Shigeru Obayashi
Ames Research Center
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Featured researches published by Shigeru Obayashi.
Fluid Dynamics Conference | 1994
Shigeru Obayashi; Guru P. Guruswamy
New capabilities have been added to a Navier-Stokes solver to perform steady-state simulations more efficiently. The flow solver for solving the Navier-Stokes equations is completely rewritten with a combination of the LU-SGS (Lower-Upper factored Symmetric Gauss-Seidel) implicit method and the modified HLLE (Harten-Lax-van Leer-Einfeldt) upwind scheme. A pseudo-time marching method is used for the directly coupled structural equations to improve overall convergence rates for static aeroelastic analysis. Results are demonstrated for transonic flows over rigid and flexible wings.
AIAA/ASME/ASCE/AHS/ASC. Structures, structural dynamics, and materials conference | 1991
Shigeru Obayashi; Guru P. Guruswamy
Unsteady Navier-Stokes computations have been carried out for simulating transonic flows over a clipped delta wing undergoing oscillatory and ramp motions, including flexibility. The implicit upwind algorithm has been validated by comparing the solutions with experimental data for the oscillatory pitching motion cases. The numerical and experimental results agree well at moderate angles of attack, where a leading-edge vortex develops. The ramp motion cases have demonstrated the effects of unsteadiness of the flowfleld and structural flexibility on the wing responses. For the 10-deg ramp motion, a vortex breakdown is observed. The inviscid interaction with the shock wave plays an essential role in the process of the breakdown observed in the present calculation.
9th Computational Fluid Dynamics Conference | 1989
Shigeru Obayashi; Peter M. Goorjian
An improved streamwise upwind algorithm has been used to study conical flow fields. In the present method, additional terms have been introduced in the cross-flow direction to prevent solution decoupling in supersonic flows, and the local Mach number is taken into account in order to evaluate the rotated differencing. It is found that the formula captures oblique shock waves in the same manner as Roes (1986) formula, has good convergence properties, and accurately computes shear flows.
Flight Simulation Technologies Conference and Exhibit | 1990
Shigeru Obayashi; Guru P. Guruswamy; Peter M. Goorjian
A new streamwise upwind algorithm has been derived to compute unsteady flows with a moving grid system and applied to compute flows over oscillating wings at transonic Mach numbers. Comparisons have been made between results obtained from this upwind algorithm, using both temporally nonconservative- and conservative-implicit methods, with the results obtained from a central-difference method, and also with experimental data. The results show (1) the efficiency and practicality of the temporally nonconservative implicit solver and (2) the robustness and accuracy of the upwind method for unsteady computations compared to the central-difference method.
9th AIAA/ISSMO Symposium on Multidisciplinary Analysis and Optimization | 2002
Guru P. Guruswamy; Shigeru Obayashi
Multidisciplinary optimization is a key element of design process. To date multidiscipline optimization methods that use low fidelity methods are well advanced. Optimization methods based on simple linear aerodynamic equations and plate structural equations have been applied to complex aerospace configurations. However, use of high fidelity methods such as the Euler/ Navier-Stokes for fluids and 3-D (three dimensional) finite elements for structures has begun recently. As an activity of Multidiscipline Design Optimization Technical Committee (MDO TC) of AIAA (American Institute of Aeronautics and Astronautics), an effort was initiated to assess the status of the use of high fidelity methods in multidisciplinary optimization. Contributions were solicited through the members MDO TC committee. This paper provides a summary of that survey.
Archive | 1990
Peter M. Goorjian; Shigeru Obayashi
Improvements have been made to a streamwise upwind algorithm so that it can be used for calculating flows with vortices. A calculation is shown of flow over a delta wing at an angle of attack. The laminar, thin-layer, Navier-Stokes equations are used for the calculation. The results are compared with another upwind method, a central-differencing method, and experimental data. The present method shows improvements in accuracy and convergence properties.
23rd Fluid Dynamics, Plasmadynamics, and Lasers Conference | 1993
Eugene L. Tu; Shigeru Obayashi; Guru P. Guruswamy
A time-accurate thin-layer Navier-Stokes simulation of the unsteady flowfield is performed for a typical canard-wing-body configuration undergoing ramp motions. The computations are made at a transonic Mach number of 0.90 and for ramp angles from 0 to 15 degrees. Accuracy is determined by comparisons with steady-state experimental data and with spatial and time-step refinement studies. During the ramp motion, the computational results show improved dynamic lift performance and a strong canard-wing interaction for the canard-on configuration. Formation of the canard leading-edge vortex is inhibited in the early stages of the ramp motion. An analysis performed on the transient flowfield after the ramp motion ends shows that the canard vortex rapidly gains strength and vortex breakdown eventually occurs. These characteristics of the canard vortex have significant influences on wing performance.
Archive | 1991
Shigeru Obayashi; Guru P. Guruswamy; Eugene L. Tu
Archive | 1990
Shigeru Obayashi; Peter M. Goorjian; Guru P. Guruswamy
Guidance, Navigation and Control Conference | 1992
Shigeru Obayashi; Guru P. Guruswamy