scholarly journals Influence of the liner-type treatment on the trailing-edge noise generated by a flat plate

2021 ◽  
pp. 1475472X2110238
Author(s):  
Gyuzel Yakhina ◽  
Bastien Dignou ◽  
Yann Pasco ◽  
Stéphane Moreau
Keyword(s):  
Flat Plate ◽  
Reynolds Numbers ◽  
Wire Mesh ◽  
Intermediate Cell ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Flow Recirculation ◽  
Plate Length ◽  
Edge Scattering ◽  
Noise Amplification

Several liner-type treatments (three different rectangular grooves covered by three different low porosity wire-mesh screens) on the trailing edge of a flat plate have been investigated in the anechoic wind-tunnel of Université de Sherbrooke. Far-field acoustic directivity measurements have been achieved at Reynolds numbers based on the plate length from [Formula: see text] to [Formula: see text], yielding radiation maps of all possible liner combinations that are then compared to the reference solid flat plate and to the plate with inserts alone. Noise from the flat plate corresponds to dipolar trailing-edge scattering with an extra shallow hump attributed to the unsteady flow recirculation behind the thick plate. When grooves are added, the latter contribution is amplified and additional cavity noise is observed with several tones and humps. The tones are shown to be resonance between high order modified Rossiter modes and cavity depthwise modes. The hump is a combination of drag dipoles and cavity monopoles from the groove row. The addition of screens always reduces the amplification of the dipolar edge scattering but exhibits very different non-linear responses for the cavity noise. The combination screen with the smallest cells and the insert with the shallowest cavities (corresponding to the same type of treatment applied previously on the Controlled-Diffusion airfoil) yields the lowest levels overall, while the screen with intermediate cell size almost always triggers noise amplification and the screen with a coarse mesh has an intermediate behavior. At high frequencies, the previously reported roughness noise is also observed.

scholarly journals Flow phenomena in the very near wake of a flat plate with a circular trailing edge

2014 ◽  
Vol 756 ◽  
pp. 510-543 ◽  
Author(s):  
Man Mohan Rai
Keyword(s):  
Flat Plate ◽  
Boundary Layers ◽  
Reverse Flow ◽  
Reynolds Numbers ◽  
Shear Layers ◽  
Main Body ◽  
Near Wake ◽  
Trailing Edge ◽  
Plate Length ◽  
First Case

AbstractThe very near wake of a flat plate with a circular trailing edge, exhibiting pronounced shedding of wake vortices, is investigated with data from direct numerical simulations (DNSs). Computations were performed for two cases. In the first case the Reynolds numbers based on plate length and thickness were $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}1.255 \times 10^{6}$ and $1.0 \times 10^{4}$, respectively. In the second case the two Reynolds numbers were $3.025 \times 10^{5}$ and $5.0 \times 10^{3}$, respectively. The separating boundary layers are turbulent and statistically identical thus resulting in a wake that is symmetric in the mean. The focus here is on the instability of the detached shear layers and the evolution of rib-vortex-induced localized regions of reverse flow. These regions detach from the main body of reverse flow in the trailing edge region and are convected downstream. The detached shear layers intermittently exhibit unstable behaviour, sometimes resulting in the development of shear-layer vortices as seen in earlier cylinder flow investigations with laminar separating boundary layers. Only a small fraction of the separated turbulent boundary layer experiences this instability, and also rolls up into the initial shed vortices. The instability causes a broadband peak in pressure spectra computed within the shear layers. Phase-averaged intensity and shear stress distributions of the randomly fluctuating component of velocity in the very near wake are also provided here and compared with those obtained in the near wake. The distributions of the production terms in the transport equations for the turbulent stresses are also provided.

Airfoil Trailing Edge Noise Reduction Using a Boundary-Layer Bump

2019 ◽  
Vol 105 (5) ◽  
pp. 814-826 ◽  
Author(s):  
Yuejun Shi ◽  
Seongkyu Lee
Keyword(s):  
Boundary Layer ◽  
Noise Reduction ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Trailing Edge ◽  
Velocity Deficit ◽  
Trailing Edge Noise ◽  
Field Noise ◽  
High Reynolds

