Papers by Alessandro Turchi
11th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, 2014
ABSTRACT Ablative materials are extensively used in several aerospace applications. Their employ ... more ABSTRACT Ablative materials are extensively used in several aerospace applications. Their employ as heat shield for re-entry capsules enables to survive re-entry conditions that would be otherwise unfeasible. The coupled experimental-numerical work is fundamental to grow the understanding of their behavior in operative conditions. This work deals with the develop- ment and testing of an ablation model able to reproduce the stagnation-point gas-surface interaction over non-charring carbon-based ablative materials. Numerical tools, specifi- cally developed at the von Karman Institute for Fluid Dynamics for re-entry application studies, are used together in the analysis to obtain relevant quantities as the stagnation- point surface mass blowing rate and temperature. Data from the experiments performed in the von Karman Institute Plasmatron in both air and nitrogen environment are used to compare with the numerical results and to tailor the ablation model. Test results in nitrogen environment prove that active surface nitridation takes place, and a proper nitri- dation reaction probability is extracted from the tests using the developed model with a reverse approach. Comparisons with the measured surface temperatures suggest that ad- ditional surface phenomena can occur in the low cold-wall heat flux tests. Surface nitrogen recombination, identified as one of these possible mechanisms, is analyzed.
Journal of Spacecraft and Rockets, 2015
A validated theoretical/numerical approach for the study of the erosion of graphite material has ... more A validated theoretical/numerical approach for the study of the erosion of graphite material has been used to parametrically analyze solid rocket motor thermal protections. The parametric numerical study of nozzle erosion has been carried out considering the role of propellant composition and nozzle geometry at first. Then the erosion rate dependence on chamber equilibrium conditions has been analyzed, showing that erosion rate increases with a nearly linear dependence with chamber pressure, whereas it is only marginally affected by chamber equilibrium composition and flame temperature variation with pressure. Finally, the effect of nozzle scale and entrance length has been also investigated permitting to quantify the erosion rate reduction caused by boundary layer thickening.
45th AIAA Thermophysics Conference, 2015
11th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, 2014
Ablation experiments have been carried out with the carbon-phenolic material AQ61 and a non-pyrol... more Ablation experiments have been carried out with the carbon-phenolic material AQ61 and a non-pyrolyzing carbon fiber preform in sub-and supersonic air and nitrogen plasmas in the VKI Plasmatron facility. We performed an in-situ recession analysis, including volumetric ablation, and observed the temperature and radiance of the surface for emissivity estimations, as well as spatial molecular radiation profiles in the boundary layer, which were compared to a numerical approach. Surface temperatures as low as 1600 K allowed observation of the temperature distribution over the surface using an infrared camera. The carbon preform test samples were varied in shape as well as regarding their fiber direction. Sublimation of the surface was reached in supersonic plasma flow at a cold wall heat flux of 9.5 MW/m 2 . Carbon preform emissivities were found to be in the order of 0.86 -0.97. A stagnation line description with an ablation boundary condition helped to reproduce experimentally measured boundary layer emission profiles of the CN violet molecule. In spite of the very simplified model, emission intensities were in the same order of magnitude compared to the experimental data. The model was able to reconstruct the location of the maximum emission for two cases. The char layer was examined by Scanning Electron Microscopy, illustrating degradation after nitrogen ablation.
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2013
48th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2012
47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 2011
ABSTRACT In the present study, modified surface mass and energy balances have been implemented in... more ABSTRACT In the present study, modified surface mass and energy balances have been implemented in the ablative boundary condition of a two-dimensional full Navier-Stokes solver, to take into account the pyrolysis gas injection. A finite- rate ablation model is used, with steady-state ablation approximation to obtain the surface temperature. Hence, with this approximation, the conductive heat flux entering the wall can be directly computed without coupling with a solid conduction solver. Moreover, under this approximation, the pyrolysis gas mass flow rate is a known fraction of the char mass flow rate. Simulations of carbon-phenolic solid rocket motor nozzle have been performed to validate the model and to investigate the most uncertain parameters. Results show the influence of pyrolysis gas composition and ratio between mass fluxes of pyrolysis gas and of gaseous carbon, over the final erosion.
43rd AIAA Thermophysics Conference, 2012
Journal of Propulsion and Power, 2014
ABSTRACT Surface roughness and radiation effects on the erosion behavior of a graphite nozzle are... more ABSTRACT Surface roughness and radiation effects on the erosion behavior of a graphite nozzle are studied for both metallized and nonmetallized propellants. A validated numerical approach that relies on a full Navier–Stokes flow solver coupled with a thermochemical ablation model is used for the analysis. A modification of the Spalart–Allmaras turbulence model is implemented to account for surface roughness. Net radiative heat flux is considered in the surface energy balance at the nozzle interface. Two different simplified models are used to evaluate the integral emissivity of dispersed alumina particles. Individual and combined effects of roughness and radiation are analyzed. Surface roughness enhances the erosion rate for both metallized and nonmetallized propellants noticeably. The radiation influences the erosion rate of nonmetallized propellant more than the metallized one, mainly due to the different erosion regimes, kinetically controlled for the former and diffusion controlled for the latter.
Journal of Propulsion and Power, 2013
Aerospace Science and Technology, 2013
ABSTRACT In the present study, surface mass and energy balances have been implemented in the abla... more ABSTRACT In the present study, surface mass and energy balances have been implemented in the ablative boundary condition of a two-dimensional full Navier–Stokes solver, to take into account the pyrolysis gas injection. A finite-rate ablation model is used, with steady-state ablation approximation to obtain the surface temperature. With this approximation, the conductive heat flux entering the wall is directly computed without a coupling with a solid conduction solver and the pyrolysis gas mass flow rate is a known fraction of the char mass flow rate. Simulations of carbon–phenolic solid rocket motor nozzle have been carried out to validate the model and to investigate the role of the most uncertain parameters. Results show the influence of the pyrolysis gas composition and of the ratio between pyrolysis gas and char mass fluxes, over the final erosion.
Uploads
Papers by Alessandro Turchi