Comparison of Rod-Airfoil Noise Calculation between Large Eddy Simulation (LES) and Detached-Eddy Simulation (DES) (original) (raw)
Related papers
Aerodynamic Noise Prediction for a Rod-Airfoil Configuration using Large Eddy Simulations
20th AIAA/CEAS Aeroacoustics Conference, 2014
Aerodynamic noise produced by aerodynamic interaction between a cylinder (rod) and an airfoil in tandem arrangement is investigated using large eddy simulations. Wake from the rod convects with the flow, impinges of the airfoil to produce unsteady force which acts as a sound source. This rod-airfoil interaction problem is a model problem for noise generation due to inflow or upstream-generated turbulence interacting with a turbomachine bladerow or a wind turbine rotor. The OpenFoam and Charles (developed by Cascade Technologies) solvers are chosen to carry out the numerical simulations. The airfoil is set at zero angle of attack for the simulations. The flow conditions are specified by the Reynolds number (based on the rod diameter), Red = 48 K, and the flow Mach number, M = 0.2. Comparisons with measured data are made for (a) mean and root-mean-squared velocity profiles in the rod and airfoil wakes, (b) velocity spectra in the near field, and (c) far-field pressure spectra and directivity. Near-field flow data (on-and off-surface) is used with the Ffowcs Williams-Hawkings (FW-H) acoustic analogy as well as Amiet's theory to predict far-field sound. Disciplines
Three-dimensional predictions of the rod wake-airfoil interaction noise by hybrid methods
2007
Sound generated by an airfoil in the wake of a rod is predicted numerically by two different hybrid CFD/CAA approaches (Ma = 0.2). The configuration is a symmetric airfoil one chord downstream of a rod, whose wake contains both periodic and broadband vortical fluctuations. In particular, a significant broadening of the main Strouhal peak has been observed at subcritical vortex shedding conditions. This study addresses the overall ability of both CFD/CAA hybrid approaches to model broadband noise sources. The first approach computes the aerodynamic noise by solving the linearized perturbed compressible equations (LPCE) for the noise propagation, with the acoustic sources and hydrodynamic flow variables computed from the incompressible Large Eddy Simulation (iLES) using a computional grid of approximately 3 million grid cells and high-order compact finite difference schemes. The second approach uses the unsteady aerodynamic field of a compressible Detached Eddy Simulation (DES) and a ...
Uncertainty quantification of the far-field noise from a rod-airfoil configuration
A Large-Eddy Simulation (LES) solver together with a Ffowcs-Williams and Hawking (FW-H) solver are coupled with a non-intrusive stochastic collocation method to propagate the geometric uncertainty observed in a rod-airfoil experiment. The LES are performed for several displacements of the rod with respect to its nominal position in the cross-wise direction. The positions are chosen to match the Clenshaw-Curtis (CC) points. The acoustic fields are obtained using an FW-H analogy on aerodynamic results sampled over the time on a porous surface embedded in the mesh. An uncertainty quantification is then performed on the mean and fluctuating root-mean-squared (rms) velocity at several transverse profiles, on the mean wall-pressure coefficient C p on the airfoil and on both the acoustic spectra and the directivity. The uncertainty of the rod position only partially recovers the discrepancies seen in the experimental data. An uncertainty in the position of the rod of ±0.004 m leads to an uncertainty of 0.5-1 dB in the Overall Sound Pressure Levels (OASPL).
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...
A rod-airfoil experiment as a benchmark for broadband noise modeling
Theoretical and Computational Fluid Dynamics, 2005
A low Mach number rod-airfoil experiment is shown to be a good benchmark for numerical and theoretical broadband noise modeling. The benchmarking approach is applied to a sound computation from a 2D unsteady-Reynolds-averaged Navier-Stokes (U-RANS) flow field, where 3D effects are partially compensated for by a spanwise statistical model and by a 3D large eddy simulation. The experiment was conducted in the large anechoic wind tunnel of the Ecole Centrale de Lyon. Measurements taken included particle image velocity (PIV) around the airfoil, single hot wire, wall pressure coherence, and far field pressure. These measurements highlight the strong 3D effects responsible for spectral broadening around the rod vortex shedding frequency in the subcritical regime, and the dominance of the noise generated around the airfoil leading edge. The benchmarking approach is illustrated by two examples: -the validation of a stochastical noise generation model applied to a 2D U-RANS computation; -the assessment of a 3D LES computation using a new subgrid scale (SGS) model coupled to an advanced-time Ffowcs-Williams and Hawkings sound computation. In both cases, the ability of computational fluid dynamics to model the source mechanisms and of the CAA approach to predict the far field are assessed separately.
Computation of unsteady flow and aerodynamic noise of NACA0018 airfoil using large-eddy simulation
International journal of heat and fluid flow, 2006
The flow field around a symmetrical NACA airfoil in the uniform flow under generation of noise was numerically studied. The numerical simulation was carried out by a large-eddy simulation that employs a deductive dynamic model as the subgrid-scale model. The results at small angle of attack a = 3-6°indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of pressure side and the strong instability thereafter affects positive vortices shed near the trailing edge. The quasiperiodic behavior of negative vortex formation on the suction side is affected by the strength and the periodicity of positive vortices near the trailing edge. The computation using aero-acoustic analogy indicates the primary discrete peak at the Strouhal frequency (=2f AE d/U 0) of 0.15 by the vortex shedding from the trailing edge, which is in a close agreement with the experiment.
International Journal of Aeroacoustics, 2010
A successful comparison between CFD-CAA and measurements of trailing edge noise is shown for a highly loaded and cambered NACA 5510 airfoil at a chord based Reynolds number of aprox. 1 million placed in a quiet low Mach number flow. The simulation is based on a new variant of the DES-the Improved Delayed Detached Eddy Simulation (IDDES). The flow is fully attached to the airfoil and therefore only the small turbulent boundary structures that interact with the trailing edge generate significant broadband noise in the far field. The IDDES approach is designed to extend the LES region of the original DES approach (hybrid RANS/LES) from Spalart et. al. (1997) to the turbulent boundary layer, as proposed first by Travin et. al. in 2006. The non-zonal blending occures therefore inside the boundary layerthe RANS model acts as a wall model for the LES. The actual work shows the capabilities of this novel approach for the simulation of broadband noise for attached flows. The simulation is compared to measurements from the EC Lyon including PIV and LDA data around the airfoil and unsteady on-wall pressure measurements near the trailing edge. Far field computations are carried out by applying the Ffowcs-Williams and Hawkings analogy to the unsteady wall pressure field and compared to acoustic measurements as well as to a far field prediction based on a trailing edge noise model that is applied to the experimental aerodynamic pressure field.
Noise Simulation around NACA0012 Wingtip using Large Eddy Simulation
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, 2012
Flow structures around a NACA0012 wingtip are investigated using a zonal LES/RANS hybrid method in order to understand the noise generation mechanism around the flap-edge. It is known from previous studies that the flow around a blunt wingtip is similar to that of the flap-edge. Grid dependency studies are performed for both time-averaged and unsteady components, and the results are assessed via comparison with the experimental data. It became apparent that the zonal LES/RANS hybrid results are more sensitive to the chordwise grid resolution, compared with these of RANS. Based on the validated data, the noise generation mechanism around the wingtip is discussed. The near-field flow structures relevant to noise generation are obtained successfully.