Statistical Turbulence Modelling of Airfoil Trailing Edge Noise (original) (raw)
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Statistical estimation of turbulent trailing edge noise
2010
ABSTRACT A new computational aeroacoustic model suitable for the prediction of turbulent airfoil trailing edge noise is presented. The method (known as the RANS based Statistical Noise Model or RSNM) combines numerically generated, mean turbulence information with a Green's function for a semi-infinite half-plane to generate a far-field acoustic auto-spectrum.
2012
Abstract Noise generated by turbulent flow past a sharp edge is important in the design of a variety of applications such as aircraft and wind turbines. It is therefore useful to have predictive methods that can capture the effects of subtle design changes on the flow and resulting radiated noise. In this paper, such a methodology is presented and used to predict noise from a sharp-edged strut with a turbulent boundary layer.
Investigation of Airfoil Trailing Edge Noise with Advanced Experimental and Numerical Methods
2014
The investigation of the noise emitted from the trailing edge (TE) of a Somers S834 airfoil section with advanced experimental and numerical methods is presented. The airfoil section is placed in a low noise, low turbulence small aeroacoustic wind tunnel. To mimic a relatively large target Reynolds number the boundary layer on the airfoil has to be tripped. An unsteady large-eddy simulation (LES) provides the input data for airfoil self noise prediction models. Standard microphone correlation as well as microphone array based techniques were applied to distinguish trailing edge noise (TEN) from ambient sound and for quantification. The carefully applied boundary layer tripping produced the targeted boundary layer parameters in the TE region of the airfoil. The TE of the airfoil was found to be the most dominant sound radiation region on the airfoil section. The microphone array measurements revealed dominant contributions from the TE from 160 to at least 2500 Hz. The peak level of T...
Aerofoil trailing-edge noise prediction models for wind turbine applications
Wind Energy
This paper proposes a modified TNO model for the prediction of aerofoil trailing-edge noise for wind turbine applications. The capabilities of the current modified model and four variants of the TNO model are analysed through a comprehensive study which includes ten aerofoils and involves two different wind tunnels. Some of these aerofoils are used on modern large wind turbines. For the test cases considered, the Reynolds numbers are between 1.13 and 3.41 million, and the effective angles of attack are between-2.2 • and 13.58 •. The merit of a model is assessed by comparing two aspects of the numerically-predicted and the experimentally-measured sound pressure level spectra. The first aspect is the sound pressure level difference between two different aerofoils at similar lift coefficients within a certain frequency range (referred to as the delta noise). The second is the closeness of the predicted and measured sound pressure level spectra of the aerofoils in various flow configurations. From the baseline model, the current modified model is developed by deriving new formulations for the computation of the wall pressure fluctuation spectrum. This is achieved by using the approximate ratio of the normal Reynolds stress components for an anisotropic flow over a flat plate to estimate the vertical Reynolds stress component, and by introducing new stretching factors in the streamwise, vertical and spanwise directions to take the effects of turbulent flow anisotropy into account. Compared to the four TNO model variants tested, the current modified model has strong delta noise prediction ability, and is able to predict sound pressure level spectra which are more consistent and closer to measurements for the vast majority of aerofoils and flow conditions tested in the two wind tunnels. Copyright
Extensions and limitations of analytical airfoil broadband noise models
International Journal of Aeroacoustics, 2010
The present paper is a state-of-the-art of a special class of analytical models to predict the broadband noise generated by thin airfoils in a flow, either clean or disturbed. Three generating mechanisms are addressed, namely the noise from the impingement of upstream turbulence called turbulence-interaction noise, the noise due to the scattering of boundary-layer turbulence as sound at the trailing edge for an attached flow called trailing-edge noise, and the noise generated due to the formation of a coherent vortex shedding in the near wake of a thick trailing edge, called vortex-shedding noise. Different analytical models previously proposed for each mechanism are reviewed, as declinations of the same basic approach inherited from the pioneer work performed by Amiet in the seventies and based on an extensive use of Schwarzschild's technique. This choice is only an alternative to other models available in the literature and is made here for the sake of a unified approach. Issues dealing with the input data and related to the practical applications to fan noise predictions are rapidly outlined. The validity of the models is ckeched against dedicated experiments with thin airfoils and the limitations as the real configurations depart from the model assumptions are pointed out.
