Unsteady Flow Analysis of a Multi-Element Airfoil Using Lattice Boltzmann Method
AIAA Journal, Sep 1, 2012
ABSTRACT High-lift devices employed on modern aircraft are significant contributors to overall ai... more ABSTRACT High-lift devices employed on modern aircraft are significant contributors to overall airframe noise. In this paper, a lattice Boltzmann method with a very large eddy simulation approach is applied to computationally investigate the aerodynamic and aeroacoustic behavior of the flow around a generic high-lift configuration (three-element airfoil) at low Mach number. Three-dimensional time-dependent nearly incompressible simulations were conducted at different angles of attack to capture the instantaneous and mean flowfields around the airfoil, previously predicted by Navier Stokes studies. The computed mean flow results showed good agreement with existing experimental and numerical data, which include the pressure distributions around the elemental surfaces and the time-averaged mean flowfield within the slat cove. As a major objective of the present study, the unsteady flow simulations were used to capture the slat cove unsteadiness, a source of both broadband and narrowband noise. In particular, the effect of angle of attack on the shear layer emanating from the slat cusp, slat trailing-edge vortex shedding, convection, and reattachment of vortical structures near the slat gap were explored by the present simulations. Consequently, the acoustic implications of such complex unsteady flow phenomenon within the slat cove were explained and discussed in detail.
47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, Jan 5, 2009
Accurate prediction of unsteady flow phenomena and corresponding generation of tonal/broadband no... more Accurate prediction of unsteady flow phenomena and corresponding generation of tonal/broadband noise in turbomachinery applications is a challenging problem for existing numerical methods. In this study, a Lattice Boltzmann method (LBM) with a very large eddy simulation (VLES) approach is applied to computationally investigate the aerodynamic behavior of the flow around a generic Rod-Airfoil configuration, where both narrowband and broadband noise are generated during the interactions between the flow and the rodairfoil structure. Three-dimensional, time accurate, fully turbulent simulations are performed to capture the complex flow field in accordance with recent experiments conducted by Jacob et al. 1 As part of the benchmarking efforts, the mean and RMS flow fields, unsteady aerodynamics and acoustic far field results were compared with experiments. For the acoustic far field computation, a Ffowcs Williams Hawkings acoustics formulation was applied. Good agreement of the computed results with experimental data were obtained, which demonstrated the viability of the LBM-VLES/FWH coupling approach as a reliable tool for predictions of aerodynamics/aeroacoustics from complex flow fields. Nomenclature k turbulent kinetic energy
Towards Numerical Aircraft Noise Certification: Analysis of a Full-Scale Landing Gear in Fly-Over Configuration
This paper describes a numerical procedure for the prediction of aircraft noise certi cation metr... more This paper describes a numerical procedure for the prediction of aircraft noise certi cation metrics starting from the aircraft trajectory. The procedure is applied to the nose landing gear of a Gulfstream business jet. The numerical core of the procedure is a hybrid aeroacoustic method based on a lattice Boltzmann ow simulation and a Ffowcs-Williams & Hawkings noise propagation computation. The hybrid method is initially validated by computing the noise generated by a geometrically simpli ed model of the same landing gear installed on a at plate and comparing wall pressure and fareld noise spectra with wind-tunnel measurements. The same numerical method and a similar discretized model are then employed to compute the unsteady ow eld past the real landing gear deployed under the aircraft. The upstream ow conditions are the same occurring during a ight along a \nominally" constant descent trajectory at the nearest point to the ground microphone. Comparisons between the predicted noise levels and the measured ones during a ight test, with only the nose landing gear deployed and other airframe and engine sources kept at their admissible minimum, are in good agreement.
CFD/CAA Analysis of the LAGOON Landing Gear Configuration
The unsteady flow field about the ONERA/Airbus LAGOON two-wheel landing gear configuration and th... more The unsteady flow field about the ONERA/Airbus LAGOON two-wheel landing gear configuration and the associated aerodynamic noise generation are computed using a hybrid approach in which the flow field is provided by a Lattice-Boltzmann simulation, and the noise radiation is computed using the Ffowcs-Williams & Hawkings analogy. A detailed validation study is carried out, following the guidelines of the second workshop on benchmark problems for airframe noise computations, and deploying the complete experimental database for detailed comparisons. The effect of grid resolution on both nearand far-field results is investigated, showing the physical consistency of the numerical model. In addition, an assessment of the numerical prediction is carried out by computing the maximum perceived noise level along a nominal approach trajectory. Finally, an unsteady flow mechanism, never reported so far, involving the onset of cavity modes in the two facing rim cavities is analyzed in detail and correlated with the generation of tonal noise components.
