scholarly journals Effects of porous trailing edge on aerodynamic noise characteristics

2020 ◽  
Vol 19 (3-5) ◽  
pp. 254-271 ◽  
Author(s):  
Minghui Zhang ◽  
Tze Pei Chong
Keyword(s):  
High Reynolds Number ◽  
Experimental Testing ◽  
Low Frequency ◽  
Reynolds Numbers ◽  
Broadband Noise ◽  
Aerodynamic Noise ◽  
Trailing Edge ◽  
Noise Characteristics ◽  
Trailing Edges ◽  
High Reynolds

The objective of this work is to investigate the effect of the porous trailing edge on the aeroacoustics performance of the NACA 65(12)-10 aerofoil. The motivation behind this study is to investigate the effect of the porous parameters to explore the noise control concepts. Experimental testing in an aeroacoustics open jet wind tunnel was performed at chord-based Reynolds numbers between 0.2 and 0.6 million, and effective angles of attack at ±1.7 degree, including at 0 degrees. The porous trailing edge at porosity 30% with different holes diameters and the length of these porous trailing edges are used in the acoustic experiments. The study reveals that the level of the reduction of the broadband noise becomes larger as the diameter of the holes decreases and the length of the porous trailing edge increases at lower Reynolds numbers. Bluntness-induced tone noise is produced at high Reynolds number. Meanwhile, the porous trailing edge can suppress the laminar instability noise at the middle and low frequency regions.

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Aerodynamic noise characteristics of airfoils with morphed trailing edges

2022 ◽  
Vol 93 ◽  
pp. 108892
Author(s):  
Hasan Kamliya Jawahar ◽  
SH. S. Vemuri ◽  
Mahdi Azarpeyvand
Keyword(s):  
Aerodynamic Noise ◽  
Noise Characteristics ◽  
Trailing Edges

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.

Correlated Compressible and Incompressible Channel Flows

1997 ◽  
Vol 119 (4) ◽  
pp. 911-915 ◽  
Author(s):  
C. Crnojevic´ ◽  
V. D. Djordjevic´
Keyword(s):  
Cross Section ◽  
High Reynolds Number ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Isothermal Flow ◽  
Governing Equations ◽  
Adiabatic Flow ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Reynolds Number Flows

Compressible flow in channels of slowly varying cross section at moderately high Reynolds numbers is treated in the paper by employing some Stewartson-type transformations that convert the problem into an incompressible one. Both adiabatic flow and isothermal flow are considered, and a Poiseuille-type incompressible solution is mapped onto compressible plane in order to generate some exact solutions of the compressible governing equations. The results show striking effects that viscosity may have upon the flow characteristics in this case, in comparison with more conventional high Reynolds number flows.

Stability of non-parabolic flow in a flexible tube

1999 ◽  
Vol 395 ◽  
pp. 211-236 ◽  
Author(s):  
V. SHANKAR ◽  
V. KUMARAN
Keyword(s):  
Reynolds Number ◽  
Velocity Profile ◽  
Asymptotic Analysis ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Flexible Tube ◽  
Developing Flow ◽  
Parabolic Flow ◽  
High Reynolds ◽  
The Stability

Flows with velocity profiles very different from the parabolic velocity profile can occur in the entrance region of a tube as well as in tubes with converging/diverging cross-sections. In this paper, asymptotic and numerical studies are undertaken to analyse the temporal stability of such ‘non-parabolic’ flows in a flexible tube in the limit of high Reynolds numbers. Two specific cases are considered: (i) developing flow in a flexible tube; (ii) flow in a slightly converging flexible tube. Though the mean velocity profile contains both axial and radial components, the flow is assumed to be locally parallel in the stability analysis. The fluid is Newtonian and incompressible, while the flexible wall is modelled as a viscoelastic solid. A high Reynolds number asymptotic analysis shows that the non-parabolic velocity profiles can become unstable in the inviscid limit. This inviscid instability is qualitatively different from that observed in previous studies on the stability of parabolic flow in a flexible tube, and from the instability of developing flow in a rigid tube. The results of the asymptotic analysis are extended numerically to the moderate Reynolds number regime. The numerical results reveal that the developing flow could be unstable at much lower Reynolds numbers than the parabolic flow, and hence this instability can be important in destabilizing the fluid flow through flexible tubes at moderate and high Reynolds number. For flow in a slightly converging tube, even small deviations from the parabolic profile are found to be sufficient for the present instability mechanism to be operative. The dominant non-parallel effects are incorporated using an asymptotic analysis, and this indicates that non-parallel effects do not significantly affect the neutral stability curves. The viscosity of the wall medium is found to have a stabilizing effect on this instability.

