Acquisto e godimento dell'abitazione familiare tra norme di favore e imposizione patrimoniale

L'articolo tratta del regime fiscale dell'acquisto e del possesso dell'abitazione familiare, illustrandone i caratteri e valutandone i diversi aspetti problematici

Hypersonic Aerothermochemistry Duplication in Ground Plasma Facilities: A Flight-to-Ground Approach

peer reviewedHigh conservative safety margins, applied to the design of spacecraft thermal protection systems for planetary entry, need to be reduced for higher efficiency of future space missions. Ground testing of such protection systems is of great importance during the design phase. This study covers a methodology for simulating the complex hypersonic entry aerothermochemistry in a plasma wind tunnel for a given spacecraft geometry without any assumption on axisymmetry or bluntness. A demonstration of this proposed methodology is made on the Qubesat for Aerothermodynamic Research and Measurements on AblatioN, QARMAN mission, which is a rectangular reentry CubeSat with a cork-based ablative thermal protection system in the front unit. The reacting boundary-layer profiles of the hypersonic entry probe compare well with the ones developing at the stagnation region of the plasma test model, defined with the proposed flight-to-ground duplication method

A gas-surface interaction model for the numerical study of rocket nozzle flows over pyrolyzing ablative materials

Ablative materials provide a widespread, reliable, and relatively low–cost way to manage the extremely high heat fluxes that are normally encountered in a wide variety of aerospace applications. Typically, both non–pyrolyzing carbon–based and pyrolyzing carbon– and silica–based materials are used with this intent in rocket nozzles. Unfortunately, during the rocket firing these materials undergo a consumption that modifies the nozzle internal contour increasing the nozzle throat area and causing a drop down of the chamber pressure that, ultimately, results in an overall rocket performance reduction. For this reason, it is important to advance the fundamental understanding of the nozzle erosion processes and to develop useful scientific tools in this subject area. To this aim, a comprehensive model that would allow the study of the behavior of different ablative materials in rocket nozzle environment accounting for surface ablation, pyrolysis gas in- jection and resin decomposition has been developed, tested and validated. The model relies on surface mass and energy balances and deals with the gas–surface interaction erosive phenomena, accurately solving the gas side, using a CFD ap- proach. Two different ablation models have been implemented to simulate both the erosion of carbon– and silica–based materials. The steady–state ablation approximation is used in order to estimate the solid conductive heat flux, as well as the pyrolysis gas mass flow rate, in a closed way and without requiring the accurate resolution of the material heating by means of a thermal response code. Firstly, the talk will address a thorough description of the theoretical/numerical model. Then, several simulations, from sub–scale to full–scale nozzles, will be presented and the results will be compared with the experimental results

A gas-surface interaction model for the numerical study of rocket nozzle flows over pyrolyzing ablative materials

Ablative materials provide a widespread, reliable, and relatively low–cost way to manage the extremely high heat fluxes that are normally encountered in a wide variety of aerospace applications. Typically, both non–pyrolyzing carbon–based and pyrolyzing carbon– and silica–based materials are used with this intent in rocket nozzles. Unfortunately, during the rocket firing these materials undergo a consumption that modifies the nozzle internal contour increasing the nozzle throat area and causing a drop down of the chamber pressure that, ultimately, results in an overall rocket performance reduction. For this reason, it is important to advance the fundamental understanding of the nozzle erosion processes and to develop useful scientific tools in this subject area. To this aim, a comprehensive model that would allow the study of the behavior of different ablative materials in rocket nozzle environment accounting for surface ablation, pyrolysis gas in- jection and resin decomposition has been developed, tested and validated. The model relies on surface mass and energy balances and deals with the gas–surface interaction erosive phenomena, accurately solving the gas side, using a CFD ap- proach. Two different ablation models have been implemented to simulate both the erosion of carbon– and silica–based materials. The steady–state ablation approximation is used in order to estimate the solid conductive heat flux, as well as the pyrolysis gas mass flow rate, in a closed way and without requiring the accurate resolution of the material heating by means of a thermal response code. Firstly, the talk will address a thorough description of the theoretical/numerical model. Then, several simulations, from sub–scale to full–scale nozzles, will be presented and the results will be compared with the experimental results

CFD Ablation Predictions with Coupled GSI Modeling for Charring and non-Charring Materials

