Implementation of the Ffowcs Williams-Hawkings Equation: Predicting the Far Field Noise From Airfoils While Using Boundary Layer Tripping Mechanisms

2018 ◽  
Author(s):  
Andrew L. Bodling ◽  
Anupam Sharma
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Permeable Surface ◽  
Far Field ◽  
Trailing Edge ◽  
Extraneous Noise ◽  
Field Noise ◽  
High Frequency Waves

A study was done to investigate how boundary layer tripping mechanisms can affect the ability of a permeable surface FW-H solver to predict the far field noise emanating from an airfoil trailing edge. The far field noise in a baseline airfoil as well as the baseline airfoil fitted with fin let fences was analyzed. Two numerical boundary layer tripping mechanisms were implemented. The results illustrated the importance of choosing a permeable integration surface that is outside any high frequency waves emanating from the trip region. The results also illustrated the importance of choosing a boundary layer tripping mechanism that minimizes any extraneous noise so that an integration surface can be taken close to the airfoil.

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.

scholarly journals Bioinspired aerofoil adaptations: the next steps for theoretical models

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190070 ◽  
Author(s):  
Lorna J. Ayton
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Theoretical Modelling ◽  
Experimental Measurements ◽  
Far Field ◽  
Acoustic Analogy ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Theoretical Predictions ◽  
Field Noise

The extended introduction in this paper reviews the theoretical modelling of leading- and trailing-edge noise, various bioinspired aerofoil adaptations to both the leading and trailing edges of blades, and how these adaptations aid in the reduction of aerofoil–turbulence interaction noise. Attention is given to the agreement between current theoretical predictions and experimental measurements, in particular, for turbulent interactions at the trailing edge of an aerofoil. Where there is a poor agreement between theoretical models and experimental data the features neglected from the theoretical models are discussed. Notably, it is known that theoretical predictions for porous trailing-edge adaptations do not agree well with experimental measurements. Previous works propose the reason for this: theoretical models do not account for surface roughness due to the porous material and thus omit a key noise source. The remainder of this paper, therefore, presents an analytical model, based upon the acoustic analogy, to predict the far-field noise due to a rough surface at the trailing edge of an aerofoil. Unlike previous roughness noise models which focus on roughness over an infinite wall, the model presented here includes diffraction by a sharp edge. The new results are seen to be in better agreement with experimental data than previous models which neglect diffraction by an edge. This new model could then be used to improve theoretical predictions for far-field noise generated by turbulent interactions with a (rough) porous trailing edge. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

scholarly journals Wall-Resolved LES Modeling of a Wind Turbine Airfoil at Different Angles of Attack

2020 ◽  
Vol 8 (3) ◽  
pp. 212 ◽  
Author(s):  
Irene Solís-Gallego ◽  
Katia María Argüelles Díaz ◽  
Jesús Manuel Fernández Oro ◽  
Sandra Velarde-Suárez
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Acoustic Waves ◽  
Urban Environments ◽  
Far Field ◽  
Noise Generation ◽  
Noise Propagation ◽  
Trailing Edge ◽  
Wind Turbine Airfoil ◽  
Les Model

Noise has arisen as one of the main restrictions for the deployment of wind turbines in urban environments or in sensitive ecosystems like oceans for offshore and coastal applications. An LES model, adequately planned and resolved, is useful to describe the noise generation mechanisms in wind turbine airfoils. In this work, a wall-resolved LES model of the turbulent flow around a typical wind turbine airfoil is presented and described in detail. The numerical results obtained have been validated with hot wire measurements in a wind tunnel. The description of the boundary layer over the airfoil provides an insight into the main noise generation mechanism, which is known to be the scattering of the vortical disturbances in the boundary layer into acoustic waves at the airfoil trailing edge. In the present case, 2D wave instabilities are observed in both suction and pressure sides, but these perturbations are diffused into a turbulent boundary layer prior to the airfoil trailing edge, so tonal noise components are not expected in the far-field noise propagation. The results obtained can be used as input data for the prediction of noise propagation to the far-field using a hybrid aeroacoustic model.

scholarly journals Effect of Surface Roughness on Boundary Layer Transition and Far Field Noise

2019 ◽  
Author(s):  
Qingqing Ye ◽  
Francesco Avallone ◽  
Daniele Ragni ◽  
Meelan M. Choudhari ◽  
Damiano Casalino
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Boundary Layer Transition ◽  
Far Field ◽  
Layer Transition ◽  
Field Noise ◽  
Effect Of Surface

scholarly journals Control of the Laminar-Turbulent Transition on the Wing Profile by Distributed Suction through a Finely Perforated Surface

2019 ◽  
Vol 14 (4) ◽  
pp. 28-54
Author(s):  
G. R. Grek ◽  
M. M. Katasonov ◽  
V. V. Kozlov ◽  
V. I. Kornilov ◽  
A. V. Kryukov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
High Frequency ◽  
Boundary Layer Separation ◽  
Experimental Investigations ◽  
Mean Flow ◽  
Trailing Edge ◽  
Turbulent Transition ◽  
External Acoustic Field ◽  
The Mean ◽  
Finely Perforated Surface

The results of experimental investigations of the influence of distributed suction through a finely perforated section of a symmetric airfoil on the spatial development of disturbances in the boundary layer are presented. It was found that distributed suction reduces by 10 times the intensity of natural disturbances of the boundary layer and by 20 times the intensity of artificial disturbances generated by an external acoustic field. A spectral analysis of disturbances showed that suction reduces the intensity of high-frequency fluctuations for both natural and forced disturbances. It was found that the distributed suction affects the average flow – when the suction is on, the separation of the boundary layer near the trailing edge of the wing is eliminated. It was found that distributed suction significantly affects the mean flow, up to eliminating the boundary-layer separation near the trailing edge of the wing.

scholarly journals Effect of Surface Roughness Geometry on Boundary-Layer Transition and Far-Field Noise

AIAA Journal ◽  
2021 ◽  
pp. 1-13
Author(s):  
Qingqing Ye ◽  
Francesco Avallone ◽  
Daniele Ragni ◽  
Meelan Choudhari ◽  
Damiano Casalino
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Boundary Layer Transition ◽  
Far Field ◽  
Layer Transition ◽  
Field Noise ◽  
Effect Of Surface

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2012 ◽  
Author(s):  
Clifford Brown
Keyword(s):  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Noise Sources ◽  
Trailing Edge ◽  
Wide Range ◽  
Field Noise ◽  
Interaction Test

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet/Surface Interaction Test was intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. During phase one, the goal was to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet/surface interaction is creating additional noise, and (2) determine regions of interest for more detailed tests in phase two. To meet these phase one objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer (microphone array) and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface was moved through axial positions 2 ≤ xTE/Dj ≤ 20 (measured at the surface trailing edge, xTE, and normalized by the jet diameter, Dj) and radial positions 1 ≤ h/Dj ≤ 20. Far-field and phased array noise data were acquired at each combination of axial and radial surface location using two nozzles and at 8 different jet exit conditions across several flow regimes (subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic cold). The far-field noise results, discussed here, show where the surface shields some of the jet noise and, depending on the location of the surface and the observer, where scrubbing and trailing edge noise sources are created as a surface extends downstream and approaches the jet plume.

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