Einkeun Kwak

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.

Development of Aircraft Mission Performance Analysis Program

A general purpose aircraft mission performance analysis program has been developed. The program can be used in design mode or in analysis mode. Fuel weight for a given mission profile can be estimated when the design mode is chosen, while mission time or mission range for a given fuel can be estimated when the analysis mode is chosen. The mission analysis program is written with JAVA and includes GUI(Graphic User Interface) for users’ conveniences. With a proper combination of databases for propulsion, aerodynamics and weight, the program can be configured to compute the performance of any type of aircraft. The program is validated by comparing its results with the results of a well known performance analysis program by ADD(Agency for Defense Development)

Convergence Study of Inlet Buzz Frequency with Computational Parameters

Numerical simulations of inlet buzz are performed to find effects of computational parameters, i.e., the maximum limit of sub-iterations, the grid density, and the time-step size on buzz frequency. An axisymmetric supersonic external compression inlet is chosen as a simulation model. Simulations are carried out using an axisymmertic Reynolds-averaged Navier-Stokes solver with Menter’s  k  two-equation turbulence model. Convergence of the buzz frequency is systematically studied with the computational parameters. Through results of the study, proper computational parameters to obtain a converged buzz frequency are determined.

Development of an Off-line 6-DOF Simulation Program for Store Separation Analysis

Off-line 6-DOF simulation program for store separation analysis has been developed. The developed program enables to predict a trajectory of a store from the database which was constructed by wind tunnel testing or CFD analysis. The flow angle method was applied to the program for predicting aerodynamic coefficients from the database and the ejector forces and constraints were enabled to incorporate the equations of motion for computing the trajectory. Using the program, the trajectories were calculated and the results are compared with the CTS results.

Numerical Study of the Effect of Exit Configurations on Supersonic Inlet Buzz

Numerical simulations of flows around Nagashima et al.s supersonic inlet with three exit configurations are performed to determine the effects of exit configurations on inlet buzz. Two exits are axisymmetric configurations with different locations, and the other is a 3-D configuration exit with several holes. The supersonic inlet used in the simulations is an external compression type, and axisymmetric except the exit. Three-dimensional simulations are carried out using a Reynolds-averaged Navier-Stokes (RANS) solver with the SpalartAlmaras turbulence model. Results with two axisymmetric exit configurations indicate that the amplitude of the pressure oscillation and the dominant frequency are larger than those of the experimental data. On the other hand, the result with the 3-D configuration exit shows that both the pressure history and the dominant frequency are good agreement with experimental data.

Application of A Local Preconditioning Method for 3-D Compressible Low Mach Number Flows

Euler codes or Navier-Stokes codes for compressible flows suffer severe degradation in convergence as Mach number approaches zero. The convergence problem arose from the wide disparity in characteristic speeds can be solved using preconditioning methods without large modifications. In this paper, a preconditioned RANS(Reynolds Averaged Navier-Stokes) solver is developed for analysis of low Mach number flows. In order to validate the method, computational examples are chosen and the results are compared with the experimental data and the existing computed results showing a good accuracy and convergence characteristics for steady inviscid, laminar and turbulent flows at low Mach number.

Design and Analysis of Wing-Tip and Wing-Body Fairings

In this study, fairing configurations for an aircraft are designed and the aerodynamic analyses of the fairings are performed to find the best choice for the aircraft. Fairings considered are wing-tip fairing and wing-body fairing. Wing alone analyses are done for the wing-tip faring selection, while wing-body-tail analyses are done for the wing-body fairing selection. A 3-D RANS solver with Menter`s SST turbulence model are used for the aerodynamic analyses. The effects on the drag of the aircraft are examined by comparing the analysis results with and without the farings.

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

Artificial Compressibility Method and Preconditioning Method for Solving Two Dimensional Incompressibile Flow

In this study, two commonly used numerical methods for the analysis of incompressible flows (or low Mach number flows), Chorins’ artificial compressibility method and Wiess and Smith’s preconditioning method are compared. Also, the convergence characteristics of two methods are numerically investigated for two-dimensional laminar and turbulent flows. Although the two methods have similar governing equations, the eigensystems and other details are very different. The eigensystems of the artificial compressibility method and the preconditioning method are analytically examined. An artificial compressibility code that solves the incompressible RANS (Reynolds Averaged Navier-Stokes) equations is newly developed for the study. An artificial compressibility code and a well-verified existing low Mach number code uses Roe’s approximate Riemann solver in conjunction with a cell centered finite volume method. Using MUSCL extrapolation with nonlinear limiters, 2nd order spatial accuracy is achieved while maintaining TVD (total variation diminishing) property. AF-ADI (approximate factorization-alternate direction implicit) method is used to get the steady solution for both codes. Menter’s k–ω SST turbulence model is used for the analysis of turbulent flows. Navier-Stokes equations and the turbulence model equations are solved in a loosely coupled manner.Copyright