Numerical Investigation of Tonal Trailing-Edge Noise Radiated by Low Reynolds Number Airfoils
Applied Sciences
A high-fidelity computational analysis carefully validated against concurrently obtained experimental results is employed to examine self-noise radiation of airfoils at transitional flow regimes, with a focus on elucidating the connection between the unsteady behavior of the laminar separation bubble (LSB) and the acoustic feedback-loop (AFL) resonant interactions observed in the airfoil boundary layers. The employed parametric study examines AFL sensitivity to the changes in the upstream flow conditions and the airfoil loading. Implicit Large-Eddy Simulations are performed for a NACA-0012 airfoil in selected transitional-flow regimes for which experimental measurements recorded characteristic multiple-tone acoustic spectra with a dual ladder-type frequency structure. The switch between the tone-producing and no-tone-producing regimes is traced to the LSB size and position as a function of the flow Reynolds number and the airfoil angle of attack, and further substantiated by the lin...
A study on the prediction of aerofoil trailing-edge noise for wind-turbine applications
Wind Energy, 2016
This paper presents a comparative study between BPM (Brooks, Pope and Marcolini) and TNO (TNO Institute of Applied Physics) models for the prediction of aerofoil trailing-edge noise with particular emphasis on wind-turbine applications. In this work, two enhanced versions of the BPM model are proposed and their performances are compared against two recent anisotropic TNO models that require more detailed boundary-layer information than the BPM-based models. The two current enhanced models are denoted as BPMM-PVII and BPMM-BLkω, where the former uses a panel method with viscous-inviscid interaction implemented and the latter employs a two-dimensional Reynolds-averaged Navier-Stokes model for boundary-layer calculations. By comparing the predicted sound spectra with existing measurement data for seven different aerofoils tested in the current study, it is shown that the BPMM-PVII model exhibits superior results to those by the other models for most cases despite the simplicity without considering anisotropy. The BPMM-PVII model is then combined with Prandtl's nonlinear lifting-line theory to calculate and investigate three-dimensional rotor noise characteristics of an NREL UAE Phase-VI wind turbine. It is demonstrated that the current approach may provide an efficient solution for the prediction of rotor aerodynamics and noise facilitating industrial design and development for low-noise wind turbines.
This report concerns the research, design, implementation and application of an airfoil trailing-edge noise prediction tool in the development of new, quieter airfoil for largesize wind turbine application. The tool is aimed at enabling comparative acoustic performance assessment of airfoils during the early development cycle of new blades and rotors for wind turbine applications. The ultimate goal is to enable the development of quieter wind turbines by the Wind Energy Industry. The task was accomplished by developing software that is simultaneously suitable for comparative design, computationally efficient and user-friendly. The tool was integrated into a state-of-theart wind turbine design and analysis code that may be downloaded from the web, in compiled or source code form, under general public licensing, at no charge. During the development, an extensive review of the existing airfoil trailing-edge noise prediction models was accomplished, and the semi-empirical BPM model was selected and modified to cope with generic airfoil geometry. The intrinsic accuracy of the original noise prediction model was evaluated as well as its sensitivity to the turbulence length scale parameter, with restrictions imposed accordingly. The criterion allowed comparison of performance of both CFD-RANS and a hybrid solver (XFLR5) on the calculation of the turbulent boundary layer data, with the eventual adjustment and selection of the latter. After all the elements for assembling the method had been selected and the code specified, a collaboration project was made effective between Poli-USP and TU-Berlin, which allowed the seamless coupling of the new airfoil TE noise module, "PNoise", to the popular wind turbine design/analysis integrated environment, "QBlade". After implementation, the code calculation routines were thoroughly verified and then used in the development of a family of "silent profiles" with good relative acoustic and aerodynamic performance. The sample airfoil development study closed the initial design cycle of the new tool and illustrated its ability to fulfill the originally intended purpose of enabling the design of new, quieter blades and rotors for the advancement of the Wind Energy Industry with limited environmental footprint.
Acoustics, 2020
An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data; they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.