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Drag Reduction by Blowing and Creating a Film of a Secondary Lower Viscosity Fluid-Large Eddy Simulation

Ghaffarian, Ali | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39718 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Taeibi Rahni, Mohammad; Ramezanizadeh, Mahdi
  7. Abstract:
  8. Drag reduction is one of the most important topics in aerodynamics. Several techniques have been represented to reduce this force, such as surface roughness reduction, blowing, suction, cooling the fluid, etc. Blowing and creating a film of a secondary lower viscosity fluid is the technique used here. In our computations, we used large eddy simulation approach considering viscosity ratio variations effects. Investigations were performed for multiple squared cross sectional jets inclined normally into a turbulent cross flow. Each jet generates a pair of counter rotating vortex pair (CRVP) at its downstream while entering the cross flow. Two horseshoe vortices and a couple of wake vortices are also generated. In our LES, two subgrid scale models, namely Smagorinsky and WALE were used. The Results, including mean velocity components, shear stresses, and turbulent kinetic energy at different planes after the jet exit were compared with experimental and computational results of Ajersch et al. (1997). Then, jet viscosity variation effects on the wall friction drag were investigated. It was observed that decrease in viscosity ratio significantly results in wall friction drag reduction. On the other hand, viscosity ratio increase significantly enhances wall friction drag.

  9. Keywords:
  10. Drag Reduction ; Large Eddy Simulation (LES) ; Blowing ; Subgrid Scales ; Skin Friction Drag Coefficient ; Viscosity Ratio

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