Numerical Simulation of Riblet Controlled Spatial Transition in a Zero-Pressure-Gradient Boundary Layer |
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Authors: | Stephan Klumpp Matthias Meinke Wolfgang Schröder |
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Institution: | 1.Institute of Aerodynamics,RWTH Aachen University,Aachen,Germany |
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Abstract: | To analyze the fundamental physical mechanism which determines the damping effect of a riblet surface on three-dimensional
transition several numerical simulations of spatial transition in a flat plate zero-pressure-gradient boundary layer above
a riblet wall are performed in this study. Two types of forced transition scenarios are investigated. The first type of transition
is defined by K-type transition induced by a dominant two-dimensional Tollmien–Schlichting (TS) wave and a weak spanwise disturbance.
The second type of transition is purely excited by two oblique waves. By a qualitative analysis of the occurring maximum wall-normal
and spanwise velocity components and the Fourier modes of the disturbances the two-dimensional TS waves are found to be amplified
by riblets, whereas three-dimensional structures, i.e., Λ-, hairpin, and streamwisely aligned vortices, are damped. At oblique transition the breakdown to turbulence is delayed by
the riblets compared to transition on a clean surface. The investigation of the near wall flow structure reveals secondary
flows induced by the riblets and reduced wall normal ejections as well as a reduced downwash. |
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