Validation of a Time- and Frequency-Domain Grazing Flow Acoustic Liner Model

In today's aeroengines, acoustic liners are extensively used to suppress noise. To optimize their placement and tuning, there is a need for acoustic liner models capturing their effect. Traditionally, the presence of a mean flow has been accounted for through the Ingard or later the generalization in form of the Myers boundary condition. This paper shows that a direct use of nominal impedance for the acoustic liner is justified if the mean flow is properly accounted for by the flow equations. An accurate assessment of the acoustic liner in the presence of grazing flows can be obtained without using an acoustic liner model accounting for the How, for example, the Myers boundary condition. Validations have been made for both time and frequency-domain solvers using large-eddy simulations and linearized Navier-Stokes equations.