High Reynolds Number Airfoil Simulations Using the Immersed Boundary Method

2012 ◽  
Author(s):  
James P. Johnson ◽  
Gianluca Iaccarino ◽  
Kuo-Huey Chen ◽  
Bahram Khalighi
Keyword(s):  
Immersed Boundary Method ◽  
High Reynolds Number ◽  
Aerodynamic Force ◽  
Reynolds Numbers ◽  
Computational Approach ◽  
Immersed Boundary ◽  
Pressure Distributions ◽  
Boundary Method ◽  
High Reynolds ◽  
Naca 0012

The Immersed-Boundary Method is coupled to an incompressible-flow RANS solver, based on a two-equation turbulence model, to perform unsteady numerical simulations of airflow past the NACA-0012 airfoil for several angles of attack and Reynolds numbers of 5.0×105 and 1.8×106. Qualitative characterizations of the flow in the vicinity of the airfoil are obtained to show the need for locally refined grids to capture the thin boundary layers close to the airfoil leading edges. Quantitative analysis of aerodynamic force coefficients and wall pressure distributions are also reported and compared to experimental results and those from body-fitted grid simulations using the same solver to assess the accuracy and limitations of this approach. The Immersed-Boundary simulations compared well to the experimental and body-fitted results up to the occurrence of separation. After that point, neither computational approach provided satisfactory solutions.

Spectral energy transfer in high Reynolds number turbulence

1977 ◽  
Vol 79 (2) ◽  
pp. 337-359 ◽  
Author(s):  
K. N. Helland ◽  
C. W. Van Atta ◽  
G. R. Stegen
Keyword(s):  
Reynolds Number ◽  
Energy Transfer ◽  
Energy Spectrum ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Second Order ◽  
Spectral Energy ◽  
Local Isotropy ◽  
High Reynolds ◽  
Good Agreement

The spectral energy transfer of turbulent velocity fields has been examined over a wide range of Reynolds numbers by experimental and empirical methods. Measurements in a high Reynolds number grid flow were used to calculate the energy transfer by the direct Fourier-transform method of Yeh & Van Atta. Measurements in a free jet were used to calculate energy transfer for a still higher Reynolds number. An empirical energy spectrum was used in conjunction with a local self-preservation approximation to estimate the energy transfer at Reynolds numbers beyond presently achievable experimental conditions.Second-order spectra of the grid measurements are in excellent agreement with local isotropy down to low wavenumbers. For the first time, one-dimensional third-order spectra were used to test for local isotropy, and modest agreement with the theoretical conditions was observed over the range of wavenumbers which appear isotropic according to second-order criteria. Three-dimensional forms of the measured spectra were calculated, and the directly measured energy transfer was compared with the indirectly measured transfer using a local self-preservation model for energy decay. The good agreement between the direct and indirect measurements of energy transfer provides additional support for both the assumption of local isotropy and the assumption of self-preservation in high Reynolds number grid turbulence.An empirical spectrum was constructed from analytical spectral forms of von Kármán and Pao and used to extrapolate energy transfer measurements at lower Reynolds number to Rλ = 105 with the assumption of local self preservation. The transfer spectrum at this Reynolds number has no wavenumber region of zero net spectral transfer despite three decades of $k^{-\frac{5}{3}}$. behaviour in the empirical energy spectrum. A criterion for the inertial subrange suggested by Lumley applied to the empirical transfer spectrum is in good agreement with the $k^{-\frac{5}{3}}$ range of the empirical energy spectrum.

