Quasi-steady acoustic response of wall perforations subject to a grazing-bias flow combination

2016

J. Fluid Mech.

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.

Section: Averaged Discharge Coefficientsupporting

confidence: 61%

Section: Literature Reviewmentioning

confidence: 99%

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

2016

J. Fluid Mech.

“…More specific models regarding the interaction of perforated plates with bias flow can be found in Lee et al 32 . Tonon et al 33 investigated the inflow vena contracta, a parameter strongly related to the discharge coefficient, and obtained a semi-empirical correction model for a two-dimensional wall perforation. Scarpato et al 34 , 35 performed extensive work on modeling the acoustic properties of perforated plated backed by a cavity bias flow at low Strouhal number.…”

Section: Ia Literature Reviewmentioning

confidence: 99%

Direct numerical investigation of acoustic liners with single and multiple orifices grazed by a Mach 0.5 boundary layer

46th AIAA Fluid Dynamics Conference

2016

Two groups of direct numerical simulations were conducted to investigate the interaction of a planar incident acoustic field with a cavity-backed circular orifice in the presence of a boundary layer with freestream Mach number of 0.5. The orifice-cavity geometry and grazing flow properties are extracted from a conventional single degree-of-freedom, locallyreacting liner tested at NASA Langley. This paper splits the discussions into two parts: the first part reports the results of single-orifice interaction with a temporal laminar/turbulent grazing boundary layer under the effect of planar acoustic incident sound. The second part moves to a more complicated but realistic liner model by increasing the number of the orifices over a single cavity and aims to investigate flow interactions between different orifices under a spatially-evolving laminar boundary layer. Both groups of the simulations predicts the impedance value with Dean's two-microphone method 1 . The normalized impedance value were scaled by the porosity of the liner and its validity is discussed.

“…More specific models regarding the interaction effect of perforated plates with bias flow can be found in Lee et al [24]. Tonon et al [25] extensively investigated the vena-contraction, a parameter strongly related to the discharge coefficient, and obtained a semi-empirical correction model for a two-dimensional wall perforation.…”

Section: Introductionmentioning

confidence: 99%

Direct numerical simulation and analytical modeling of locally reacting, single degree of freedom acoustic liners with turbulent grazing flow

20th AIAA/CEAS Aeroacoustics Conference

2014

Single degree-of-freedom conventional acoustic liners are widely installed in jet engines to reduce internal engine noise. They work by converting acoustic energy into vorticity-bound fluctuations. Despite being widely used, effective design-stage models of acoustic liners placed in high sound amplitude conditions, possibly with a turbulent grazing flow, are not available due to the near-liner flow complexity and diagnostic challenges. The work presented in this thesis uses direct numerical simulations (DNS) of a compressible, viscous fluid to understand the inherent fluid mechanics and guide reduced-order-model development. In this work, detailed interaction of an incident acoustic field with a Mach 0.5 laminar and turbulent grazing flow with a cavity-backed circular orifice is studied. All results are for tonal excitation at 130 dB from 2.2 -3.0 kHz, or at 3 kHz with 130 -160 dB acoustic amplitude. The results suggest that the liner experiences a drag increase over the baseline geometry with acoustic excitation and that facesheet shear stress measurements, while dominant at low acoustic amplitudes, contribute less at higher acoustic amplitudes. The DNS data further show that the orifice discharge coefficient can be semi-empirically modeled effectively using an acoustic-hydrodynamic scaling. The results indicate that experimental in situ impedance measurements can be contaminated by microphone-orifice interaction. Finally, the time-domain model without grazing flow was extended to include grazing flow by properly modeling the discharge coefficient and the turbulent boundary layer effect. Reasonable agreement of the liner impedance prediction was found with the DNS data. Discrepancies of the prediction suggest the future improvement of the model development.