Sensitivity Analysis and Uncertainty Quantification of Plasma Jet Instabilities in the VKI Plasmatron

The VKI’s Plasmatron facility can reproduce the high-enthalpy gas flow encountered during the entry of a spacecraft into a planetary atmosphere and thus allows to test thermal protection materials used for the heat shield of the vehicle. However, the jet generated by the facility undergoes instability phenomena, which must be investigated for a correct characterization of the freestream flow and interpretation of the thermal response of the material under study.

The overarching objective of this final-year project is to study the influence of thermodynamic and transport properties of the plasma jet on the instability features of this plasma jet in order to better understand the mechanisms involved. We first perform a sensitivity analysis of the instability features of the plasma jet. The varying parameters are the thermodynamic and transport properties while operating conditions of the Plasmatron are assumed to be fixed and deterministic. Then, because the electric power that is actually transferred by the Plasmatron to the plasma jet is not precisely known, the electric power is assumed to be uncertain and is characterized by a random variable. A stochastic collocation method is implemented to propagate the uncertainty introduced by the electric power to the instability features of the plasma jet. Finally, the sensitivity analysis is carried out again, this time however as a stochastic sensitivity analysis that accounts for the uncertainty in the electric power.

Results indicate that the compressibility factor has a dominant influence affecting all instability modes. Furthermore, we identify for each instability mode additional thermodynamic and transport properties that determine its instability features; in particular, it is shown that the vortical mode is influenced mainly by the viscosity parameter, while acoustic modes are mainly driven by the enthalpy of the gas.