Surface Integral Analogy Approaches to Computing Noise Generated by a 3D High-Lift Wing Configuration

Three surface integral approaches of the acoustic analogies are studied to predict the noise from a three-dimensional, high-lift wing configuration. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings method of the permeable integral surface and the Curle method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specifically from the pressure perturbation on the wall. A new way to construct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex objective – the actual wing with high-lift devices – the integral surface based on the vorticity is constructed to follow the flow structures. The noise from the core flow region is based on the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FWH formulation. The role of each wall component on noise contribution is analyzed using the Curle method. The results of the three methods are then compared

Nonlinear subgrid-scale models for large-eddy simulation of rotating turbulent flows

We aim to design subgrid-scale models for large-eddy simulation of rotating turbulent flows. Rotating turbulent flows form a challenging test case for eddy viscosity models due to the presence of the conservative Coriolis force. We therefore propose a new subgrid-scale model that, in addition to a dissipative eddy viscosity term, contains a nondissipative nonlinear model term that can capture transport processes, such as those due to rotation. We show that the addition of this nonlinear model term leads to improved predictions of the Reynolds stress anisotropy in large-eddy simulations of a spanwise-rotating plane-channel flow, while maintaining the prediction of the mean velocity profile that is obtained when only using an eddy viscosity model.<br/

Assessment of high-lift concepts for a regional aircraft in the ALONOCO project

This work introduces the work conducted in the EU JTI project ANOLOCO, which has aimed at an assessment of aerodynamic and aeroacoustic performance of several high-lift configurations of a regional aircraft. The high-lift designs are for a laminar and slat-less wing, including configurations with a double slotted flap, single slotted flap, drooped nose and a Krueger flap. The aerodynamic performance is assessed from steady state RANS calculations up to maximum lift. The aeroacoustic performance is based on hybrid RANS-LES calculations for flow-induced noise generation, and using acoustic analogy methods for far-field noise propagation. Three different analogy methods are evaluated and compared. The assessment shows that the configuration with a Krueger flap gives the best performance. The maximum lift is close to 20% higher than for any other configuration and the noise levels are also reduced, up to 10 dB lower than the configuration with a double slotted flap

Surface integral analogy approaches for predicting noise from 3D high-lift low-noise wings

Three surface integral approaches of the acoustic analogies are studied to predict the noise from three conceptual configurations of three-dimensional high-lift low-noise wings. The approaches refer to the Kirchhoff method, the Ffowcs Williams and Hawkings (FW-H) method of the permeable integral surface and the Curle method that is known as a special case of the FW-H method. The first two approaches are used to compute the noise generated by the core flow region where the energetic structures exist. The last approach is adopted to predict the noise specially from the pressure perturbation on the wall. A new way to construct the integral surface that encloses the core region is proposed for the first two methods. Considering the local properties of the flow around the complex object-the actual wing with high-lift devices-the integral surface based on the vorticity is constructed to follow the flow structures. The surface location is discussed for the Kirchhoff method and the FW-H method because a common surface is used for them. The noise from the core flow region is studied on the basis of the dependent integral quantities, which are indicated by the Kirchhoff formulation and by the FW-H formulation. The role of each wall component on noise contribution is analyzed using the Curle formulation. Effects of the volume integral terms of Lighthill\u27s stress tensors on the noise prediction are then evaluated by comparing the results of the Curle method with the other two methods

Algebraic Reynolds stress modeling of turbulence subject to rapid homogeneous and non-homogeneous compression or expansion