Tandem Cylinder Noise Predictions Using Lattice Boltzmann and Ffowcs Williams-Hawkings Methods
Numerical simulations of tandem cylinder flow are performed using Lattice-Boltzmann method, for c... more Numerical simulations of tandem cylinder flow are performed using Lattice-Boltzmann method, for comparison with experimental data. This case is considered an aeroacoustics benchmark as it incorporates the key flow features and interactions present in more complex realistic ...
A hybrid approach to predict the far-field noise generated by an airplane nose landing gear is pr... more A hybrid approach to predict the far-field noise generated by an airplane nose landing gear is presented in this paper. The approach consists of a Lattice-Boltzmann Method (LBM) for the calculation of the flow-field around the fully detailed geometry of the landing gear which provides the input for a Ffowcs Williams-Hawkings (FW-H) solver to calculate the far-field noise. Both parts have been validated independently. The method is applied to the nose landing gear of a Gulfstream G550 business jet, for comparison with experimental results obtained in the University of Florida UFAFF wind tunnel. The near-field flow simulation using the LBM method showed good correlation with the PIV measurements of the flow field as well as surface microphone measurements, up to frequencies of about 4kHz. The comparison to experimental far-field results shows good agreement in the midfrequency range of 1-3kHz. At both low and high frequencies the simulations underpredict the measured results more strongly than the near field and surface measurements would suggest, which may be due to experimental limitations. A comparison between the solid and porous formulation of the FW-H solver shows that both method provide nearly equivalent results. However, inclusion of additional surfaces such as part of the fuselage is critical to achieving good results with the solid formulation. The effects of resolution of the near-field simulations are also investigated and show the expected lower cutoff frequency for lower resolutions for both the near-field and the far-field. No differences between the cases with different resolutions are observed up to 1 kHz in the near-field and up 2-3kHz in the farfield.
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Jan 4, 2011
Outlook-Hysteresis Effect-preliminary result Pitching TrapWing in WT α=28°-38°-28° in 1° steps In... more Outlook-Hysteresis Effect-preliminary result Pitching TrapWing in WT α=28°-38°-28° in 1° steps Initialized from steady 28° 0.05s per 1° (0.02s rotating & 0.03s settling) ~5days on 244CPUs
Simulation of Flow Over a 3-Element Airfoil Using a Lattice-Boltzmann Method
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
A Lattice-Boltzmann Method (LBM) based very large eddy simulation (VLES) approach is applied to s... more A Lattice-Boltzmann Method (LBM) based very large eddy simulation (VLES) approach is applied to simulate the flow field around a generic three-element airfoil. LBM describes a fluid flow in terms of a discrete kinetic equation based on the particle density distribution function (the Lattice Boltzmann equation). The effects of turbulence are modeled through an effective particle-relaxation-time scale in the extended kinetic equations. In the present study, 3D time-dependent simulations were conducted to capture the instantaneous and mean flow fields. The computed results provided good predictions of the mean flow field, which include the pressure distributions along the elemental surfaces and the time averaged mean flow field inside the slat cove. Typical unsteady flow features that characterize the shear layer emanating from the slat cusp, slat trailing edge vortex shedding, convection and reattachment of vortical structures near the slat gap were also well predicted by the present simulations.
A Lattice-Boltzmann Method (LBM) based Very Large-eddy Simulation (VLES) approach was used to stu... more A Lattice-Boltzmann Method (LBM) based Very Large-eddy Simulation (VLES) approach was used to study the near-field noise generation around a complex nose landing gear configuration. LBM describes a fluid flow in terms of discrete kinetic equation based on the particle density distribution function (the Lattice Boltzmann equation). The macroscopic flow properties are results of the moments of these particle density distribution functions. The e ects of turbulence are modeled using two transport equations based on a revised renormalization-group (RNG) theory, and realized through an e ective particle-relaxation-time scale in the extended kinetic equations. The flow solution is obtained on a Cartesian grid system that resolves the boundary geometry exactly. A three dimensional, unsteady, compressible flow simulation is conducted to capture the instantaneous flow-field that is responsible for the near-field noise generation around the gear assembly. It is found that the interaction between small details of the gear components and local flow tends to produce high level fluctuations in both the low and high frequency ranges, which, contribute significantly to the overall noise generation.
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Papers by Swen Noelting