1,720,976 research outputs found
On the application of congruent upwind discretizations for large eddy simulations
No full textUpwind schemes were judged inappropriate for performing accurate large eddy simulations of turbulent flow owing
to the artificial dissipation that is present at high wavenumbers of the energy content. Such a conclusion has been drawn
also from some results obtained by adopting Finite Difference schemes. The present paper illustrates the performances
of some new Finite Volume upwind discretization of the convective terms in the case of the 1-D Burgers model equation
while studying the effects of numerical discretization on several Sub-Grid Scales turbulence models, starting from the
classical static and dynamic eddy viscosity models through the recent deconvolution-based ones. Basing on previously
published papers, large eddy simulations along with a deconvolution-based procedure for de-filtering the evolving
variable, have been originally developed and applied. It will be shown how the coherent application of the procedure
allows us to develop high-order accurate Finite Volume upwind schemes, which maintain a good spectral resolution
in the entire range of resolved scale. Such schemes can be candidate for performing accurate simulations of real
turbulence
Using symbolic computation software packages in production of multidimensional finite volume-based large eddy simulation codes
No full textThe numerical simulation of turbulence is one of the most challenging tasks in the field of the modern computational science. At present, the most advanced approach is the large eddy simulation (LES) technique wherein a formal separation between resolved (large) and unresolved (small) scales of the motion is in effect by means of a filtering operation applied onto the governing equations. However, LES requires very sophisticated numerical discretizations in terms of both accuracy and efficiency. Often, the modelling of the unresolved subgrid scale terms adds further computational complexities. This paper illustrates the suitability in using software packages for symbolic computation (in the present case, Maple© for helping in the production of subroutines for a new multidimensional, high-order accurate finite volume-based LES code. Specifically, it will be detailed how producing, rapidly and efficiently, the routines for computing convective, diffusive as well as subgrid scale modelling fluxes. It is particularly detailed how exploiting the package for differential calculus and linear algebra for the analytical integration of the flux polynomials over the finite volume faces. The structure of the LES code is illustrated, and an accuracy analysis of the local truncation errors is performed comparing the third-order accurate multidimensional upwind and the classical second-order centred reconstruction in the wavenumbers space. Then, some numerical results for the turbulent plane channel and some brief points concerning the parallelization issue are addressed. Copyright © 2012 John Wiley & Sons, Ltd
On the control of the mass errors in Finite Volume-based approximate projection methods for large eddy simulations
No full textFiltering in Large Eddy Simulation (LES) is often only a formalism since practically discretization of both the domain and operators is used as implicit grid-filtering to the variables. In the present study, the LES equations are written in the integral form around a Finite Volume (FV) Ώ rather than in the differential form as is more usual in Finite Differences (FD) and Spectral Methods (SM). Grid-filtering is therefore associated to the use of an explicit local volume average, by the way of surface flux integrals, and specific LES equations are here described. Moreover, since the filtered pressure characterizes itself only as a Lagrange multiplier used to satisfy the continuity constraint, projection methods are used for obtaining a divergence-free velocity. The choice of the non-staggered collocation is often preferable since is easily extendable on general geometries. However, the price to be paid in the so-called Approximate Projection Methods, is that the discrete continuity equation is satisfied only up to the magnitude of the local truncation error. Thus, the effects of such source errors are analyzed in FD and FV-based LES of turbulent channel flow. It will be shown that the FV formulation is much more efficient than FD in controlling the errors
On the use of Aggregation-based Parallel Multilevel Preconditioners in the LES of Wall-bounded Turbulent Flows
No full textThis work is concerned with the application of algebraic multilevel preconditioners in the solution of pressure linear systems arising in the large eddy simulation of turbulent incompressible flows in wall-bounded domains. These systems, coming from the discretization of elliptic equations with periodic and Neumann boundary conditions, are large and sparse, singular, compatible, and nonsymmetric because of the use of non-uniform grids taking into account the anisotropy of the flow. Furthermore, they generally account for a large part of the simulation time. We analyse, through numerical experiments, the effectiveness of parallel algebraic multilevel Schwarz preconditioners, based on the smoothed aggregation technique, in the iterative solution of the above pressure systems. We also investigate the behaviour of a variant of the smoothed aggregation technique, recently developed to efficiently deal with nonsymmetric systems
Free topology generation of thermal protection system for reusable space vehicles using integral soft objects
