Fumiya Togashi

Intergrid-Boundary Definition Method for Overset Unstructured Grid Approach

The use of the overset concept for the unstructured grid method is relatively unexplored. However, the overset approach can extend the applicability of the unstructured grid method for real engineering problems without much need for code development. The multiple moving-body problem is one of those applications. Improvement in local resolution for Euler/Navier-Stokes computations on unstructured grids is another use of the overset concept. An efficient and robust algorithm to localize the intergrid boundaries for the overset unstructured grid method is proposed. Simplicity and automation in the intergrid-boundary definition are realized using the wall distance as a basic parameter. The neighbor-to-neighbor jump search algorithm is efficiently utilized in the method. The robustness and efficiency of the search is improved by the use of subsidiary grids that are generated as a byproduct of the Delaunay triangulation method. The basic procedure of the present method is described for a multielement airfoil problem. The effects of the overset method on the solution accuracy and the convergence are tested by ONERA M6-wing

Flow simulation of NAL experimental supersonic airplane/booster separation using overset unstructured grids

Abstract The overset unstructured grid method developed for multiple-body problems is applied to a flow simulation about an experimental supersonic airplane separation from a rocket booster. An unstructured grid around the rocket booster is overset on the stationary grid around the airplane and moves with time to simulate the separation process. Detailed components of the rocket booster are faithfully reproduced by the unstructured grid. This capability of the unstructured grid reduces the number of required overset grids and significantly simplifies the overset procedure. The computed result of the airplane/booster separation clearly simulates the complex reflection patterns of shock waves between two bodies during the separation process. The computed lift and pitching moment coefficients are compared with the wind tunnel results. The computational accuracy of the aerodynamic coefficients is improved by including the detailed components of the airplane and rocket.

Numerical Simulations on Separation of Scaled Supersonic Experimental Airplane from Rocket Booster at Supersonic Speed

The present paper describes the numerical methods to compute flows around the NAL Scaled Supersonic Airplane in ascending flight and its separation process from the rocket booster. The Euler equations are solved on unstructured tetrahedral grid. A seamless procedure from CAD data to grid generation is developed to treat the complex configuration of the NAL airplane piggybacked on a rocket for ascending flight. The separation process of the airplane from the rocket is efficiently simulated by the overset unstructured grid method. Comparisons of the computed results with the experiments show good agreements in the lift and pitching moment histories. It is also shown that the small parts attached between the rocket and the airplane significantly change the aerodynamic coefficients of the airplane at transonic regime.

Simulation of Aircraft Response to Control Surface Deflection Using Unstructured Dynamic Grids

The computational techniques required for flight-test simulation in which the deflection angle of a tail wing is changed are discussed. To treat the computational grid for a moving control surface, an unstructured dynamic mesh method with surface-grid movement is used. This method is applied to the numerical simulation of the control-surface response for an experimental supersonic airplane at the National Aerospace Laboratory of Japan. Its high capability is demonstrated in both steady and unsteady simulations.

Extensions of Overset Unstructured Grids to Multiple Bodies in Contact

The overset unstructured grid method is extended to multiple bodies that are in contact with each other, and the treatment of nodes in the overlapping regions of two bodies in contact is discussed in detail. The developed overset unstructured grid method is applied to the following cases: ONERA M5 body/wing, ONERA M6 store separation, and the National Aeronautical Laboratory (NAL) experimental supersonic airplane/booster separation. In each case, there are two bodies in contact, and the calculation is performed with the Euler code

Overset Unstructured Grids Method for Viscous Flow Computations

Overset Unstructured Grids method is extended to the viscous flow computations of the multiple bodies in contact. In this paper, the overset treatment of hybrid meshes composed of tetrahedral , prismatic, pyramidal elements . is discussed in detail when those elements are embedded or contac ted to the wall boundary of another grid. This method is applied to the ONERA M5 wing -body model and computed by the Navier -Stokes code. The computational results show good agreements with those obtained by single grid and experimental data. The boundary l ayer in the intersection region between two grids is well captured without the collar grid.

Numerical Simulation of H 2 /Air Detonation Wave around Obstacles Using Detailed Reaction Models

To observe the break up and re-generation of the detonation cell structure, a 2-D computation of detonation propagating around a circular obstacle was conducted. FEFLO with detailed chemical reaction model was applied to this 2-D simulation. The various blockage ratios between the tube width and the obstacle diameter were tested to investigate the effect on the break up/re-generation of the detonation cell structure. In this study, the detonation wave propagation was highly affected when the blockage ratio became larger. The simulation captured the break up and re-generation of the detonation cell structure behind the obstacle.

Numerical Modeling of Multi-Phase, Multi-Material Blast- Structure Interactions

This paper describes results of a combined experimental and computational effort intended to validate predictions of a coupled CFD/CSD methodology of a multi-plate steel structure response to blast loading. To improve our understanding of the complex controlling physical mechanisms we formulated a simplified, multi-step approach. First, we investigated a precision test of a single event, the response of a single steel plate to a close-in bare charge. Next, we added a second plate to examine the response of the second plate to blast and flyer plate loading. Finally, we placed water-filled tube s under the first plate, to investigate the feasibility of using water tubes to disperse and di ssipate flyer-plate kinetic energy. The modeling of blast and structure (flyer plate) inter action with water required the development of a new numerical algorithm that combines flow solvers for both the gas and the liquid via an immersed body approach. Both solvers run concurrently. In the gas phase region (i.e. compressible flow), the velocities of the liquid were imposed wherever liquid is present. For the liquid region (incompressible (+VO F)), the pressures of the gas region were imposed wherever gas was present. This multiphase flow solver is then coupled to our structural mechanics solver to calculate structural response to blast and the feasibility of using fluid dampers. The results demonstrate that t he approach taken here is capable of efficiently modeling complex multiphase problems.

The simulation of dust effects from fragmenting charges

Purpose – The purpose of this paper is to determine the reason for the discrepancy in estimated and observed damage caused by fragmenting charges in closed environments. Design/methodology/approach – A series of carefully conducted physical and numerical experiments was conducted. The results were analyzed and compared. Findings – The analysis shows that for fragmenting charges in closed environments, dust plays a far larger role than previously thought, leading to much lower pressures and damage. Research limitations/implications – In light of these findings, many assumptions and results for fragmenting charges in closed environments need to be reconsidered. Practical implications – This implies that for a far larger class of problems than previously estimated it is imperative to take into consideration dust production and its effect on the resulting pressures. Originality/value – This is the first time such a finding has been reported in this context.

Numerical Simulation Modeling of Aluminum Burning for Heavily Aluminized HE

The objective of this investigation is to model the burning of aluminum particles. An aluminum evaporation/reaction model was incorporated within a multi-phase flow model. The new scheme was applied to the simulation of blast wave evolution, where the HE model includes a significant percentage of aluminum particles, whose long-time burning and energy release must be considered. The evaporation of small aluminum particles with diameters from 5 to 500micron, reacting with oxygen, water, and carbon dioxide was initially tested in a 1-D code. The pressure profiles were significantly different than those obtained an inert aluminum model and from a single-reaction model which only considered a reaction with oxygen. Once validated, the models from 1-D code were incorporated into a 3-D production code. The newly developed 3D flow that includes the aluminum burning model was compared with experimental data. Results with the new model showed very good agreement in terms of the blast evolution, pressure, impulse, and energy behind the wave.