Namhun Lee

Performance Evaluation of Two-Equation Turbulence Models for 3D Wing-Body Configuration

Numerical simulations of 3D aircraft configurations are performed in order to understand the effects of turbulence models on the prediction of aircrafts aerodynamic characteristics. An in-house CFD code that solves 3D RANS equations and two-equation turbulence model equations are used. The code applies Roe’s approximated Riemann solver and an AF-ADI scheme. Van Leer’s MUSCL extrapolation with van Albada’s limiter is also adopted. Various versions of Menter’s k-ω SST turbulence models as well as Coakley’s q-ω model are incorporated into the CFD code. Menter’s k-ω SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared with computational results from the 3 rd AIAA CFD Drag Prediction Workshop. Numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared with computational results of the 2 nd AIAA CFD Drag Prediction Workshop. Aerodynamic characteristics as well as flow features are scrutinized with respect to the turbulence models. The results obtained from each simulation incorporating Menter’s k-ω SST turbulence model variations are compared with one another.

Flapping-Wing Fluid–Structural Interaction Analysis Using Corotational Triangular Planar Structural Element

In this paper, a triangular planar element is developed for a geometrically nonlinear structural analysis, which includes the drilling degrees of freedom using a corotational framework. Based on the assumptions of a small degree of strain and large displacement, the corotational framework allows an accurate geometrically nonlinear structural analysis. The presently improved corotational framework accommodates in-plane rotational behavior (that is, the drilling degrees of freedom) by using the corotational framework corresponding to a solidlike planar element. It focuses on triangular planar elements that will be useful for three-dimensional analysis using a reduced number of degrees while targeting a structure with a complex geometry, such as a flapping wing. Regarding the present analysis, validation by solving both static and time-transient problems is conducted. The fluid–structure interaction framework is then developed by using the present structural analysis. During this validation procedure, the pr...

A Computational Analysis for Flapping Wing by Coupling the Geometrically Exact Beam and Preconditioned Navier-Stokes Solution

In a flapping wing micro air vehicle (MAV), inspired by an organism of either insects or birds, flexibility of the wing structure induces a crucial effect upon the vehicle performance. Thus, in an analysis upon the flapping wing MAV, coupling between aerodynamics and structural dynamics considering the wing flexibility will be a critical component. This paper presents an accurate computational approach to simulate a flapping wing by coupling between CFD and CSD. Non-linear structural analysis based on the geometrically exact beam formulation was used. Such non-linear beam analysis was coupled with preconditioned Navier-Stokes solutions. For a grid deformation in the aerodynamic analysis, the mesh shearing methodology was used. A coupling between the structural and aerodynamic analyses was conducted by adopting the implicit coupling approach. After that, an aeroelastic analysis was performed and the results are compared with the experimental results. However, the flapping wing configuration is not slender in reality and their vein section geometry is complex generally. Thus, to consider those features, the finite element analysis, beam and shell, based on a co-rotational (CR) theory was developed in parallel. Currently, the CR beam analysis with a warping DOF was developed and validated by comparing it with NASTRAN in static condition.

Numerical analysis of the vortex induced vibration of the 2-D cylinder using dynamic deforming mesh

In this paper, numerical simulations are performed on the lock-in phenomena of vortex induced vibration(VIV) of a two dimensional cylinder. A deforming grid as well as a rigidly moving grid are used to simulate the movement of the cylinder. The grid deformation is accomplished by the linear spring analogy. Converged solutions, which are obtained by controling the grid size and the non-dimensional time step, are used for comparison and validation of the analysis results. Moreover, the efficiency and the accuracy of the coupling methods for fluid-structure interaction are examined.In this paper, numerical simulations are performed on the lock-in phenomena of vortex induced vibration(VIV) of a two dimensional cylinder. A deforming grid as well as a rigidly moving grid are used to simulate the movement of the cylinder. The grid deformation is accomplished by the linear spring analogy. Converged solutions, which are obtained by controling the grid size and the non-dimensional time step, are used for comparison and validation of the analysis results. Moreover, the efficiency and the accuracy of the coupling methods for fluid-structure interaction are examined.

Aerodynamic Performance Evaluation of 3D Aircraft Configurations by Turbulence Models

Numerical simulations of 3D aircraft configurations are performed in order to understand the effects that turbulence models have on the aerodynamic characteristics of an aircraft. An in-house CFD code that solves 3D RANS equations and 2-equation turbulence model equations is used for the study. The code applies Roe’s approximated Riemann solver and an AF-ADI scheme. Furthermore van Leer’s MUSCL extrapolation with van Albada’s limiter is adopted. Various versions of Menter’s k-omega SST turbulence models as well as Coakley’s q-omega model are incorporated into the CFD code. Menter’s k-omega SST models include the standard model, the 2003 model, the model incorporating the vorticity source term, and the model containing controlled decay. Turbulent flows over a wing are simulated in order to validate the turbulence models contained in the CFD code. The results from these simulations are then compared to computational results of the 3rd AIAA CFD Drag Prediction Workshop. Moreover, numerical simulations of the DLR-F6 wing-body and wing-body-nacelle-pylon configurations are conducted and compared to computational results of the 2nd AIAA CFD Drag Prediction Workshop. Especially, the aerodynamic characteristics as well as flow features with respect to the turbulence models are scrutinized. The results obtained from each simulation incorporating Menter’s k-omega SST turbulence model variations are compared with one another.Copyright