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Experimental Investigations of Controlled Transition in a Laminar Separation Bubble at an Axisymmetric Diffuser

  • L. Hoefener
  • W. Nitsche
Conference paper
Part of the Notes on Numerical Fluid Mechanics and Multidisciplinary Design (NNFM) book series (NNFM, volume 96)

Abstract

Results of an experimental study of controlled laminar-turbulent transition in a smooth axisymmetric diffuser at 7800 < Re D1 < 10600 based on the inlet diameter D 1 and the bulk velocity \( u_m = \tfrac{2} {{D_1 }}\int_0^{D_1 /2} {u(r)dr} \) are presented. The inlet flow is an incompletely developed laminar pipe flow with a clear boundary-layer shape (boundary layer thickness δ99/D1 ≤ 0.3). The smooth diffuser contour causes the formation of a closed pressure-induced laminar separation bubble, which is notedly receptive for small-scale disturbances. Upstream of the diverging geometry, controlled periodic perturbations are introduced into the boundary layer. The instability of the local velocity profiles with an inflection point causes a massive growth of instability waves within the shear layer leading to a turbulent breakdown of the laminar flow. For two different perturbation modes, the resulting mean flow field as well as the velocity fluctuations are measured by means of a Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) system in detail.

Keywords

Particle Image Velocimetry Shear Layer Recirculation Zone Separation Bubble Laminar Boundary Layer 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2007

Authors and Affiliations

  • L. Hoefener
    • 1
  • W. Nitsche
    • 1
  1. 1.Institute for Aeronautics and Astronautics (ILR)Technical University BerlinBerlinGermany

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