Stability of a boundary layer flow in the wake of a medium height roughness element

Plogmann, Benjamin; Wuerz, Werner; Kraemer, Ewald

doi:10.2514/6.2014-2886

Cited by 3 publications

(1 citation statement)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In compliance, it is seen, that the 2D and quasi 2D fundamental modes recover linear stability characteristics, so that their superimposed amplitude growths considerably less (compared with the near wake) or even decreases slightly as observed in the centerline region ( Fig. 3a and also Plogmann et al 21 ). That is, the resonant mode interactions become weaker in the far wake with the less distinct growth/decay of the driving 2D and quasi 2D fundamental modes.…”

Section: Resonant Mode Interactions In the Low-frequency Subharmonicsupporting

confidence: 54%

Nonlinear Mode Interactions in the Wake of a Medium Height Roughness Element

Plogmann¹,

Würz²,

Krämer³

2015

Procedia IUTAM

Self Cite

View full text Add to dashboard Cite

The present study is devoted to nonlinear (resonant) mode interactions in the wake of a medium height, cylindrical roughness element, which is placed in a laminar, airfoil boundary layer. The roughness element causes a considerable mean flow distortion in the near wake centerline region and two counter-rotating vortex pairs arise in the outer spanwise domain. In the streamwise evolution the mean flow stabilizes and a spanwise uniform flow is recovered in the far wake. Upstream of the roughness controlled, low-amplitude Tollmien-Schlichting (TS) wave modes are excited in the upper branch unstable region. The interference of the excited, 2D fundamental modes with the roughness results in the excitation of oblique modes in a broad spanwise wave number range. Nonlinear interactions in-between the (oblique) fundamental modes in the destabilized near wake lead to the generation of primary, low-frequency modes at the difference frequencies of the fundamental modes, before the fundamental modes can recover linear stability characteristics in the far wake. In contrast, the primary, subharmonic-type modes experience a nonlinear growth, which is a result of frequency and spanwise wave number detuned resonant mode interactions with the 2D fundamental modes. The resonant growth of the primary interaction modes initiates a symmetrization of the spectrum in the low-frequency, subharmonic range. That is, symmetric subharmonic-type (secondary) modes are resonantly amplified in the far wake. Therefore, although the fundamental modes recover linear stability characteristics with the stabilization of the mean flow, resonant mode interactions in the low-frequency, subharmonic range initiate the onset of boundary layer transition in the far wake of the medium height roughness element.

show abstract

Section: Resonant Mode Interactions In the Low-frequency Subharmonicsupporting

confidence: 54%