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Cozzolino D.,University of Naples Federico II | Parrilli S.,Centro Italiano Ricerche Aerospaziali | Scarpa G.,University of Naples Federico II | Poggi G.,University of Naples Federico II | Verdoliva L.,University of Naples Federico II
IEEE Geoscience and Remote Sensing Letters | Year: 2014

Despeckling techniques based on the nonlocal approach provide an excellent performance, but exhibit also a remarkable complexity, unsuited to time-critical applications. In this letter, we propose a fast nonlocal despeckling filter. Starting from the recent SAR-BM3D algorithm, we propose to use a variable-size search area driven by the activity level of each patch, and a probabilistic early termination approach that exploits speckle statistics in order to speed up block matching. Finally, the use of look-up tables helps in further reducing the processing costs. The technique proposed conjugates excellent performance and low complexity, as demonstrated on both simulated and real-world SAR images and on a dedicated SAR despeckling benchmark. © 2013 IEEE.


Marongiu C.,Centro Italiano Ricerche Aerospaziali | Tognaccini R.,University of Naples Federico II
AIAA Journal | Year: 2010

A new far-field method is proposed for the analysis of the aerodynamic force acting on an airfoil in subsonic unsteady flow conditions given a numerical solution of the flowfield. For this purpose, a recent theory proposed by Wu et al. (Wu, J.-Z., Ma, H.-Y., and Zhou, M.-D., Vorticity and Vortex Dynamics, Springer, New York, 2006), relating the aerodynamic force acting on a body to the Lamb vector (the cross product of the vorticity by the velocity) in case of unsteady Navier-Stokes flow, has been extended to the analysis of high-Reynolds-number turbulent flows governed by the Reynolds-averaged Navier-Stokes equations. The applications showed here concern the analysis of numerical solutions around an airfoil in steady flow and in pitching oscillations including a dynamic-stall condition. Both lift and drag coefficients have been computed by means of Lamb vector integrals and have been compared with the reference near-field results (stress integration on the body). The method allows for the decomposition of the aerodynamic force in a contribution associated with the bound vorticity on the body and a contribution related to the free vorticity developing in the airfoil wake. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


Viviani A.,The Second University of Naples | Pezzella G.,Centro Italiano Ricerche Aerospaziali | Pezzella G.,Research Engineer
Journal of Spacecraft and Rockets | Year: 2010

This paper deals with aerodynamic and aerothermodynamic studies carried out to design a capsule vehicle suitable for the recovery of crew members from the International Space Station and/or from exploration missions to the moon or Mars. An integrated design tool called ENTRY is used to support vehicle reentry analysis and computational fluid dynamics design activities. A possible low-Earth-orbit reentry scenario, with the associated aeroheating environment, is generated and then analyzed. Several Euler and Navier-Stokes computations are performed to simulate the flowfleld past the vehicle, for both perfect-gas and nonequilibrium reacting-gas models for the air. Numerical results and their comparison with flight data and wind-tunnel data are presented. An analysis of flowflelds, obtained from numerical computations, is provided by means of flight forces and moments coefficients. Experimentally measured surface pressure distributions and aerodynamic coefficients compare rather well with numerical results.


Casalino D.,Centro Italiano Ricerche Aerospaziali | Casalino D.,Aerodynamics and Aeroacoustics Laboratory | Barbarino M.,Centro Italiano Ricerche Aerospaziali | Barbarino M.,Aerodynamics and Aeroacoustics Laboratory
AIAA Journal | Year: 2011

A stochastic Fourier method for the computation of synthetic solenoidal velocity fluctuations from a steady Reynolds-averaged Navier-Stokes solution is revised, validated against jet-noise experimental data, and applied to the problem of noise radiation from the trailing edge of a NACA-0012 airfoil. The method is used to compute the source term of the Howe's acoustic analogy equation for an isentropic flow that is solved in the frequency domain using a finite element discretization. For each spectral component of the source term, a prescribed number of realizations of the synthetic source field is generated by seeding the random number generator. The corresponding sound fields are then computed and finally averaged to track statistically converged noise spectra. The self-noise spectra computed for an airfoil at different values of the freestream velocity are compared with literature experimental data and semianalytical predictions. It is shown that the finite element results are in fairly good agreement with both the semianalytical results and the measurements. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


Capizzano F.,Centro Italiano Ricerche Aerospaziali
AIAA Journal | Year: 2016

Immersed boundary methods showed a good compliance for a wide range of complex inviscid and viscous flows. Moreover, the high-Reynolds-number regime still remains an open issue. The paper describes a wall-layer approach to answer the need of a model that goes beyond the actual capability of classical wall functions. A near-wall region is established that gets information from the outer flowfield and returns back the wall stress. The latter is obtained by integrating simplified thin-boundary-layer equations along a normal to the wall subgrid. In the outer zone, the compressible Reynolds-averaged Navier-Stokes equations are solved by means of a finite volume method on two-or three-dimensional Cartesian meshes. The classic validation test dealing with a high-Reynolds-number flow over a flat plate is carried out. A benchmark two-dimensional complex flow is numerically investigated to assess the performance of the wall model in case of a pressure-induced separation. The results are compared with both experiments and body-conforming numerical solutions. © Copyright 2015 by the authors.


