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Flow and noise predictions for the tandem cylinder aeroacoustic benchmarka)

Flow and noise predictions for the tandem cylinder benchmark are performed using lattice Boltzmann and Ffowcs Williams–Hawkings methods. The numerical results are compared to experimental measurements from the Basic Aerodynamic Research Tunnel and Quiet Flow Facility (QFF) at NASA Langley Research Center. The present study focuses on two configurations: the first configuration corresponds to the typical setup with uniform inflow and spanwise periodic boundary condition. To investigate installation effects, the second configuration matches the QFF setup and geometry, including the rectangular open jet nozzle, and the two vertical side plates mounted in the span to support the test models. For both simulations, the full span of 16 cylinder diameters is simulated, matching the experimental dimensions. Overall, good agreement is obtained with the experimental surface data, flow field, and radiated noise measurements. In particular, the presence of the side plates significantly reduces the excessive spanwise coherence observed with periodic boundary conditions and improves the predictions of the tonal peak amplitude in the far-field noise spectra. Inclusion of the contributions from the side plates in the calculation of the radiated noise shows an overall increase in the predicted spectra and directivity, leading to a better match with the experimental measurements. The measured increase is about 1 to 2 dB at the main shedding frequency and harmonics, and is likely caused by reflections on the spanwise side plates. The broadband levels are also slightly higher by about 2 to 3 dB, likely due to the shear layers from the nozzle exit impacting the side plates.

Unsteady Flow Simulation of a High-Lift configuration using a Lattice Boltzmann Approach

A Lattice-Boltzmann Method (LBM) based approach combined with a very large eddy simulation (VLES) turbulence modeling is used for the unsteady simulation of the flow field around the high-lift configuration used in the first AIAA high-lift prediction workshop. The numerical approach as well as the meshing technique is briefly described. The simulations are conducted first for some selected angle of attacks and configurations prescribed within the workshop and compared to the available experimental results. Several investigations are presented including a resolution study, the influence of added geometrical details and the laminar to turbulence transition in the simulation. In a second step the simulation domain is extended to include the wind tunnel walls in an effort to predict the blockage and installation effects of the wind tunnel and compare with the uncorrected force and moment measurements.

Simulation of Flow Over a 3-Element Airfoil Using a Lattice-Boltzmann Method

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.

Towards Lattice-Boltzmann Prediction of Turbofan Engine Noise

The goal of the present paper is to report verification and validation studies carried out by Exa Corporation in the framework of turbofan engine noise prediction through the hybrid Lattice-Boltzmann/Ffowcs-Williams & Hawkings approach (LB)-(FW-H). The underlying noise generation and propagation mechanisms related to the jet flow field and the fan are addressed separately by considering a series of elementary numerical experiments. As far as fan and jet noise generation is concerned, validation studies are performed by comparing the LB solutions with literature experimental data, whereas, for the fan noise transmission through and radiation from the engine intake and bypass ducts, LB solutions are compared with finite element solutions of convected wave equations. In particular, for the fan noise propagation, specific verification analyses are carried out by considering tonal spinning duct modes in the presence of a liner, which is modelled as an equivalent acoustic porous medium. Finally, a capability overview is presented for a comprehensive turbofan engine noise prediction, by performing LB simulation for a generic but realistic turbofan engine configuration.

Simulation of Wall Pressure Fluctuations on Simplified Automobile Shapes Using a Lattice Based Method

A comparison of experimental data and CFD simulation results of wall pressure fluctuations on simplified geometries that generate flow structures similar to an automobile are presented. The numerical results have been obtained using the commercial software PowerFLOW 3.4p4a. The simulation kernel of this software is based on the numerical scheme known as the Lattice Boltzmann Method (LBM), combined with an RNG turbulence model. This scheme accurately captures time-dependent aerodynamic behavior of high Reynolds number flows over complex geometries, together with the acoustics. The geometries considered for this study represent the green house and the side mirror of a car. Spectral analysis is performed on the simulation data and the results are compared to the experimental data. This comparison provides good correlation between the simulation and experiment, and demonstrates the capability of this numerical scheme in predicting turbulent fluctuations due to complex flow phenomena.Copyright

CFD/CAA Analysis of the LAGOON Landing Gear Configuration

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.

Unsteady Flow Predictions around Tandem Cylinders with Sub-Critical Spacing

In the quest to better understand landing gear noise sources, the complex unsteady flow around a simplified configuration of a Tandem Cylinder Arrangement is considered and investigated in the current study. Recent experiments from the Basic Aerodynamics Research Tunnel (BART) and Quiet Flow Facility (QFF) at NASA Langley Research Center have provided extensive aerodynamic and aeroacoustic measurements around Tandem Cylinders with Subcritical spacing, which can be used to validate Computational Fluid Dynamics codes. In this study, Lattice Boltzmann simulations with a very large eddy simulation (VLES) approach were performed around the tandem cylinder arrangement with sub-critical spacing using the commercially available CFD code, PowerFLOW 4.1. Timedependent, three-dimensional simulations with a limited span of six cylinder diameters were conducted to compute the mean and unsteady flow structure and validate computed data using experimental data. Further, an in-depth analysis of the associated aeroacoustics is planned for future work.

Unsteady Flow Computations and Noise Predictions on a Rod-Airfoil Using Lattice Boltzmann Method

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.

Unsteady Flow Simulation of High-Lift stall Hysteresis using a Lattice Boltzmann Approach

A Lattice-Boltzmann flow solver is used for the prediction of the unsteady flow field around the Trap Wing high–lift configuration used in the first High–Lift Prediction Workshop. The numerical approach and the meshing technique are briefly described. The simulation model includes the effects of wind tunnel walls, the geometries of the slat/flap brackets and the laminar to turbulent transitional regions. Simulation results are compared to the uncorrected force and moment wind tunnel measurements as well as the pressure distributions at various spanwise sections. The numerical approach is further developed to include a time varying angle of attack resembling the continuous measurements of increasing/decreasing incidence in the wind tunnel. This approach aims at investigating the hysteresis effects which were documented during measurements. The simulation predictions are compared to available measurements and the flow phenomena during the hysteresis effects are analyzed based on the simulated unsteady flow structures, particularly the stall behavior. Numerical predictions correctly capture the hysteresis effects around the stall region and are shown to be related to the interaction between the slat and main wing separations near the wing tip. The simulations furthermore indicate that a longer time period and dynamic modifications of the laminar regions during simulation may be needed to further improve quantitative predictions.

Simulation of an S-Duct Inlet Using the Lattice-Boltzmann Method

Unsteady computations are presented for a serpentine inlet duct (S-duct) configuration which was one of the test cases used in AIAA’s series of Propulsion Aerodynamic Workshops to assess the accuracy of computational fluid dynamics (CFD) tools for air breathing propulsion applications. The simulations employ the lattice Boltzmann solver PowerFLOW®. All computations are inherently unsteady and use a hybrid turbulence model specially adapted to the underlying lattice Boltzmann method. A baseline configuration of the S-duct is considered first, followed by a modified configuration for which the flow separation in the SDuct is supressed with an array of vortex generators. The simulation results are compared to a number of different experimental results, including static pressures along the walls of the SDuct and flow field measurements at the exit plane of the S-duct geometry. The simulation results generally compare well to the experimental results, and the ability of the vortex generators to suppress the flow separation is correctly predicted.