To this day, a major objective of TPS design is to reduce empiricism, and to increase fundamental modeling capability through increased understanding. One of the most challenging aspect is the proper coupling between the material response and the external flow field. With this regard, the goal of this research activity is the improvement of the numerical modeling capabilities through the development of advanced CFD tools integrated with Gas-Surface Interaction (GSI) modeling. Numerical prediction of ablation is ambitious and cpu-time demanding due to the complex multiphase physical and chemical processes that occur. With improvements in computational algorithms and advances in computer hardware, Navier- Stokes based approaches have become the norm in recent years for coupling to material thermal response predictions. The present state of the art in fluid-material coupling is represented by loose coupling of a high-fidelity CFD flow solver with a material thermal response code. In that respect, some major restrictions are still present in these state of the art coupled solutions: surface chemical equilibrium assumption non-ablating flow field prediction simplified diffusion modeling based on transfer coefficient Chemical equilibrium is a special condition of the general chemical nonequilibrium condition and surface recession rate predicted by the chemical equilibrium surface chemistry is usually reasonably conservative and is considered to be a best alternative when the nonequilibrium computation is too expensive or unlikely to be achieved. The ablation models are currently largely based on the surface equilibrium assumption and the effects and importance of non-equilibrium ablation models coupled with CFD tools are only beginning to be explored. Moreover, the coupling between CFD solver and material response code is often made considering non-ablating flow field solutions assuming a fully/super-catalytic, radiative equilibrium wall. This means that the effect on the flow field solution of the ablation and pyrolysis gas injection and of variable surface temperature are treated only approximately relying on the use of mass and energy transfer coefficients and semi-empirical blowing correction equations. Finally, the ablation rate is generally computed by the material response code using thermochemical tables and extremely simplified diffusion models based on transfer coefficients and semi-empirical relations relating mass and energy transfer. The objective of this research activity is to remove these major limiting assumptions developing suitable finite-rate GSI models and integrating CFD technology with Computational Surface Thermochemistry (CST) to take into account the effect of surface ablation and pyrolysis gas injection on the flow field and to allow surface ablation and surface temperature distributions to be determined as part of the CFD solution. Because the entire flow field is to be solved with ablative boundary conditions, the film-transfer theory assumption is no longer needed; this will permit to avoid all of the classical approximations such as transfer coefficients, equilibrium thermochemical tables, and blowing correction equations which needs to be used when ablative boundary conditions are not accounted for in the CFD solution. The ablative boundary conditions, based on finite-rate chemistry, species mass conservation and surface energy balance, is discretized and integrated with the CFD code to predict aerothermal heating, surface temperature, gas-phase surface composition, and surface ablation rate. The concentrations of chemical species at wall are determined from finite-rate gas-surface chemical reactions balanced by mass transfer rate. The surface temperature is determined from the surface energy balance assuming steady-state ablation or coupling with a thermal response code. The surface recession rate and the surface temperature are thus obtained as part of the flow field solution. The computational tool developed in this work is used to simulate two sets of experimental data for nozzle material ablation: sub-scale motor tests carried out for the Space Shuttle Reusable Solid Rocket Motor and the static firing tests of the second and third stage solid rocket motors of the European VEGA launcher which use carbon-carbon for the throat insert and carbon-phenolic for the region downstream of the throat

Uncertainty Analysis of Carbon Ablation in the VKI Plasmatron

International audienc

Affected depth and effective reactivity in porous thermal protection materials for atmospheric re-entry

International audienceAffected depth and effective reactivity in porous thermal protection materials for atmospheric re-entr

Detailed Modeling of Cork-Phenolic Ablators in Preparation for the Post-flight Analysis of the QARMAN Re-entry CubeSat

This work deals with the analysis of the cork P50, an ablative thermal protection material (TPM) used for the heat shield of the qarman Re-entry CubeSat. Developed for the European Space Agency (ESA) at the von Karman Institute (VKI) for Fluid Dynamics, qarman is a scientifc demonstrator for Aerothermodynamic Research. The ability to model and predict the atypical behavior of the new cork-based materials is considered a critical research topic. Therefore, this work is motivated by the need to develop a numerical model able to respond to this demand, in preparation to the post-fight analysis of qarman. This study is focused on the main thermal response phenomena of the cork P50: pyrolysis and swelling. Pyrolysis was analyzed by means of the multi-physics Computational Fluid Dynamics (CFD) code argo, developed at Cenaero. Based on a unifed fow-material solver, the Volume Averaged Navier–Stokes (VANS) equations were numerically solved to describe the interaction between a multi-species high enthalpy fow and a reactive porous medium, by means of a high-order Discontinuous Galerkin Method (DGM). Specifcally, an accurate method to compute the pyrolysis production rate was implemented. The modeling of swelling was the most ambitious task, requiring the development of a physical model accounting for this phenomenon, for the purpose of a future implementation within argo. A 1D model was proposed, mainly based on an a priori assumption on the swelling velocity and the resolution of a nonlinear advection equation, by means of a Finite Diference Method (FDM). Once developed, the model was successfully tested through a matlab code, showing that the approach is promising and thus opening the way to further developments

Migratory restlessness in shorebirds (Aves, Charadriiformes). A case study by means of accelerometers

The knowledge of individual and environmental parameters affecting stopover length in shorebirds is important for the conservation and management of species and habitats often seriously threatened, such as Mediterranean wetlands. The role of external factors affecting the decision to leave a stopover site is not always easy to study in the field, due to the high number of variables (i.e., atmospheric conditions) potentially involved. Combining both field and laboratory research has proved to be extremely useful in order to identify the main factors affecting stopover length, at least in passerines. Recent studies demonstrated that the amount of migratory restlessness in these species can be considered a good proxy for quantifying the willingness to depart from a refuelling site. Even if shorebirds have proved to be good models for laboratory research, the only papers regarding migratory restlessness in this group concern studies on orientation mechanisms, which are mainly aimed at showing their use of magnetic compass. The present work aims at studying the migratory restlessness in shorebirds and its relation with body conditions and stopover length by using spring migrating Wood sandpiper (Tringa glareola) as a model species. Despite this method proved to be effective in recording Wood sandpipers activity, we failed to found any relationship among their stopover length, body conditions and nocturnal activity. The degree of nocturnal activity was overall low, whereas a peak in activity was registered at sunset. This twilight activity was oriented, and its amount varied significantly according to the amount of available food in captivity. Our results suggested that migratory restlessness in shorebirds might show some peculiar characteristics that would deserve further investigations