationary Euler equations using a code developed by the authors based on the so called discon tinuous Galerkin method. Using the linear theory of small perturbations, the effect of the sound absorbing lining of the channel walls is described with the modified value of acoustic impedance proposed by the authors, for which, under flow channel conditions, the traditional classification of the active and reactive types of lining in terms of the real and imaginary impedance values, respectively, remains valid. To stabilize the computation process, a generalized impedance boundary condition is proposed in which, in addition to the impedance value itself, some additional parameters are introduced characterizing certain fictitious prop erties of inertia and elasticity of the impedance surface.

Aircraft Fan Noise Reduction Technology Using Leaned Stator Blades

“…Generally, the modern aircraft engines are designed using combination of the structural noise reduction technologies and passive methods assuming installation of the sound absorbing treatment in engine ducts [1][2]. Among the first group of noise reduction methods are the complying of the cutoff condition, choice of the optimal axial clearance between rotor and stator as on the one hand the increasing of axial clearance leads to noise reduction and on the other hand -to negative increasing of the engine weight.…”