Richard Shock

Numerical study of flow past an impulsively started cylinder by the lattice-Boltzmann method

In this paper a systematic numerical study of flow past an impulsively started circular cylinder at low and moderate Reynolds numbers using a lattice-Boltzmann algorithmic approach is presented together with an extended volumetric boundary scheme. Results agree well with some well-known previous works. It is demonstrated that in the nearly incompressible limit, this approach is able to provide accurate direct numerical simulations of unsteady flows with curved geometry.

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.

Simulation of Flow over an Iced Airfoil by Using a Lattice-Boltzmann Method

A Lattice-Boltzmann Method (LBM) is presented and applied to simulate subsonic flow over a business-jet airfoil with ice accrued on its leading edge at several angles of attack. The effects of turbulence are modeled by using two transport equations based on a revised renormalization-group theory, and realized through an effective particle-relaxation-time scale in the extended kinetic equations. A wall-shear stress model is used to reduce the nearwall resolution requirement. Flow solutions were obtained on a Cartesian grid system that resolves the boundary geometry exactly. Results compare well with experimental measurements even at angles of attack near stall.

Lattice Boltzmann Simulations of the DLR -F4, DLR -F6 and Variants

The DLR-F4 and DLR-F6 are simplified wing and fuselage geometries which have been used in the past for validation of computational fluid dynamics (CFD) codes at three AIAA sponsored Drag Prediction Workshops. The objectives of these workshops were to evaluate the use of state-of-the-art computational methods in predicting aircraft forces and moments. The first workshop, held in 2001 used the DLR-F4 geometry, while the second and third workshops used the DLR-F6 geometry and included variants of the DLR-F6 with nacelles and an additional wing-body fairing (the FX2B fairing) to remove the separation at the wing-body junction. In this paper, lattice Boltzmann simulations of these geometries are performed using the commercially available CFD code, PowerFLOW 4.0. We compare overall lift and drag values, deltas between geometry variants, and surface pressure coefficients to the detailed sets of experimental data. Predicted flow structures are compared to experimental surface oil flows at the wing-body junction to show the effectiveness of the FX2B fairing.

Unsteady Flow Analysis of a Multi-Element Airfoil Using Lattice Boltzmann Method

High-lift devices employed onmodern aircraft are significant contributors to overall airframe noise. In this paper, a lattice Boltzmannmethodwith 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 andmeanflowfields 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-averagedmean 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.

LATTICE-BOLTZMANN SIMULATIONS OF FLOWS OVER BACKWARD-FACING INCLINED STEPS

The lattice-Boltzmann method (LBM) is used in conjunction with a very large-eddy simulation (VLES) turbulence modeling approach to compute separated flows over backward-facing steps at different wall inclination angles. The Reynolds number ReH based on the step height H and center-line velocity at the channel inlet ucl is 64 000. The expansion ratio of the outlet section to the inlet section of the channel is 1.48. Wall inclination angles α considered include 10°, 15°, 20°, 25°, 30° and 90°. The computed flow fields for different inclination angles of the step are assessed against the laser Doppler anemometry (LDA) measurements of Makiola [B. Makiola, Ph.D. Thesis, University of Karlsruhe (1992); B. Ruck and B. Makiola, Flow separation over the step with inclined walls, in Near-Wall Turbulent Flows, eds. R. M. C. So, C. G. Speziale and B. E. Launder (Elsevier, 1993), p. 999.]. In addition to validating the lattice-Boltzmann solution with the experiments, this study also investigates the effects of three dimensionality, the proximity of the inlet to the step, and the grid resolution on the quality of the predictions.

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.

Computational Analysis of a Wingtip Vortex in the Near-Field using LBM-VLES Approach

In recent years, the near-field flow behavior of the tip vortex originating from airfoils has been widely studied to provide insight into the complex physics governing the growth and propagation of wingtip vortices. For this purpose, extensive experiments on a semi-span NACA0012 airfoil were recently conducted in the low speed wind tunnel at NASA Ames Research Center to provide data for benchmarking CFD codes. In the current study, a Lattice Boltzmann Method based very large eddy simulation (LBM-VLES) approach was used to simulate flow past a semi-span NACA0012 airfoil with rounded wingtip. Timedependent, three-dimensional simulations were conducted to compute the span wise distribution of mean pressure coefficient and the mean velocity field distributions around the tip vortex region. The computed results for the mean flow field, including surface pressure distribution, flow field velocity through the vortex core, and the location of the vortex core were found to agree well with experimental data. Further, an in-depth analysis of the unsteady flow field and the comparison and validation of computational results for the Reynolds stress tensor 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.

Simulation of Turbulent Flow in a Cyclonic Separator with Lattice-Boltzmann Method

A Lattice-Boltzmann Method (LBM) based very large eddy simulation (VLES) approach is presented and applied to simulate unsteady turbulent flow simulation inside a cyclone separator. LBM describes a fluid flow in terms of a discrete kinetic equation based on the particle density distribution function. The macroscopic flow properties are direct results of the moments of these particle density distribution functions. The effects of sub-grid turbulence are modeled by using two transport equations based on a revised renormalization-group theory, and realized through an effective particle-relaxation-time scale in the extended kinetic equations. This LBM based description of turbulent fluctuation carries flow history and upstream information, and contains high order terms to account for the nonlinearity of the Reynolds stress, which make it suitable to simulate the highly anisotropic unsteady turbulent flow inside cyclone separator. A wall-shear stress model is also used to reduce the near-wall resolution requirement. Flow solutions were obtained on a Cartesian grid system that resolves the boundary geometry exactly. Results compare well with experimental measurements and N-S based RSM (Reynolds stress model) predictions