Unsteady effects of strong shock-wave/boundary-layer interaction at high Reynolds number

2017 ◽  
Vol 823 ◽  
pp. 617-657 ◽  
Author(s):  
Vito Pasquariello ◽  
Stefan Hickel ◽  
Nikolaus A. Adams
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
High Reynolds Number ◽  
Separation Bubble ◽  
Low Frequency ◽  
Boundary Layer Interaction ◽  
High Reynolds ◽  
Unsteady Effects

We analyse the low-frequency dynamics of a high Reynolds number impinging shock-wave/turbulent boundary-layer interaction (SWBLI) with strong mean-flow separation. The flow configuration for our grid-converged large-eddy simulations (LES) reproduces recent experiments for the interaction of a Mach 3 turbulent boundary layer with an impinging shock that nominally deflects the incoming flow by $19.6^{\circ }$. The Reynolds number based on the incoming boundary-layer thickness of $Re_{\unicode[STIX]{x1D6FF}_{0}}\approx 203\times 10^{3}$ is considerably higher than in previous LES studies. The very long integration time of $3805\unicode[STIX]{x1D6FF}_{0}/U_{0}$ allows for an accurate analysis of low-frequency unsteady effects. Experimental wall-pressure measurements are in good agreement with the LES data. Both datasets exhibit the distinct plateau within the separated-flow region of a strong SWBLI. The filtered three-dimensional flow field shows clear evidence of counter-rotating streamwise vortices originating in the proximity of the bubble apex. Contrary to previous numerical results on compression ramp configurations, these Görtler-like vortices are not fixed at a specific spanwise position, but rather undergo a slow motion coupled to the separation-bubble dynamics. Consistent with experimental data, power spectral densities (PSD) of wall-pressure probes exhibit a broadband and very energetic low-frequency component associated with the separation-shock unsteadiness. Sparsity-promoting dynamic mode decompositions (SPDMD) for both spanwise-averaged data and wall-plane snapshots yield a classical and well-known low-frequency breathing mode of the separation bubble, as well as a medium-frequency shedding mode responsible for reflected and reattachment shock corrugation. SPDMD of the two-dimensional skin-friction coefficient further identifies streamwise streaks at low frequencies that cause large-scale flapping of the reattachment line. The PSD and SPDMD results of our impinging SWBLI support the theory that an intrinsic mechanism of the interaction zone is responsible for the low-frequency unsteadiness, in which Görtler-like vortices might be seen as a continuous (coherent) forcing for strong SWBLI.

An Intermittent High-Reynolds-Number Wind Tunnel

1977 ◽  
Vol 28 (4) ◽  
pp. 259-264 ◽  
Author(s):  
J L Stollery ◽  
A V Murthy
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Simple Method ◽  
High Reynolds Numbers ◽  
Reservoir Conditions ◽  
High Reynolds ◽  
Cryogenic Wind Tunnel ◽  
Performance Estimates

SummaryThe paper suggests a simple method of generating intermittent reservoir conditions for an intermittent, cryogenic wind tunnel. Approximate performance estimates are given and it is recommended that further studies be made because this type of tunnel could be valuable in increasing the opportunities for research at high Reynolds numbers.

scholarly journals Lattice Boltzmann Method Simulations of High Reynolds Number Flows Past Porous Obstacles

2019 ◽  
Vol 11 (03) ◽  
pp. 1950028 ◽  
Author(s):  
N. M. Sangtani Lakhwani ◽  
F. C. G. A. Nicolleau ◽  
W. Brevis
Keyword(s):  
Reynolds Number ◽  
Lattice Boltzmann Method ◽  
Turbulent Flows ◽  
Lattice Boltzmann ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Navier Stokes Equation ◽  
High Reynolds ◽  
Boltzmann Method ◽  
Reynolds Number Flows

Lattice Boltzmann Method (LBM) simulations for turbulent flows over fractal and non-fractal obstacles are presented. The wake hydrodynamics are compared and discussed in terms of flow relaxation, Strouhal numbers and wake length for different Reynolds numbers. Three obstacle topologies are studied, Solid (SS), Porous Regular (PR) and Porous Fractal (FR). In particular, we observe that the oscillation present in the case of the solid square can be annihilated or only pushed downstream depending on the topology of the porous obstacle. The LBM is implemented over a range of four Reynolds numbers from 12,352 to 49,410. The suitability of LBM for these high Reynolds number cases is studied. Its results are compared to available experimental data and published literature. Compelling agreements between all three tested obstacles show a significant validation of LBM as a tool to investigate high Reynolds number flows in complex geometries. This is particularly important as the LBM method is much less time consuming than a classical Navier–Stokes equation-based computing method and high Reynolds numbers need to be achieved with enough details (i.e., resolution) to predict for example canopy flows.

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