Direct numerical simulations of small disturbances in the classical Stokes layer

Direct numerical simulations are used to investigate the stability characteristics of the classical semi-infinite Stokes layer that is generated by an oscillating flat plate. The calculations are based upon a velocity–vorticity formulation of the governing equations which allows efficient tracking of the time evolution of disturbances. The neutral-stability curve for two-dimensional disturbances was computed and found to agree well with the predictions of earlier semi-analytical studies. Further previously determined properties of two-dimensional disturbances in a Stokes layer were also compared to the results obtained by direct numerical simulation. The two-dimensional neutral stability results were then used to validate the extension of the direct numerical solution code to three-dimensional disturbances in the form of oblique waves.