摘要:

We investigate the practicability of an optimization algorithm based on the Broyden-Fletcher-Goldfarb-Shanno (BFGS) method for 3D shape design problems, using approximate sensitivities of objective functions, where the contribution of the partial derivatives of the flow state with respect to the control variables is neglected. Therefore, it is worthwhile to investigate how an optimization method based on the Hessian behaves in this context. Indeed, the Hessian should be far from its real value if the gradient approximation is wrong. The optimization methodology is characterized by an unstructured CAD-free framework for shape and mesh deformations, an automatic differentiation of programs for the computation of the gradient of the cost function, and an unstructured flow solver. The redesign of transonic and supersonic wings has been considered and the performance of the BFGS method has been analyzed in comparison with a steepest descent method. Taking into account that a line search is too expensive to be carried out in such problems, a step size proportional to the gradient modulus has been employed for updating the control variables. Numerical results show that the BFGS method does not suffer from the approximation used in the evaluation of sensitivities, and leads to an effective improvement of the efficiency of the optimization methodology. These results can be then considered an aposteriorijustification for incomplete sensitivities.

ISSN:1061-8562    

DOI:10.1080/10618560008940718

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The main objective of this paper is to provide some adequate way to compute the non-conservative hyperbolic system which describes a multicomponent turbulent flow. The model is written for an isentropic gas. The exact solution of the Riemann Problem (RP) associated to the hyperbolic system is exhibited. It is composed of constant states separated by rarefaction waves, or shock waves and a contact discontinuity.

ISSN:1061-8562    

DOI:10.1080/10618560008940719

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A fast, matrix-free implicit method has been developed to solve low Mach number flow problems on unstructured grids. The preconditioned compressible Euler and Navier-Stokes equations are integrated in time using a linearized implicit scheme. A newly developed fast, matrix-free implicit method, GMRES + LU−SGS, is then applied to solve the resultant system of linear equations. A variety of computations has been made for a wide range of flow conditions, for both in viscid and viscous flows, in both 2D and 3D to validate the developed method and to evaluate the effectiveness of the GMRES + LU−SGS method. The numerical results obtained indicate that the use of the GMRES + LU−SGS method leads to a significant increase in performance over the LU−SGS method, while maintaining memory requirements similar to its explicit counterpart. An overall speedup factor from one to more than two order of magnitude for all test cases in comparison with the explicit method is demonstrated.

ISSN:1061-8562    

DOI:10.1080/10618560008940720

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper some results based on the near-wall mean characteristics of a bounded turbulent flow are presented. In the study empirical polynomials and experimental data for an attached wall-bounded flow are used with the objective of studying the time-scales similarities in the very-near-wall region. As a result of this analysis a new parameter to characterize the high to low-Reynolds turbulence transition in the context of turbulence models is proposed. A relation for the Reynolds stress in the buffer region is also proposed, which allows a mean velocity profile through the buffer region to be obtained. This mean velocity profile joins the logarithmic ones at the beginning of the inertial sub-layer and fits appropriately to experimental data. Another result derived from the previous analysis is an expression for the eddy viscosity through the very-near-wall region. Comparison of this expression with those relations used by four known low-Reynolds models reveals that it has a very good performance.

ISSN:1061-8562    

DOI:10.1080/10618560008940721

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this paper we have investigated free-surface unsteady viscous flow through porous media using a finite difference technique via primitive formulation. A transformation has been used to convert the irregular flow domain into a rectangular domain. Two illustrations have been presented in case of a standing wave problem and a cavity flow problem with a free surface. The method is found satisfactory for numerical solution for Reynolds number upto 200.

ISSN:1061-8562    

DOI:10.1080/10618560008940722

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor