Intercalibration Results. Numerical Rebuilding of Ablative Test Cases using KCMA
Start Date
3-3-2011 9:40 AM
Description
In the frame of its activities NASA as defined a one dimensional test case for assessing the capabilities of numerical tools dedicated to ablation. The objective of the test case is to compare in-depth ablation physics available in ablation codes. The test case focuses on a pyrolysing material without surface recession.
The current test case will be rebuilt using KCMA which has already been used for the similar efforts carried out in the frame of the European Ablation Working Group for the reconstruction of experimental measurements performed for graphite and carbon phenolic.
KCMA is based on a one dimensional approach and uses a surface energy balance at the material surface. It is based on a finite difference centred scheme accurate to the first order in time and the second order in space is used for solving the equations, and can compute TPS recession for stagnation point and cone configurations (for a dedicated point).
Several balance equations are solved for the gas and solid phases:
- The solid density accounting for pyrolysis;
- The gas density, taking into account pyrolysis, material porosity, changes of gas density under pressure effects, blockage;
- Gas momentum equation;
- Total energy conservation.
Porosity and gas friction within the material can be accounted for. The wall temperature and the mixture composition are calculated using the hypothesis of a wall at chemical equilibrium, and the surface temperature can be also imposed. Species mass fraction, temperature and density in the boundary layer are computed using the method of Gordon & Mc Bride and the data of JANNAF and/or Gurvich for computing the species specific heat, enthalpy and free entropy.
So far different materials can be handled by the tool. Carbonaceous materials, with and without pyrolysis, in this case carbon oxidation and sublimation are considered, while nitridation is not considered. The tool capabilities have been recently extended to silica based materials and melting of silica is taken into account for calculating the recession.
The results provided by the tool have been compared with the results obtained during the Pioneer-Venus mission, and the experimental data available for graphite and carbon phenolic. In the final contribution, numerical results on temperature distribution inside the material and char thickness for the defined test case will be predicted.
Intercalibration Results. Numerical Rebuilding of Ablative Test Cases using KCMA
In the frame of its activities NASA as defined a one dimensional test case for assessing the capabilities of numerical tools dedicated to ablation. The objective of the test case is to compare in-depth ablation physics available in ablation codes. The test case focuses on a pyrolysing material without surface recession.
The current test case will be rebuilt using KCMA which has already been used for the similar efforts carried out in the frame of the European Ablation Working Group for the reconstruction of experimental measurements performed for graphite and carbon phenolic.
KCMA is based on a one dimensional approach and uses a surface energy balance at the material surface. It is based on a finite difference centred scheme accurate to the first order in time and the second order in space is used for solving the equations, and can compute TPS recession for stagnation point and cone configurations (for a dedicated point).
Several balance equations are solved for the gas and solid phases:
- The solid density accounting for pyrolysis;
- The gas density, taking into account pyrolysis, material porosity, changes of gas density under pressure effects, blockage;
- Gas momentum equation;
- Total energy conservation.
Porosity and gas friction within the material can be accounted for. The wall temperature and the mixture composition are calculated using the hypothesis of a wall at chemical equilibrium, and the surface temperature can be also imposed. Species mass fraction, temperature and density in the boundary layer are computed using the method of Gordon & Mc Bride and the data of JANNAF and/or Gurvich for computing the species specific heat, enthalpy and free entropy.
So far different materials can be handled by the tool. Carbonaceous materials, with and without pyrolysis, in this case carbon oxidation and sublimation are considered, while nitridation is not considered. The tool capabilities have been recently extended to silica based materials and melting of silica is taken into account for calculating the recession.
The results provided by the tool have been compared with the results obtained during the Pioneer-Venus mission, and the experimental data available for graphite and carbon phenolic. In the final contribution, numerical results on temperature distribution inside the material and char thickness for the defined test case will be predicted.