A recently developed explicit algebraic Reynolds stress model (EARSM) by Grigoriev et al. ["A realizable explicit algebraic Reynolds stress model for compressible turbulent flow with significant mean dilatation," Phys. Fluids 25(10), 105112 (2013)] and the related differential Reynolds stress model (DRSM) are used to investigate the influence of homogeneous shear and compression on the evolution of turbulence in the limit of rapid distortion theory (RDT). The DRSM predictions of the turbulence kinetic energy evolution are in reasonable agreement with RDT while the evolution of diagonal components of anisotropy correctly captures the essential features, which is not the case for standard compressible extensions of DRSMs. The EARSM is shown to give a realizable anisotropy tensor and a correct trend of the growth of turbulence kinetic energy K, which saturates at a power law growth versus compression ratio, as well as retaining a normalized strain in the RDT regime. In contrast, an eddy-viscosity model results in a rapid exponential growth of K and excludes both realizability and high magnitude of the strain rate. We illustrate the importance of using a proper algebraic treatment of EARSM in systems with high values of dilatation and vorticity but low shear. A homogeneously compressed and rotating gas cloud with cylindrical symmetry, related to astrophysical flows and swirling supercritical flows, was investigated too. We also outline the extension of DRSM and EARSM to include the effect of non-homogeneous density coupled with "local mean acceleration" which can be important for, e.g., stratified flows or flows with heat release. A fixed-point analysis of direct numerical simulation data of combustion in a wall-jet flow demonstrates that our model gives quantitatively correct predictions of both streamwise and cross-stream components of turbulent density flux as well as their influence on the anisotropies. In summary, we believe that our approach, based on a proper formulation of the rapid pressure-strain correlation and accounting for the coupling with turbulent density flux, can be an important element in CFD tools for compressible flows.QC 20160314. QC 20160704</p

Airframe Noise Reduction Technologies Applied to High-Lift Devices of Future Green Regional Aircraft

International audienceIn the framework of CS-GRA ITD Project the acoustic impact of several high-lift devices (HLDs) and relevant low-noise technologies have been numerically and experimentally assessed toward their application to future regional aircraft for airframe noise reduction.CIRA designed an innovative “lined” flap, conceived as multi-layer structure with micro-perforation on the external sheet. The design was performed through an evolutionary algorithm that drives a FEM model of the acoustic field supported by analytical/empirical models for trailing-edge noise source estimation and liner impedance parameterization. The optimization of constructive liner parameters provided maximum noise reduction of about 6 dB along a downward radiation arc. CIRA also designed and numerically assessed three types/sizes of flap side-edge fences.Experimental investigations/validation of the above low-noise concepts were carried out through 2D WT tests at INCAS in collaboration with CIRA. Microphones array and the beam forming technique allowed assessing potential noise reduction of these technologies.ONERA numerically assessed an optimal distribution of absorbing liners for slat noise reduction. The aeroacoustic analysis was obtained through a ZDES approach for noise sources computation and a FW-H solver for acoustic propagation. The study showed liners providing noise reduction up to 5 dB along a downward radiation arc. Liners characteristics were delivered by tests in a specific bench, taking into account grazing flow.FOI and Chalmers carried out in project ALONOCO (CfP JTI-CS-2009-01-GRA-02-001) CFD/CAA 3D analyses of wing multi-body configurations with different HLDs. The aeroacoustic assessment was based on hybrid RANS-LES calculations for flow-induced noise generation and acoustic analogy methods for far-field noise propagation. Aerodynamic performance evaluation came from steady-state RANS solutions. Computations showed that configuration combining Krueger and flap gives best aerodynamic performance with maximum lift increasing of 20% and noise level reduced up to 10 dB, when compared at same lift coefficient, with respect to flap-only configurations.FOI and Chalmers numerically assessed in project CALAS (CfP JTI-CS-2011-03-GRA-02-018) a flap side-edge fence on a three-component wing. The modeling of noise source was supported with a Stochastic Noise Generation and Radiation method based on RANS solutions, and the far-field noise level was predicted with a BEM solver. The analysis showed that the fence enables overall noise reduction of about 5-8 dB.ONERA explored a multi-objective optimization of the slat position with respect to the main body of a conventional three-element wing configuration. The optimization approach, based on surrogate models, showed slat noise reduction of about 70% with aerodynamic performance also improved