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)


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.


Particle Image Velocimetry Shear Layer Recirculation Zone Separation Bubble Laminar Boundary Layer 
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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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