No full textThe present paper deals with a modelling procedure developed to design the thermal protection system of a Reusable Space Vehicle. Clusters of Skeleton-based Integral Soft Objects are created to assign independent distributions of thickness according to an arbitrary boolean map which represents two different insulating materials. The procedure is morphologically independent, and allows a powerful and local control of thickness and material distribution. The effectiveness of the modelling procedure is shown with applications to Reusable Space Vehicle concepts
FREE TOPOLOGY GENERATION OF THERMAL PROTECTION SYSTEM FOR REUSABLE SPACE VEHICLES USING INTEGRAL SOFT OBJECTS, XXIV AIMETA 2019 XXIV CONFERENCE
No full textThe present paper deals with a modelling procedure developed to design the thermal protection system of a Reusable Space Vehicle. Clusters of Skeleton-based Integral Soft Objects are created to assign independent distributions of thickness according to an arbitrary boolean map which represents two different insulating materials. The procedure is morphologically independent, and allows a powerful and local control of thickness and material distribution. The effectiveness of the modelling procedure is shown with applications to Reusable Space Vehicle concepts
Low speed longitudinal aerodynamics of a blended wing-body re-entry vehicle
No full textThis paper deals with the evaluation of low-speed longitudinal aerodynamic performances of a vehicle concept with an unconventional blended wing-body aeroshape. The spacecraft is intended as a multipurpose vehicle for future International Space Station payload and/or crew servicing and support, able to perform a lifting re-entry from Low Earth Orbit and to land on a conventional runway. The aeroshape features a high-sweep near double delta-shaped configuration, equipped with two functionally independent body flaps, which can be used for both longitudinal control (i.e., elevon mode) and lateral-directional control (i.e., aileron mode). Longitudinal aerodynamic force and moment coefficients are investigated with Computational Fluid Dynamics simulations carried out at Mach number equal to 0.3, typical of landing conditions. A comparison of low-speed performances for clean and flapped configurations is performed considering several vehicle attitudes and elevon deflection angles. High-lift performances of the aeroshape are discussed and related to the onset conditions of vorticity field at various angles of attack. Additionally, comparison of aerodynamic coefficients with classical delta-wing theory is also discussed, addressing the promising capabilities of the selected design to perform a glided horizontal landing. Finally, a description of vortex break-down phenomena occurring on the aeroshape at landing incidence is discussed, accounting for the aerodynamic coefficients in post-stall condition, also providing an overall picture of the longitudinal static stability of the vehicle
Aerodynamic analysis of a supersonic transport aircraft at landing speed conditions
No full textSupersonic flight for commercial aviation is gaining a renewed interest, especially for business aviation, which demands the reduction of flight times for transcontinental routes. So far, the promise of civil supersonic flight has only been afforded by the Concorde and Tupolev T-144 aircraft. However, little or nothing can be found about the aerodynamics of these aeroshapes, the knowledge of which is extremely interesting to obtain before the development of the next-generation high-speed aircraft. Therefore, the present research effort aimed at filling in the lack of data on a Concorde-like aeroshape by focusing on evaluating the aerodynamics of a complete aircraft configuration under low-speed conditions, close to those of the approach and landing phase. In this framework, the present paper focuses on the CFD study of the longitudinal aerodynamics of a Concorde-like, tailless, delta-ogee wing seamlessly integrated onto a Sears–Haack body fuselage, suitable for civil transportation. The drag polar at a Mach number equal to 0.24 at a 30 m altitude was computed for a wide range of angles of attack (0◦, 60◦), with a steady RANS simulation to provide the feedback of the aerodynamic behaviour post breakdown, useful for a preliminary design. The vortex-lift contribution to the aerodynamic coefficients was accounted for in the longitudinal flight condition. The results were in agreement with the analytical theory of the delta-wing. Flowfield sensitivity to the angle of attack at near-stall and post-stall flight attitudes confirmed the literature results. Furthermore, the longitudinal static stability was addressed. The CFD simulation also evidenced a static instability condition arising for 15◦ ≤ α ≤ 20◦ due to vortex breakdown, which was accounted for
Aerodynamic optimization of airfoils shape for atmospheric flight on Mars planet
No full textFixed-wing aircraft are particularly attractive for Mars surface exploration, but Martian low-density atmosphere
poses several issues to airfoil aerodynamic design. In this framework, the paper deals with an optimization
procedure aimed at maximize the aerodynamic efficiency of Low-Reynolds airfoils. The design procedure
embeds airfoil parameterization, aerodynamic computation, and optimization algorithm for a maximum
efficiency objective at two Reynolds. Two airfoil parameterization models are developed
and adopted within the design optimization. The XFoil solver is considered to address airfoil aerodynamics;
while its optimal shape is generated with a genetic algorithm to simulate a cruising condition. Design
optimization developed two different airfoils with maximum lift-to-drag equal to 10.4 and 16.4.
Aerodynamic performances of these wing sections are discussed in the work. Optimal airfoils pointed out that
maximization of aerodynamic efficiency is associated to both a thickness reduction and a curvature increase
of the aeroshape. Finally, aerodynamics of the optimal airfoils are also investigated with computational fluid
dynamics simulations
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