Frequency domain simulations for the determination of liner effects on longitudinal wave propagation

Frequency domain simulations are carried out in order to determine the effects of a liner on the propagation of longitudinal waves. On the basis of a CFD/CAA approach, three-dimensional linearized Euler equations (LEE) are transformed into frequency space and discretized using a stabilized Finite-Element technique to provide stable solution procedures and meaningful results. The code is validated on a Grazing Incidence Tube (GIT), which is operated at the NASA Langley Research Center. Results show that the frequency transformed LEE are very suitable to predict the acoustic propagation using experimentally determined liner impedances for different Mach numbers in the tube and further acoustic boundary conditions both at inlet and outlet of the test rig. In comparison to time-domain based approaches, computational times are reduced substantially and numerical instability issues are prevented. Furthermore, the relevance of detailed mean flow profiles and Myers impedance boundary conditions for the accurate prediction of the liner effect on the acoustic wave propagation is addressed.