Eiji Shima

Development of a High-Order Flux Reconstruction Scheme for Body-Fitted Cartesian Unstructured Grids

A high-order flux reconstruction (FR) scheme on unstructured hexahedral grids is developed for aerospace flow simulation. In order to use computational grids generated by the body-fitted Cartesian (BFC) method, the grid which contains polyhedral cells with hanging nodes are subdivide into hexahedral cells first. Then, to perform computation by the FR scheme on the non-conformal hexahedral grid, the mortal element method (MEM) is employed to determine the numerical flux at cell interface. As a shock capturing scheme, the localized artificial diffusivity (LAD) method is developed for the FR scheme. The developed scheme is tested for typical benchmark problems including smooth and shocked flows. I. Introduction HE use of CFD in designing aerospace vehicles has been growing over the past decades. Commercial CFD software can be effectively used for early stage of the design process with the reasonable accuracy in quick turn around time. The finite volume methods (FVM) are widely used for the commercial and industrial CFD solvers, but the spatial order of accuracy is remained less than 2 nd -order due to several reasons mainly related to the robustness. In order to tackle more complicated flowfields and to improve the prediction accuracy by CFD, employing highorder methods is one of the prospective directions. It is well known that high-order methods can give the numerical solution more efficiently than the low-order methods with the same level of accuracy if the flowfield is sufficiently smooth. High-order methods were developed and investigated first in the context of the structured or multi-block structured grids. The formal order of accuracy can be retained with the relatively better quality mesh in contrast to the case with unstructured grids. A main drawback with structured grids is the difficulty in the mesh generation around complex geometries. Therefore, unstructured methods are often used in the production codes. Automated processes in the unstructured grid generation has facilitated the routinely works in the design cycle and has gained more users in the wide engineering areas. A criticism for this approach is related to the solution accuracy especially on the dirty grid around real complicated configurations. Recent research for the reconstruction of the solution gradient

Assessment of an Unstructured CFD Solver for RANS Simulation on Body-Fitted Cartesian Grids

A cell-centered finite volume flow solver LS-FLOW that has been developed by JEDI/JAXA is applied to benchmark RANS simulations, and the solution accuracy and the computational efficiency are investigated. LS-FLOW can handle unstructured grids consisting of arbitrary polyhedral cells. A high-order flux reconstruction (FR) scheme on unstructured hexahedral grids has been developed and devised in LS-FLOW recently. The developed high-order unstructured grid solver is also assessed for the benchmark cases. Comparisons of the results obtained by the second order FVM and the higher-order FR method indicate that the FR solver can be competitive with the FVM in terms of the computational time by employing similar basic solution algorithms such as LU-SGS scheme for the same number of degrees of freedom, and also that the higher-order method can provide accurate result more efficiently for certain case of steady RANS simulation.

Aerodynamic Characteristics and Kinematic Analysis during Turnover of a Reusable Sounding Rocket

Flight capability of a reusable sounding rocket during turnover was investigated by numerical analysis. In this study, we first carried out the numerical flow simulation to obtain aerodynamic characteristics in turnover maneuver, and then solved kinematic equations of a rotating rigid body using obtained dynamic characteristics. Although the body for research is a simple baseline shape, and parts of aerodynamics, fins, strakes, canards and so on are not attached, simulated flow conditions are based on a real flight. From the results, we could evaluate basic flight capability of this rocket in turnover maneuver.

Parallel calculation of helicopter BVI noise by moving overlapped grid method

This chapter summarizes the progress of a prediction method of helicopter blade-vortex interaction (BVI) noise developed under the cooperative research between National Aerospace Laboratory (NAL) and Advanced Technology Institute of Commuter-helicopter, Ltd. (ATIC). This prediction method consists of an unsteady Euler code using a moving overlapped grid method and an aeroacoustic code based on the Ffowcs Williams and Hawking (FW-H) formulation. The present large-scale calculations are performed on a vector parallel super computer, Numerical Wind Tunnel (NWT), in NAL. Therefore, a new algorithm of search and interpolation suitable for vector parallel computations is developed for the efficient exchange of flow solution between grids. The calculated aerodynamic and aeroacoustic results are in good agreement with the experimental data obtained by ATIC model rotor test at German Dutch Windtunnel (DNW). The distinct spikes in the waveform of BVI noise are successfully predicted by the present method.