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Linear stability analysis is performed using a combination of two-dimensionalDirect Simulation Monte Carlo (DSMC) method for the computation of the basicstate and solution of the pertinent eigenvalue problem, as applied to thecanonical boundary layer on a semi-infinite flat plate. Three different gasesare monitored, namely nitrogen, argon and air, the latter as a mixture of 79\%Nitrogen and 21\% Oxygen at a range of free-stream Mach numbers correspondingto flight at an altitude of 55km. A neural network has been utilised to predictand smooth the raw DSMC data; the steady laminar profiles obtained are in verygood agreement with those computed by (self-similar) boundary layer theory,under isothermal or adiabatic wall conditions, subject to the appropriate slipcorrections computed in the DSMC method.  The leading eigenmode results pertaining to the unsmoothed DSMC profiles arecompared against those of the classic boundary layer theory. Smallquantitative, but no significant qualitative differences between the results ofthe two classes of steady base flows have been found at all parametersexamined. The frequencies of the leading eigenmodes at all conditions examinedare practically identical, while perturbations corresponding to the DSMCprofiles are found to be systematically more damped than their counterpartsarising in the boundary layer at the conditions examined, when the correctvelocity slip and temperature jump boundary conditions are imposed in the baseflow profiles; by contrast, when the classic no-slip boundary conditions areused, less damped/more unstable profiles are obtained, which would lead theflow to earlier transition. On the other hand, the DSMC profiles smoothed bythe neural network are marginally more stable than their unsmoothedcounterparts.

Linear stability analysis of hypersonic boundary layers computed by a kinetic approach: A semi-infinite flat plate at Mach 4.5 and 9