Keiichiro Fujimoto

New Gradient Calculation Method for MUSCL Type CFD Schemes in Arbitrary Polyhedra

The gradient calculation in the reconstruction phase is the key for the spatial accuracy and robustness of MUSCL type CFD schemes. For the gradient calculation, which bears central role in the second order reconstruction, new method for arbitrary polyhedra based on WLSQ (weighted least square) method merging the benefit of G-G (Green-Gauss) method is presented. The method, named GLSQ (G-G based WLSQ), has second order spatial accuracy for non-orthogonal and non-uniform linear mesh and gives rigorous gradient for thin curved mesh for which LSQ shows huge error. A new geometrical monotonicity condition, which gradient calculation method should satisfy for robustness, is also introduced. Although GLSQ is originally developed for hybrid meshes that combines octree and layered meshes, it is shown numerically that it also has better accuracy in usual rectangle and triangle meshes.

Study on the Automated CFD Analysis Tools for Conceptual Design of Space Transportation Vehicles

In order to improve turnaround time and usability of the aerodynamic analysis tool such as for the conceptual design of space launch vehicles, an automated high fidelity numerical aerodynamic analysis method is developed. This method has capability of fully automated and quick execution from geometry modeling through flow computation for high Reynolds number viscous flow over complicated geometry. The present method is based on the locally-body-fitted Cartesian grid method, which is applicable for the viscous flow computation over the complicated geometry and is easy-to-use requiring less expertise. Since this grid generation method has not been established due to the lack of robustness for feature preserving technique, robust feature preserving technique is developed in this study. In addition, the present method is validated and its prediction capability is confirmed through the application to the typical test problems including transonic airfoil flows, supersonic hemisphere flows, and subsonic/supersonic separated flow over the Apollo capsule. Finally, the proposed aerodynamic analysis method is applied to an aerodynamic analysis of aerodynamic fin effect on the single-stage-to-orbit (SSTO) rocket vehicle.© 2007 ASME

Numerical and Experimental Investigations of Epsilon Launch Vehicle Aerodynamics at Mach 1.5

The Epsilon launch vehicle, successor of the M-V rocket, which conveyed “Hayabusa” is currently under development in Japan. The Epsilon is also designed for sending scientific satellites to outer space, and its first flight is scheduled to be in 2013. In this study, by conducting both numerical simulations and wind-tunnel tests, the aerodynamic characteristics and associated flow features of the Epsilon launch vehicle are extensively investigated at Mach 1.5. The results provided are axial/normal/side forces, pitching/yawing/rolling moments, detailed three-dimensional flow structure, along with effects of the Reynolds number (between wind-tunnel and flight conditions), skin stringers (small devices on the main body), and the difference from another configuration called “NextGenEpsilon”. This set of data includes unavailable ones at either the experiment standalone or the actual flight. Magnitudes of computed aerodynamic coefficients are in good agreement with the experiment and within the design criteria....

Performance of low-dissipation euler fluxes and preconditioned implicit schemes in low speeds

In low speed flow computations, compressible finite-volume solvers are known to a) fail to converge in acceptable time and b) reach unphysical solutions. These problems are known to be cured by A) preconditioning on the time-derivative term, and B) control of numerical dissipation, respectively. There have been several methods of A) and B) proposed separately. However, it is unclear which combination is the most accurate, robust, and efficient for low speed flows. We carried out a comparative study of several well-known or recentlydeveloped low-dissipation Euler fluxes coupled with a preconditioned LU-SGS (LowerUpper Symmetric Gauss-Seidel) implicit time integration scheme to compute steady flows. Through a series of numerical experiments, accurate, efficient, and robust methods are suggested for low speed flow computations.

Computational aerodynamic analysis of capsule configurations toward the development of reusable rockets

Flowfields around Apollo-type conical configurations are numerically simulated by Reynolds-averaged Navier-Stokes computations at a wide range of angles of attack under subsonic through supersonic flows. Effects of the configuration parameters on the aerodynamic characteristics and their flow mechanisms were clarified based on the computed results. It turns out that the aerodynamic characteristics are mainly influenced by the separation position of the flow, the pressure level behind the body, and the wind-side high pressures. The shoulder radius has a great influence on the pressure level behind the body and the separation position, so that the aerodynamic characteristics, especially at base-first conditions, significantly change. The drag coefficient at base-first conditions becomes small for configuration with the large shoulder radius because of the increase of the lee-side pressure level. At both nose-first and base-first conditions, the fineness ratio has great influence on the location and the pressure level of the wind-side high pressures, which appear on the windward cone part, so that the lift, drag, and pitching-moment coefficients significantly change.

