Investigation of Galileo Probe Entry Heating with Coupled Radiation and Ablation - PowerPoint Presentation

1. Investigation of Galileo Probe Entry Heating with Coupled Radiation and AblationTom West, Aaron Erb, and Chris JohnstonNASA Langley Research Center

2. Galileo Probe OverviewJovian entry on 7 December 1995 traveling at 47 km/sSphere-cone with a 22.2 cm nose radius and a 44.86 degree half angle frustumCarbon phenolic TPS material (FM 5055G) adapted with opacified resin to mitigate radiative heatingForebody outfitted with 10 analog resistance ablation detector (ARAD) sensors and four thermistors28/13/2023

3. Pre-Flight Predictions vs Observed RecessionPre-flight predictions made by Moss and Simmonds in 1982Viscous Shock-Layer (VSL) solver with thermochemical equilibrium, coupled radiation (tangent slab) and ablation (steady-state equilibrium)Binary species diffusion with constant Schmidt numberFully turbulent using two-layer eddy viscosity model from CebeciFlowfield modeled with 11% He and 89% H by volumeMeasured recession returned from the 10 ARAD sensors showed:Likely overprediction of recession in the stagnation regionSignificant under prediction of recession on the flank38/13/2023

4. Previous Attempts to Reconcile ObservationsMatsuyama et al. (2005) performed thermochemical equilibrium analysis with coupled radiation and ablationTangent-slab and binary diffusion with constant ScInjection induced turbulence modelIncreased He to 13.6% by volume48/13/2023Deficiencies in Physics Modeling Led to Continued Disagreement with the Flight Data. Matsuyama et al. 2005Park (2009) analyzed the stagnation point with improved radiation absorption and spallationTangent-slab and binary diffusion with constant ScEmploys VSL code with adjusted nose radius to match shock standoffUses new modified JANAF coefficients Park 2009

5. Objectives and ApproachObjectivesRevisit Galileo forebody physics modeling approachesEmployer higher model fidelity beyond a “heritage” approach and relax significant assumptionsInvestigate the impact of parametric uncertainty and identify key driversModeling approaches InvestigatedCoupled ablationForebody shape change due to recession Three-dimensional radiationMulticomponent diffusionIonization potential loweringState-specific H modelingFlowfield ray-tracingFreestream Radiation Absorption58/13/2023

6. Coupled Ablation and TPS ModelingCoupled AblationIncrease shock standoff – massive blowing from the TPSLowers convective heatingStrongly absorbing species form in the boundary layer from ablation productsPartial blockage of incident radiative fluxForebody shape change due to recession Preliminary analysis showed the nose should blunt during the descentObserved nose sharpening leads to less radiative heating68/13/2023 = 22.2 cm  20.7 cm Non-AblatingAblatingNon-AblatingAblating

7. Impact of Diffusion ModelingPrevious studies assumed binary diffusion with constant Schmidt number – well suited for Earth and Mars entry modelingVastly different molecular weights of species prohibit this assumptionRigorous Stefan-Maxwell multicomponent diffusion modeled needed to relax assumptions – results in higher convective heating due to increased H diffusion78/13/2023Peak Heating (t = 53 sec)

8. Three-Dimensional Radiative Heating and H IonizationFlowfield-radiation coupling known to be importantTangent-slab is typically used for computing radiative heatingResults in about 10% over-prediction of forebody radiative heating compared to 3D radiation via ray-tracingH Ionization potential lowering High electron number density increases probability of H ionizationLowering the potential for H ionization leads to a 10% decrease in final recession88/13/2023

9. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recession98/13/2023

10. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recessionHeritage analysis (with coupled ablation and radiation) insufficient to accurately capture flight data108/13/2023

11. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recessionHeritage analysis (with coupled ablation and radiation) insufficient to accurately capture flight dataAccurate diffusion modeling greatly improves convective heating trend on the flank118/13/2023

12. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recessionHeritage analysis (with coupled ablation and radiation) insufficient to accurately capture flight dataAccurate diffusion modeling greatly improves convective heating trend on the flankRay-tracing for surface radiative heating lowers the radiative heating on the forebody128/13/2023

13. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recessionHeritage analysis (with coupled ablation and radiation) insufficient to accurately capture flight dataAccurate diffusion modeling greatly improves convective heating trend on the flankRay-tracing for surface radiative heating lowers the radiative heating on the forebodyIncluding forebody shape change due to ablation further improves prediction138/13/2023

14. SummaryPre-flight predictions:Overpredicted stagnation-point recessionUnderpredicted flank recessionHeritage analysis (with coupled ablation and radiation) insufficient to accurately capture flight dataAccurate diffusion modeling greatly improves convective heating trend on the flankRay-tracing for surface radiative heating lowers the radiative heating on the forebodyIncluding forebody shape change due to ablation further improves predictionUncertainty bounds capture the flight data and identify key sources of uncertainty that could be further investigated in the future148/13/2023

15. Questions?158/13/2023Further details…