Mechanism for Increased Viscous Drag over Porous Sheet Acoustic Liners

Jasinski, Christopher; Corke, Thomas

doi:10.2514/1.j059039

Cited by 13 publications

(5 citation statements)

References 36 publications

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“…This can be used to confront the burst profiles above the smooth to those above the perforated wall; this should give an indication of how the turbulent activity is modified in the presence of the cavities. As expected, the shape of a burst profile for the smooth condition is dominated by the presence of a bump with a peak in the region 10 < Y þ < 20, as reported by Blackwelder and Kaplan (1976) or Jasinski and Corke (2020). A comparison between the smooth and perforated walls in the middle of the model is reported in Fig.…”

Section: Number Of Burstssupporting

confidence: 72%

Modification of a turbulent boundary layer by circular cavities

et al. 2022

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It is shown how well-chosen perforations in a wall flow can locally reduce skin friction drag by modifying the generation of bursts in the boundary layer. For this purpose, a detailed hot wire experimental boundary layer investigation of the flow past a perforated plate, complemented with large eddy simulations, is carried out and compared to the smooth baseline. The perforated plate is obtained with an array of flush-mounted circular cavities. These cavities are disposed in a periodic staggered arrangement. For the three tested flow velocities, the momentum thickness based Reynolds number varies from 1830 to 3380 and the cavity diameter and spacing in wall units respectively from 130 to 250 and 587 to 1075, the latter being identical in both spanwise and streamwise directions. The mean velocity profiles evidence a thickening of the viscous sublayer and a decrease of the friction velocity as compared to the smooth wall case. The application of the Variable Interval Time Averaging (VITA) technique highlights an upward shift of the bursts from the wall and an attenuation of the average burst intensity and duration.Spanwise measurements evidence an overall bursts attenuation despite the lack of spanwise uniformity.The 3D mean flow topology arising from the large eddy simulations provides evidences of the qualitative similarities between the current setup and the spanwise wall oscillations.

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Section: Number Of Burstssupporting

confidence: 72%

Modification of a turbulent boundary layer by circular cavities

et al. 2022

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“…The average voltage was converted to force using a predetermined linear voltage–force calibration. Direct drag measurements by Jasinski & Corke (2020) using the same force balance with a smooth platen surface over a range of momentum thickness Reynolds numbers matched the Coles–Fernholz relation (Baars et al. 2016) to within 1 %.…”

Section: Experimental Set-upmentioning

confidence: 67%

Characteristics of drag-reduced turbulent boundary layers with pulsed-direct-current plasma actuation

2021

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“…Although the sound attenuation mechanism is well understood, the aerodynamic characteristics of these surfaces are less clear. Several authors agree that liners increase aerodynamic drag as compared with a hydraulically smooth wall (Wilkinson 1983;Howerton & Jones 2015;Jasinski & Corke 2020). However, an extensive literature study summarized in table 1 shows that reported values for the actual drag increase caused by acoustic liners vary between 2 % and 500 %.…”

Section: Introductionmentioning

confidence: 99%

Turbulence and added drag over acoustic liners

2023

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We present pore-resolved compressible direct numerical simulations of turbulent flows grazing over perforated plates, that closely resemble the acoustic liners found on aircraft engines. Our direct numerical simulations explore a large parameter space including the effects of porosity, thickness and viscous-scaled diameter of the perforated plates, at friction Reynolds numbers $\textit {Re}_\tau = 500\unicode{x2013}2000$ , which allows us to develop a robust theory for estimating the added drag induced by acoustic liners. We find that acoustic liners can be regarded as porous surfaces with a wall-normal permeability and that the relevant length scale characterizing their added drag is the inverse of the wall-normal Forchheimer coefficient. Unlike other types of porous surfaces featuring Darcian velocities inside the pores, the flow inside the orifices of acoustic liners is fully turbulent, with a magnitude of the wall-normal velocity fluctuations comparable to the peak in the near-wall cycle. We provide clear evidence of a fully rough regime for acoustic liners, also confirmed by the increasing relevance of pressure drag. Once the fully rough asymptote is reached, canonical acoustic liners provide an added drag comparable to that of sand-grain roughness with viscous-scaled height matching the inverse of the viscous-scaled Forchheimer permeability of the plate.

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Mechanism for Increased Viscous Drag over Porous Sheet Acoustic Liners

Cited by 13 publications

References 36 publications

Modification of a turbulent boundary layer by circular cavities

Modification of a turbulent boundary layer by circular cavities

Characteristics of drag-reduced turbulent boundary layers with pulsed-direct-current plasma actuation

Turbulence and added drag over acoustic liners

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