Compressible Flow Simulations Over Basic Reusable Rocket Configurations

Compressible flow around the basic reusable rocket configurations are numerically simulated by Navier-Stokes computations. The study started with the simulations of Apollo configuration to validate the simulation method by the comparison of the aerodynamic data with NASA’s experiments, and the capability of CFD estimation are discussed. Computed aerodynamic coefficients for the Apollo agreed well with the experiments at subsonic to supersonic flow regime for whole angle of attack range. Then, the effects of the configuration parameters on the aerodynamic characteristics are numerically investigated and clarified in detail. It turns out that the aerodynamic characteristicsismainlyinfluenced by the separating position of the flow, shock wave on the surface and the pressure level behind the body. Large shoulder radius causes the strong Mach number dependency of the aerodynamic characteristics, and large fineness ratio strongly influences to the (CL )max .Copyright

Numerical Flow Simulation of a Reusable Sounding Rocket during Turnover

Aerodynamic characteristics of a reusable sounding rocket are investigated by numerical flow simulation. Especially, we focus on the dynamic analysis during turnover. Here, a turnover corresponds to the motion from a gliding attitude to a vertical landing one during return to the earth. The numerical code for this study is based on a cell-centered finite volume compressible flow solver including a moving grid system. In order to treat an unsteady and massive separated flow, a DDES turbulence model is applied to this simulation. From the results of static and dynamic analyses , we could confirm the effect of rotational speeds and Reynolds number on aerodynamic characteristics.

Improvements in the Reliability and Efficiency of Body-fitted Cartesian Grid Method

In order to improve efficiency of the body-fitted Cartesian grid method and to make it possible to apply a geometry which includes complicated features such as small gaps, an extruded ghost surface is utilized. In the proposed approach, the grid front is generated by Cartesian grid generation over the ghost surface instead of the near-surface cell removal, which results in the faster turnaround and the flexibility to handle complicated geometry. By controlling length of an extrusion displacement vector, layer grid thickness, and by controlling grid resolution in a effective way such as sphere-type sources, an arbitrarily-shaped grid front can be obtained. As a result of this flexible capability to generate the arbitrarily-shaped grid front, body-fitted Cartesian grid method has been successfully extended to handle narrow gap problems.

Uncertainty Quantification for Destructive Re-Entry Risk Analysis: JAXA Perspective

In order to improve the accuracy of the expected casualty risk prediction for the destructive re-entry, the related uncertainty factors are identified and the uncertainty quantification approach are proposed. Based on our studies and experience, the identified dominant uncertainty factors are the model accuracy, the attitude stability mode, the shape complexity and shape change, and the initial conditions at the entry start and the break-up. High-fidelity numerical simulations play the important role to model complex multi-disciplinary physics and to cover the wide range of environmental conditions with small numbers of model validation data. The real shape and the deformation effects are initialy modeled by the high-fidelity numerical simulations and finally modeled by the reduced empirical physics-based models. Flight data acquisition also plays important the role to quantify the uncertainties of the attitude stability mode, the break-up altitude, and the temperature distributions and to validate the integrated risk analysis model. Some of the key findings obtained by the high-fidelity simulation are discussed. It is also shown that various types parameter dependencies such as Mach number, wall temperature, surface curvature, and the effect of the turbulent flows on the aerodynamic characteristics and the heat flux distributions should be considered in the empirical models.

VISUALIZATION AND VERIFICATION METHOD FOR FAILURE NETWORK ANALYSIS OF SPACE LAUNCH VEHICLES

Comprehensive failure network analysis method was studied for liquid rocket engine development which includes failure propagation through various types of component interfaces in order to achieve exhaustive enumeration of possible failures and to identify actions to eliminate or reduce the potential failure. New failure network visualization method was developed in order to make it easier to understand complicated failure propagation mechanism among multiple system levels. Verification analysis method is developed in which it is verified all of user-specified component interfaces are contained in the failure network analysis result. The perceived component interface is specified by the analyzer and the failure propagation in the result of failure analysis is summarized in two separate N2 charts. By comparing with these two N2 charts, unperceived component interface and the unconsidered failure propagation can be found. It is found to be promising approach to achieve exhaustive enumeration especially for forgettable component interface.Copyright