Carozza A.,Centro Italiano Ricerche Aerospaziali
Applied Thermal Engineering | Year: 2016

This paper deals with the numerical analysis of the effect a heat exchanger has on the flow field in an oil cooling system for aerospace applications. To this end, an important upgrade of the UZEN in house CIRA Reynolds Averaged Navier-Stokes solver has been carried out to account for the pressure drop and heat rejection that usually are present in a heat exchanger. This upgrade is based on the addition of a source term in the momentum and energy equations of balance, respectively, whose values are updated during the simulation. The correspondent code modification needs a proper validation before any concrete application. At this aim, a two dimensional channel has been firstly studied in order to test the accuracy of the UZEN code. Then a three dimensional circular duct has been studied with a porous insert to validate the porous approach robustness. After this preliminary campaign of assessment, a new generation two engine aircraft has been studied with particular emphasis on its nacelle cooling system. Velocity and pressure are compared using different turbulence models with the well known Fluent ones. The more interesting parameter for such an investigation is the mass flow rate through the cooling ducts as computed by UZEN that show a good agreement with the Fluent one. © 2016 Elsevier Ltd. All rights reserved.


Bucchignani E.,Centro Italiano Ricerche Aerospaziali | Pezzella G.,Centro Italiano Ricerche Aerospaziali
Mathematics and Computers in Simulation | Year: 2010

A mathematical model able to deal with high temperature gas effects in hypersonic flow fields is presented. In order to assess this model, four typical hypersonic applications are considered. The numerical results are presented and compared with experimental data. The effects of the catalyticity of the materials on the heat fluxes are also highlighted. © 2010 IMACS.


Capizzano F.,Centro Italiano Ricerche Aerospaziali
AIAA Journal | Year: 2011

This paper describes the development of a wall model to extend the applicability of immersed boundary methods to high-Reynolds-number flows. A two-layer approach, based on a decomposition of the near-wall region, is adopted. An outer region is governed by the compressible Reynolds-averaged Navier-Stokes equations, which are solved numerically by using a classical finite volume method. In the proximity of the wall, an inner zone is established and modeled by a simplified version of the thin-boundary-layer equations. The simulation platform is based on Cartesian meshes and an immersed boundary technique. It is able to solve the steady Euler/Reynolds-averaged Navier-Stokes equations in two-and three-dimensional coordinates. The robustness and the accuracy of the methodology are discussed. At present, this work represents the last advance of a research activity for which the final goal is a fast predesign tool for aeronautical/industrial applications. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.


Carozza A.,Centro Italiano Ricerche Aerospaziali
46th AIAA Thermophysics Conference | Year: 2016

The purpose of this paper is to show the results of the application of the CHT method to an aeronautical configuration of interest. To perform these analyses the three heat transfer mechanisms, conduction, radiation and convection, were considered joining the solutions of the solid and fluid regions at the interface. Numerically, the two domains are treated separately in a first moment and then, at the end of each iteration, they are coupled by imposing the equivalence of the gradients. Conductive walls where the Fourier heat flux is considered only in direction normal to the wall, are used. The fluid domain is studied, instead, by a finite volume, implicit and second order accurate code. After a preliminary study carried out on a 2D square cavity, a new generation turboprop nacelle built with three different metallic materials has been taken into consideration. Particular attention has been paid to the thermal fields and the heat exchange rates achieved on the skin both in cruise (T∞=253 ̶ 273 K; P∞=72500 Pa) and in idle (T∞=273 ̶ 293 K; P∞=101325 Pa). The results show how the CHT approach in the aerodynamic investigations can affect the aerodynamic predictions in not negligible manner. Indeed, the thermal conductivity plays a relevant role on the internal convective and radiative heat transfer on the single walls. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All right reserved.


Casalino D.,Centro Italiano Ricerche Aerospaziali
AIAA Journal | Year: 2012

A weak discretizationinthe frequency domainofthe Lilley-Goldstein acoustic analogy equationispresented. This equation is cast into a linear system of two equations that are successively arranged in a convenient form for a Galerkin projection. The method is applied to compute the sound generated by Dirac ring sources of different azimuthal order and radius and propagated through an axisymmetric parallel jet. The effects due to the jet temperature and velocity profile combined with the effects due to the source frequency, radius, and azimuthal order are illustrated through extensive parametric results. It is shown that three-dimensional Green's functions can be reconstructed by superposition of few axisymmetric solutions of low azimuthal order when the sources are located inside the jet. Finally, tones from annular sources locatedinthe potential core of amixing jet are propagated through the jet shear layer and compared with the tones computed in uniform flow conditions. It is shown that, for conditions that are representative of a propeller rig located in the potential core of a wind-tunnel jet, the shear-layer refraction effects can be corrected by using a thin-layer approximation. Copyright © 2011.

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