Persona: Lozano, Carlos
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Instituto Nacional de Técnica Aeroespacial
El Instituto Nacional de Técnica Aeroespacial es el Organismo Público de Investigación (OPI) dependiente del Ministerio de Defensa. Además de realizar actividades de investigación científica y de desarrollo de sistemas y prototipos en su ámbito de conocimiento, presta servicios tecnológicos a empresas, universidades e instituciones.
El INTA está especializado en la investigación y el desarrollo tecnológico, de carácter dual, en los ámbitos de la Aeronáutica, Espacio, Hidrodinámica, Seguridad y Defensa.
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Lozano
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Carlos
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Publicación Restringido Entropy and adjoint methods(Springer Link, 2019-11-11) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)Aerodynamic drag can be partially approximated by the entropy flux across fluid domain boundaries with a formula due to Oswatitsch. In this paper, we build the adjoint solution that corresponds to this representation of the drag and investigate its relation to the entropy variables, which are linked to the integrated residual of the entropy transport equation. For inviscid isentropic flows, the resulting adjoint variables are identical to the entropy variables, an observation originally due to Fidkowski and Roe, while for non-isentropic flows there is a significant difference that is explicitly demonstrated with analytic solutions in the shocked quasi-1D case. Both approaches are also investigated for viscous and inviscid flows in two and three dimensions, where the adjoint equations and boundary conditions are derived. The application of both approaches to mesh adaptation is investigated, with especial emphasis on inviscid flows with shocks.Publicación Restringido Entropy production by implicit Runge–Kutta schemes(Springer Link, 2019-01-23) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)This paper follows up on the author’s recent paper “Entropy Production by Explicit Runge–Kutta schemes” (Lozano in J Sci Comput 76(1):521–564, 2018. https://doi.org/10.1007/s10915-017-0627-0), where a formula for the production of entropy by fully discrete schemes with explicit Runge–Kutta time integrators was presented. In this paper, the focus is on implicit Runge–Kutta schemes, for which the fully discrete numerical entropy evolution scheme is derived and tested.Publicación Restringido Watch your adjoints! Lack of mesh convergence in inviscid adjoint solutions(Aerospace Research Central, 2019-08-05) Lozano, Carlos; Instituto Nacional de Técnica Aeroespacial (INTA)It has been long known that 2D and 3D inviscid adjoint solutions are generically singular at sharp trailing edges. In this paper, a concurrent effect is described by which wall boundary values of 2D and 3D inviscid continuous and discrete adjoint solutions based on lift and drag are strongly mesh dependent and do not converge as the mesh is refined. Various numerical tests are performed to characterize the problem. Lift-based adjoint solutions are found to be affected for any flow condition, whereas drag-based adjoint solutions are affected for transonic lifting flows. A (laminar) viscous case is examined as well, but no comparable behavior is found, which suggests that the issue is exclusive to inviscid flows. It is argued that this behavior is caused by the trailing edge adjoint singularity.Publicación Acceso Abierto 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 Roca, Jorge; 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.Publicación Acceso Abierto On the Characteristic Structure of the Adjoint Euler Equations and the Analytic Adjoint Solution of Supersonic Inviscid Flows(Multidisciplinary Digital Publishing Institute (MDPI), 2025-05-30) Lozano, Carlos; Ponsin Roca, Jorge; Instituto Nacional de Técnica Aeroespacial (INTA)The characteristic structure of the two-dimensional adjoint Euler equations is examined. The behavior is similar to that of the original Euler equations, but with the information traveling in the opposite direction. The compatibility conditions obeyed by the adjoint variables along characteristic lines are derived. It is also shown that adjoint variables can have discontinuities across characteristics, and the corresponding jump conditions are obtained. It is shown how this information can be used to obtain exact predictions for the adjoint variables, particularly for supersonic flows. The approach is illustrated by the analysis of supersonic flow past a double-wedge airfoil, for which an analytic adjoint solution is obtained in the near-wall region. The solution is zero downstream of the airfoil and piecewise constant around it except across the expansion fan, where the adjoint variables change smoothly while remaining constant along each Mach wave within the fan.Publicación Acceso Abierto Shock equations and jump conditions for the 2D adjoint euler equations(Multidisciplinary Digital Publishing Institute (MDPI), 2023-03-10) Lozano, Carlos; Ponsin Roca, Jorge; 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.Publicación 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 Roca, Jorge; 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.Publicación Restringido Wall boundary conditions for lattice Boltzmann simulations of turbulent flows with wall functions(AIP Publishing, 2025-09-02) Ponsin Roca, Jorge; Lozano, CarlosThis paper investigates wall boundary condition schemes for the simulation of turbulent flows using the lattice Boltzmann method (LBM) coupled to turbulence models with wall functions. The analysis focuses on two schemes: a regularized boundary scheme with third-order reconstruction of the velocity gradients using wall function data and a slip-velocity bounce-back scheme. The LBM solver is coupled to the Spalart–Allmaras turbulence model and uses a model consistent wall function. The performance of the wall boundary schemes is assessed in two canonical turbulent flow cases, a fully developed channel flow and a zero-pressure-gradient flat plate boundary layer, selected specifically to isolate and analyze the impact of wall boundary treatments on turbulence modeling. The analysis shows that, for the selected test cases, the slip-velocity bounce-back approach, which has received relatively little attention within the context of LBM coupled to Reynolds-averaged Navier–Stokes turbulence models with wall functions, behaves fairly consistently in terms of both accuracy and mesh convergence. The regularized-based approach, on the other hand, appears to be highly sensitive to the reconstruction of the wall-normal velocity gradient, even in simple geometries, such as flat walls, where no interpolation is required. This dependency of the regularized boundary schemes on near-wall gradients, which had been noted before in the literature, requires the use of ad hoc gradient reconstruction techniques, requirements that are not present in the slip-velocity bounce-back method. A hybrid regularized boundary scheme that blends two different gradient reconstruction techniques but requires calibration is introduced as a tool to investigate this effect.Publicación Restringido Singularity and mesh divergence of inviscid adjoint solutions at solid walls(Elsevier, 2023-09-15) Lozano, Carlos; Ponsin Roca, Jorge; 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.Publicación Restringido Exact inviscid drag-adjoint solution for subcritical flows(Aerospace Research Central, 2021-09-25) Lozano, Carlos; Ponsin Roca, Jorge; Instituto Nacional de Técnica Aeroespacial (INTA)
