Examinando por Autor "Ponsin, J."

Mostrando 1 - 5 de 5

Restringido
Analytic adjoint solutions for the 2-D incompressible Euler equations using the Green's function approach
(Cambridge University Press, 2022-06-13) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
The Green's function approach of Giles and Pierce (J. Fluid Mech., vol. 426, 2001, pp. 327–345) is used to build the lift and drag based analytic adjoint solutions for the two-dimensional incompressible Euler equations around irrotational base flows. The drag-based adjoint solution turns out to have a very simple closed form in terms of the flow variables and is smooth throughout the flow domain, while the lift-based solution is singular at rear stagnation points and sharp trailing edges owing to the Kutta condition. This singularity is propagated to the whole dividing streamline (which includes the incoming stagnation streamline and the wall) upstream of the rear singularity (trailing edge or rear stagnation point) by the sensitivity of the Kutta condition to changes in the stagnation pressure.
Restringido
Exact inviscid drag-adjoint solution for subcritical flows
(Aerospace Research Central, 2021-09-25) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
Restringido
Explaining the lack of mesh convergence of inviscid adjoint solutions near solid walls for subcritical flows
(Multidisciplinary Digital Publishing Institute (MDPI), 2023-04-24) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
Numerical solutions to the adjoint Euler equations have been found to diverge with mesh refinement near walls for a variety of flow conditions and geometry configurations. The issue is reviewed, and an explanation is provided by comparing a numerical incompressible adjoint solution with an analytic adjoint solution, showing that the anomaly observed in numerical computations is caused by a divergence of the analytic solution at the wall. The singularity causing this divergence is of the same type as the well-known singularity along the incoming stagnation streamline, and both originate at the adjoint singularity at the trailing edge. The argument is extended to cover the fully compressible case, in subcritical flow conditions, by presenting an analytic solution that follows the same structure as the incompressible one.
Acceso Abierto
Shock equations and jump conditions for the 2D adjoint euler equations
(Multidisciplinary Digital Publishing Institute (MDPI), 2023-03-10) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
This paper considers the formulation of the adjoint problem in two dimensions when there are shocks in the flow solution. For typical cost functions, the adjoint variables are continuous at shocks, wherein they have to obey an internal boundary condition, but their derivatives may be discontinuous. The derivation of the adjoint shock equations is reviewed and detailed predictions for the behavior of the gradients of the adjoint variables at shocks are obtained as jump conditions for the normal adjoint gradients in terms of the tangent gradients. Several numerical computations on a very fine mesh are used to illustrate the behavior of numerical adjoint solutions at shocks.
Restringido
Singularity and mesh divergence of inviscid adjoint solutions at solid walls
(Elsevier, 2023-09-15) Lozano, Carlos; Ponsin, J.; Instituto Nacional de Técnica Aeroespacial (INTA)
The mesh divergence problem occurring at subsonic and transonic speeds with the adjoint Euler equations is reviewed. By examining a recently derived analytic adjoint solution, it is shown that the explanation is that the adjoint solution is singular at the wall. The wall singularity is caused by the adjoint singularity at the trailing edge, but not in the way it was previously conjectured.