Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

Abstract

Direct numerical simulations are used to study the interaction of a cavity-backed circular orifice with grazing laminar and turbulent boundary layers and incident sound waves. The flow conditions and geometry are representative of single degree-of-freedom acoustic liners applied in the inlet and exhaust ducts of aircraft engines and are the same as those from experiments conducted at NASA Langley. The simulations identify the fluid mechanics of how the sound field and state of the grazing boundary layer impact the in-orifice flow and suggest a simple flow analogy that enables scaling estimates. From the scaling estimates the simulations are then used to develop reduced-order models for the in-orifice flow and a time-domain impedance model is constructed. The liner is found to increase drag at all conditions studied by an amount that increases with the incident sound pressure amplitude.

Experimental Assessment of the Effect of Temperature Gradient Across an Aeroacoustic Liner

“…This is explained by the generation, during a half-period of the excitation cycle, of a vortex above the upper orifice of the hole, whereas during the other half-period a similar mechanism takes place inside the cavity. These phenomena are explained numerically for instance in the work of Zhang & Bodony [33] and experimentally exhibited in Ingard & Labate [34] or Hersh & Walker [35]. We can infer that this modification of the near-wall region w increases the h convection heat transfer coefficient.…”

Liner Impedance Eduction Under Shear Grazing Flow at a High Sound Pressure Level

“…8 This leads to a modification of the impedance (mainly an increase of the resistance). [9][10][11] These studies show that the impedance depends on the incident sound pressure level in the presence of high SPL. In a lined duct configuration, the sound pressure level may be much higher upstream of the liner than downstream of the liner.…”

Design of broadband time-domain impedance boundary conditions using the oscillatory-diffusive representation of acoustical models

“…However, a departure from LTI modeling is invariably caused by: an inviscid basic flow, modeled with the Ingard-Myers boundary condition; 26 nonlinear phenomena, such as vortex shedding, that arise from high sound pressure levels. 27 An example of nonlinear impedance model is that of Melling,5 in which the impedance exhibits a dependency on the acoustic velocity itself:ẑ s (s, u n ).…”