Akio Ochi

Validation of new CFD tool using Non-orthogonal Octree with Boundary-fitted Layer Unstructured Grid

This paper describes an introduction and validation results of a newly developed CFD tool, named “Cflow”, which consists of an automatic Cartesian based grid generator and a flow solver based on unstructured finite volume method for polyhedral element grid cells. To allow both automatic grid generation for highly complicated configurations and greater flexibility for high aspect ratio and sweptback wing configurations, Cflow employs “NOBLU (Non-orthogonal Octree with Boundary-fitted Layer Unstructured) Grid.” The grid generator of Cflow also equips feature lines preserving technique. The validation study of Cflow with NOBLU grid for high Reynolds number external flow over the ONERA M6 wing was conducted and showed good agreements with the experimental data. In addition, Cflow is applied to the NASA Common Research Model wing-body configuration. Cflow with NOBLU grid can generate a fair computational grid for such a high aspect ratio aircraft configuration and NOBLU grid proves the superiority over Cartesian based grid.

TAS Code, FaSTAR, and Cflow Results for the Sixth Drag Prediction Workshop

Three mixed-element unstructured Reynolds-averaged Navier–Stokes solvers, the TAS code, FaSTAR, and Cflow, were applied to the Sixth AIAA Drag Prediction Workshop test cases to investigate the accuracy of the solvers with committee-provided grids and custom participant-generated grids by MEGG3D, BOXFUN, and the Cflow built-in grid generator. Solutions were obtained for the verification study using the two-dimensional NACA 0012 airfoil (test case 1), the NASA common research model nacelle–pylon drag incremental study (test case 2), and the common research model wing/body static aeroelastic effect study (test case 3). In test case 1, the three solvers used the same turbulence model, the Spalart–Allmaras one-equation turbulence model without the trip term for transition and without the ft2 function, and their grid convergence trends for lift, drag, and pitching moment coefficients were similar to that of FUN3D, CFL3D, and TAU. In test case 2, the TAS code with the NASA GeoLab grids and with MEGG3D grids, FaS...

Summary of First Aerodynamics Prediction Challenge (APC-I)

A summary of First Aerodynamics Prediction Challenge (APC-I) is presented. The APC-I is a domestic CFD prediction workshop that was held in Japan on July 3, 2015. The test cases include verification benchmarks, aerodynamic prediction of NASA-CRM, and its wake flow prediction. One of the differences between APC-I and the previous Drag Prediction Workshop (DPW) is the inclusion of aeroelastic effects. We compare the CFD results with JAXA’s wind tunnel measurements. There were 14 participants from government, academia, industry, and commercial. The CFD results submitted from the participants are compared with the measurements, and emerged challenges are shown in this paper.

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.

2. Numerical simulation of flowfield around helicopter rotor by moving overlapped grid method

Flow around a complicated shape is very difficult because of the grid generation. In the present approach we used a Cartesian coordinate system with equal spacing for the three directions. Inside the body the velocity components are simply set to be zero. The Navier-Stokes equations are directly solved by a finite-difference method without using any turbulence model at Reynolds number 250 000. The number of the grid points is 64×257×129. The pressure distribution on the surface of the body and the ground is visualized by shading. Also the pressure contour lines in the central plane and in a plane perpendicular to the flow direction are drawn. The computation was performed on DEC alpha based single CPU personal computer ALEPH533.