Broadband Trailing-Edge Noise Predictions| Overview of BANC-III Results
TL;DR: This documentation summarizes the results from workshop category 1 (BANC-III-1) which focuses on the prediction of broadband turbulent boundary-layer trailing-edge noise and related source quantities.
Abstract: The Third Workshop on Benchmark Problems for Airframe Noise Computations, BANC-III, was held on 14-15 June 2014 in Atlanta, Georgia, USA. The objective of this workshop was to assess the present computational capability in the area of physics-based prediction of different types of airframe noise problems and to advance the state-of-the-art via a combined effort. This documentation summarizes the results from workshop category 1 (BANC-III-1) which focuses on the prediction of broadband turbulent boundary-layer trailing-edge noise and related source quantities. Since the forerunner BANC-II workshop identified some room for improvements in the achieved prediction quality, BANC-III-1 relies on the same test cases, namely 2D NACA0012 and DU96-W-180 airfoil sections in a uniform flow. Compared to BANC-II particularly the scatter among predictions for the DU96-W-
180 test case could be significantly reduced. However, proposed adaptations of previously applied computational methods did not systematically improve the prediction quality for all requested parameters. The category 1 workshop problem remains a challenging simulation
task due to its high requirements on resolving and modeling of turbulent boundary-layer source quantities.
Citations
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TL;DR: In this paper, the authors discuss a hierarchy of numerical approaches that range from semi-empirical schemes that estimate the wall pressure spectrum using mean flow and turbulence statistics to high-fidelity unsteady flow simulations such as Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) that resolve the sound generation and scattering process based on the first-principles flow physics.
Abstract: When the pressure fluctuations caused by turbulence vorticity in the boundary layer are scattered by a sharp trailing edge, acoustic energy is generated and propagated to the far field. This trailing edge noise is emitted from aircraft wings, turbomachinery blades, wind turbine blades, helicopter blades, etc. Being dominant at high frequencies, this trailing-edge noise is a key element that annoys human hearing. This article covers virtually the entire landscape of modern research into trailing-edge noise including theoretical developments, numerical simulations, wind tunnel experiments, and applications of trailing-edge noise. The theoretical approach includes Green’s function formulations, Wiener–Hopf methods that solve the mixed boundary-value problem, Howe’s and Amiet’s models that relate the wall pressure spectrum to acoustic radiation. Recent analytical developments for poroelasticity and serrations are also included. We discuss a hierarchy of numerical approaches that range from semi-empirical schemes that estimate the wall pressure spectrum using mean-flow and turbulence statistics to high-fidelity unsteady flow simulations such as Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) that resolve the sound generation and scattering process based on the first-principles flow physics. Wind tunnel experimental research that provided benchmark data for numerical simulations and unravel flow physics is reviewed. In each theoretical, numerical, and experimental approach, noise control methods for mitigating trailing-edge noise are discussed. Finally, highlights of practical applications of trailing-edge noise prediction and reduction to wind turbine noise, fan noise, and rotorcraft noise are given. The current challenges in each approach are summarized with a look toward the future developments. The review could be useful as a primer for new researchers or as a reference point to the state of the art for experienced professionals.
66 citations
22 Jun 2015
TL;DR: The Benchmark for Airframe Noise Computations (BANC) has been initiated by the BECAN Technical Discussion Group under AIAA as discussed by the authors, which aims at evaluating numerical methods for the simulation of unsteady flows and aerodynamic noise radiated by airframe components such as airfoil trailing edges, landing gears and high lift devices.
Abstract: The Benchmark for Airframe Noise Computations (BANC) has been initiated by the BECAN Technical Discussion Group under AIAA. This continuous framework, mainly impulsed by NASA LaRC, aims at evaluating numerical methods for the simulation of unsteady flows and aerodynamic noise radiated by airframe components such as airfoil trailing edges, landing gears and high lift devices. In this context, eight test-cases are proposed, with problem statements relying on extended experimental databases. The 2-wheel LAGOON landing gear is one of them. Originally designed and tested in the homonym project funded by Airbus-France, it has a simplified shape, compatible with a wide range of numerical methods, although involving complex physics. This paper summarizes seven submissions that were presented in this category at the Third BANC Workshop in Atlanta in June 2014. Researchers employed various block-structured, unstructured and embedded Cartesian (“octree”) grids and large computational resources to simulate the flow and radiated noise. The solutions are compared against each other and with experimental data gathered in two Onera’s windtunnels, F2 for aerodynamic data and CEPRA19 for acoustic data. Overall, all simulations captured the main features of the unsteady flow and radiated noise, including cavity resonances occurring between the wheels. The acoustic spectra and directivity diagrams of overall sound pressure levels are in fair agreement with experiment, although a significant dispersion can be observed between all contributions.
54 citations
TL;DR: In this article, an improvement of the TNO model was proposed to predict the noise emission from aerofoil sections due to the interaction of the boundary layer turbulence with the trailing edge.
Abstract: The paper describes an improvement of the so-called TNO model to predict the noise emission from aerofoil sections due to the interaction of the boundary layer turbulence with the trailing edge. The surface pressure field close to the trailing edge acts as source of sound in the TNO model. It is computed by solving a Poisson equation which includes flow turbulence cross correlation terms. Previously published TNO type models used the assumption of Blake to simplify the Poisson equation. This paper shows that the simplification should not be used. We present a new model which fully models the turbulence cross correlation terms. The predictions of the new model are in better agreement with measurements of the surface pressure and far field sound spectra. The computational cost of the new model is only slightly higher than the one of the TNO model, because we derived an analytical solution for the turbulence cross correlation terms.
