Ae ABSTRACT The development of linear perturbations within laminar boundary layers subjected to a full range of adverse and favourable pressure gradients has been predicted numerically. Comparison of the predictions with published flow visualisation results enabled identification of the perturbation regions associated with the turbulent spot, trailing vortex streaks and oblique waves along the spot flanks. The effect of streamwise pressure gradient on spot characteristics (spot leading and

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... ing edge velocity, calming region trailing edge velocity and spot spreading half angle) was determined and was found to be consistent with published experimental data. The new data extends the range to severe adverse pressure gradient (separation) and to stronger favourable gradients. Correlations for the spot characteristics are provided. NOMENCLATURE Fluctuating pressure Re (a -18 ) Boundary layer Reynolds number Time Dimensionless time Time mean velocity in streamwise direction Freestream time mean velocity Uc