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Experiments in Fluids

, Volume 52, Issue 1, pp 11–21 | Cite as

Sensitivity of an asymmetric 3D diffuser to vortex-generator induced inlet condition perturbations

  • S. GrundmannEmail author
  • E. L. Sayles
  • Christopher J. Elkins
  • J. K. Eaton
Research Article

Abstract

Modifications of the turbulent separated flow in an asymmetric three-dimensional diffuser due to inlet condition perturbations were investigated using conventional static pressure measurements and velocity data acquired using magnetic resonance velocimetry (MRV). Previous experiments and simulations revealed a strong sensitivity of the diffuser performance to weak secondary flows in the inlet. The present, more detailed experiments were conducted to obtain a better understanding of this sensitivity. Pressure data were acquired in an airflow apparatus at an inlet Reynolds number of 10,000. The diffuser pressure recovery was strongly affected by a pair of longitudinal vortices injected along one wall of the inlet channel using either dielectric barrier discharge plasma actuators or conventional half-delta wing vortex generators. MRV measurements were obtained in a water flow apparatus at matched Reynolds number for two different cases with passive vortex generators. The first case had a pair of counter-rotating longitudinal vortices embedded in the boundary layer near the center of the expanding wall of the diffuser such that the flow on the outsides of the vortices was directed toward the wall. The MRV data showed that the three-dimensional separation bubble initially grew much slower causing a rapid early reduction in the core flow velocity and a consequent reduction of total pressure losses due to turbulent mixing. This produced a 13% increase in the overall pressure recovery. For the second case, the vortices rotated in the opposite sense, and the image vortices pushed them into the corners. This led to a very rapid initial growth of the separation bubble and formation of strong swirl at the diffuser exit. These changes resulted in a 17% reduction in the overall pressure recovery for this case. The results emphasize the extreme sensitivity of 3D separated flows to weak perturbations.

Keywords

Secondary Flow Separation Bubble Vortex Generator Baseline Case Pressure Recovery 
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.

Notes

Acknowledgments

We gratefully acknowledge the financial support of several organizations. Sven Grundmann was supported by a fellowship from the DAAD (German Academic Exchange Service) and Emily Sayles was supported by a National Defense Science and Engineering Graduate Fellowship and a Stanford Graduate Fellowship. Research expenses were supported by Siemens Power Generation.

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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • S. Grundmann
    • 1
    Email author
  • E. L. Sayles
    • 2
  • Christopher J. Elkins
    • 2
  • J. K. Eaton
    • 2
  1. 1.Center of Smart InterfacesTechnische Universität DarmstadtGriesheimGermany
  2. 2.Stanford UniversityStanfordUSA

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