Computational Investigation of Sensitivity of the Crossflow Instability to Two-Dimensional Surface Imperfections
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The interaction between two-dimensional steps and gaps with stationary crossﬂow vortices on a swept laminar wing has been investigated using computational methods. Using ﬂow conditions as experienced in complementary experiments using the SWIFTER and SWIFTEST airfoils as found in ﬂight and as installed in the KSWT facility, the growth of stationary crossﬂow disturbances were calculated using direct simulation. Forward-facing steps were found to amplify stationary crossﬂow waves signiﬁcantly once a threshold step height had been exceeded. This value was found to correlate well with experimentally observed movement of the transition front forward. A correlation based on a physical explanation of the mechanisms involved was proposed, and also was found to correlate well with the SWIFTER and SWIFTEST experimental observations. Backward-facing steps were found not to amplify stationary waves for step heights tested in the computational regime. Local stability analyses of the ﬂowﬁeld surrounding the backward-facing steps reveal the existence of a traveling mode similar to traveling crossﬂow vortices. A mechanism whereby this leads to transition to turbulence was hypothesized.
Tufts, Matthew W (2015). Computational Investigation of Sensitivity of the Crossflow Instability to Two-Dimensional Surface Imperfections. Doctoral dissertation, Texas A & M University. Available electronically from