25 citations
01 Jan 2016
TL;DR: In this paper, an improvement of the TNO model was proposed to predict the noise emission from aerofoil sections due to the interaction of the boundary layer turbulence with the trailing edge.
Abstract: The paper describes an improvement of the so-called TNO model to predict the noise emission from aerofoil sections due to the interaction of the boundary layer turbulence with the trailing edge. The surface pressure field close to the trailing edge acts as source of sound in the TNO model. It is computed by solving a Poisson equation which includes flow turbulence cross correlation terms. Previously published TNO type models used the assumption of Blake to simplify the Poisson equation. This paper shows that the simplification should not be used. We present a new model which fully models the turbulence cross correlation terms. The predictions of the new model are in better agreement with measurements of the surface pressure and far field sound spectra. The computational cost of the new model is only slightly higher than the one of the TNO model, because we derived an analytical solution for the turbulence cross correlation terms.
24 citations
TL;DR: In this article, the authors used empirical wall-pressure spectrum models to predict airfoil turbulent boundary-layer trailing edge noise using empirical wall pressure spectrum models and showed that these models can be used to predict the boundary layer noise.
Abstract: This paper presents the predictions of airfoil turbulent boundary-layer trailing-edge noise using empirical wall-pressure spectrum models. Five empirical wall-pressure spectrum models were used. In...
23 citations
References
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TL;DR: In this paper, two new two-equation eddy-viscosity turbulence models are presented, which combine different elements of existing models that are considered superior to their alternatives.
Abstract: Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-ω model of Wilcox in the inner region of the boundary layer and switches to the standard k-e model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity
15,459 citations
TL;DR: In this article, a CFD strategy is proposed that combines delayed detached-eddy simulation (DDES) with an improved RANS-LES hybrid model aimed at wall modelling in LES (WMLES).
Abstract: A CFD strategy is proposed that combines delayed detached-eddy simulation (DDES) with an improved RANS-LES hybrid model aimed at wall modelling in LES (WMLES). The system ensures a different response depending on whether the simulation does or does not have inflow turbulent content. In the first case, it reduces to WMLES: most of the turbulence is resolved except near the wall. Empirical improvements to this model relative to the pure DES equations provide a great increase of the resolved turbulence activity near the wall and adjust the resolved logarithmic layer to the modelled one, thus resolving the issue of “log layer mismatch” which is common in DES and other WMLES methods. An essential new element here is a definition of the subgrid length-scale which depends not only on the grid spacings, but also on the wall distance. In the case without inflow turbulent content, the proposed model performs as DDES, i.e., it gives a pure RANS solution for attached flows and a DES-like solution for massively separated flows. The coordination of the two branches is carried out by a blending function. The promise of the model is supported by its satisfactory performance in all the three modes it was designed for, namely, in pure WMLES applications (channel flow in a wide Reynolds-number range and flow over a hydrofoil with trailing-edge separation), in a natural DDES application (an airfoil in deep stall), and in a flow where both branches of the model are active in different flow regions (a backward-facing-step flow).
1,543 citations
01 Jul 1989
TL;DR: In this article, a prediction method for the self-generated noise of an airfoil blade encountering smooth flow was developed for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements.
Abstract: A prediction method is developed for the self-generated noise of an airfoil blade encountering smooth flow. The prediction methods for the individual self-noise mechanisms are semiempirical and are based on previous theoretical studies and data obtained from tests of two- and three-dimensional airfoil blade sections. The self-noise mechanisms are due to specific boundary-layer phenomena, that is, the boundary-layer turbulence passing the trailing edge, separated-boundary-layer and stalled flow over an airfoil, vortex shedding due to laminar boundary layer instabilities, vortex shedding from blunt trailing edges, and the turbulent vortex flow existing near the tip of lifting blades. The predictions are compared successfully with published data from three self-noise studies of different airfoil shapes. An application of the prediction method is reported for a large scale-model helicopter rotor, and the predictions compared well with experimental broadband noise measurements. A computer code of the method is given.
799 citations
01 Aug 1998
TL;DR: In this article, sound generation in a fluid with rigid and flexible boundaries has been studied, and the interaction of sound with solid structures has also been studied in the context of sound synthesis in unbounded flows.
Abstract: Preface 1. Introduction 2. Aerodynamic sound in unbounded flows 3. Sound generation in a fluid with rigid boundaries 4. Sound generation in a fluid with flexible boundaries 5. Interaction of sound with solid structures 6. Resonant and unstable systems References.
737 citations
Book•
13 Aug 1998TL;DR: In this article, sound generation in a fluid with rigid and flexible boundaries has been studied, and the interaction of sound with solid structures has also been studied in the context of sound synthesis in unbounded flows.
Abstract: Preface 1. Introduction 2. Aerodynamic sound in unbounded flows 3. Sound generation in a fluid with rigid boundaries 4. Sound generation in a fluid with flexible boundaries 5. Interaction of sound with solid structures 6. Resonant and unstable systems References.
712 citations