This paper presents a new idea of reducing airfoil trailing edge noise using a small bump in the turbulent boundary layer. First, we develop and validate a new computational approach to predict airfoil trailing edge noise using steady RANS CFD, an empirical wall pressure spectrum model, and Howe's diff raction theory. This numerical approach enables fast and accurate predictions of trailing edge noise, which is used to study the noise reduction from the bump for various airfoil geometries and flow conditions at high Reynolds numbers. Three types of bumps, the suction-side bump, pressure-side bump, and both-side bumps, are studied. The results show that all types of bumps are able to reduce far-field noise up to 10 dB compared to clean airfoils, but their impacts are diff erent in terms of the eff ective frequency range. Also, bumps with four diff erent heights are compared with each other to investigate the eff ect of the height of bumps on noise reduction. It is demonstrated that a bump causes velocity deficit within the boundary layer near the wall. This velocity deficit results in reduced turbulence kinetic energy near the wall, which is responsible for trailing edge noise reduction. Overall, this paper demonstrates the potential of a boundary-layer bump in trailing edge noise reduction and sheds light on the physical mechanism of noise reduction with boundary-layer bumps.

Wall Effect on Separated Flow Around an Inclined Flat Plate at High Incidence

2013 ◽  
Author(s):  
Chuanjin Lan ◽  
Laibing Jia ◽  
Zhen Li ◽  
Yanbao Ma
Keyword(s):  
Flat Plate ◽  
Practical Importance ◽  
Angle Of Attack ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Bluff Bodies ◽  
Trailing Edge ◽  
Plate Length ◽  
Gap Ratio ◽  
Lift And Drag

The flow around bluff bodies has received a great deal of attention due to its practical importance in engineering and scientific relevance in fluid mechanics. The largely separated turbulent flow can be triggered by an inclined flat plate with sharp leading and trailing edge and the presence of wall can alternate the flow structures greatly. This paper applied the Unsteady Reynolds-averaged Navier-Stokes (URANS) model to simulate the vortex shedding phenomenon over the inclined flat plate for a Reynolds number Re = 20 000 with different angle of attack α and gap ratio D/L, the ratio of the distance from the plate to the wall (D) to the plate length (L). Vortex generation from the leading and trailing edge was captured clearly and the transportation and development of vortex structures were shown for different parameters. The smaller the gap ratio is, the more the flow characteristics are affected by the wall presence. The integral quantities, such as lift and drag coefficients show different peak values for different angle of attack.

scholarly journals On secondary tones arising in trailing-edge noise at moderate Reynolds numbers

2020 ◽  
Vol 79 ◽  
pp. 54-66
Author(s):  
Túlio R. Ricciardi ◽  
Walter Arias-Ramirez ◽  
William R. Wolf
Keyword(s):  
Reynolds Numbers ◽  
Trailing Edge ◽  
Trailing Edge Noise

Detached shear-layer instability and entrainment in the wake of a flat plate with turbulent separating boundary layers

2015 ◽  
Vol 774 ◽  
pp. 5-36 ◽  
Author(s):  
Man Mohan Rai
Keyword(s):  
Shear Layer ◽  
Flat Plate ◽  
Boundary Layers ◽  
Power Law ◽  
Reynolds Numbers ◽  
Vortex Generation ◽  
Shear Layer Instability ◽  
Trailing Edge ◽  
Velocity Statistics ◽  
Entrainment Process

The near and very near wake of a flat plate with a circular trailing edge, with vigorous vortex shedding, is investigated with data from direct numerical simulations (DNS). Computations were performed for four different combinations of the Reynolds numbers based on plate thickness ($D$) and momentum thickness near the trailing edge (${\it\theta}$). Unlike the case of the cylinder, these Reynolds numbers are independent parameters for the flat plate. The objectives of the study are twofold, to investigate the entrainment process when the separating boundary layers are turbulent and to better understand the instability of the detached shear layers (DSLs). A visualization of the entrainment process, the effect of changing the ratio ${\it\theta}/D$ on entrainment and wake-velocity statistics, and a way of understanding entrainment in a phase-averaged sense via distributions of the turbulent transport rate are provided here. The discussion on shear-layer instability focuses on the role of log-layer eddies in the destabilization process, the effect of high-speed streaks in the turbulent boundary layer in the vicinity of the trailing edge on shear-layer vortex generation rates, and a relationship between the prevalence of shear-layer vortex generation and shedding phase that is a result of an interaction between the shedding process and the shear-layer instability mechanism. A power-law relationship between the ratio of shear-layer and shedding frequencies and the Reynolds numbers mentioned above is obtained. A discussion of the relative magnitudes of the exponents is provided. A second power-law relationship between shed-vortex strength and these two Reynolds numbers is also proposed.

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