Turbulent Structures of Non-Newtonian Solutions in Taylor-Couette Flow

• Author / Creator

  Li, Haozhe

• The turbulent structures of Taylor-Couette (T-C) flow of a Polyacrylamide (PAM) solution
  (200 and 400 ppm) is experimentally investigated and compared with the same flow with
  water at Re = 1.50 × 104, to understand the effect of nonlinear shear-thinning viscosity on
  the flow regime, in terms of turbulence statistics, coherent structures, turbulence production,
  and viscous dissipation. The turbulent Taylor-Couette (TTC) flow regime is achieved and
  driven by inner cylinder rotation (outer cylinder stays stationary). Velocity measurements
  are conducted by employing Stereoscopic-Particle Image Velocimetry (SPIV) to obtain three
  velocity components within a rectangular field of view (FOV) in radial-axial (r − z) (merid-
  ional) plane, and the torque acted on the inner cylinder is recorded to obtain skin friction
  coefficient Cf,l.
  The torque measurements show that with the addition of shear-thinning polymer, 41%
  and 52% drag reduction is achieved for 200 ppm and 400 ppm solutions both under Re =
  1.50 × 104, respectively. The velocity measurement of the in-plane velocity shows that the
  motions of non-Newtonian Taylor vortices are more flexible compared to the Newtonian case
  in both the axial and radial direction induced by the shear-thinning effect. The turbulence
  statistics show that wall-normal (r) and spanwise (z) Reynolds normal stresses are signif-
  icantly attenuated and smeared out across the bulk domain as the concentration of shear-
  thinning polymers increases. The radial jet (both inner and outer jets) intensity is reduced
  with the addition of shear-thinning polymer. Snapshot Proper Orthogonal Decomposition
  (POD) of in-plane velocity fluctuations field shows that vortical-shape fluctuations are the
  dominant energetic structures for both Newtonian and non-Newtonian T-C flows that sta-
  tistically contribute to most of the turbulence kinetic energy (TKE) for both Newtonian and
  non-Newtonian fluids. The shear layer structure changes due to the shear-thinning effect,
  which is reflected by the second POD mode. The Snapshot POD of the azimuthal veloc-
  ity fluctuation field captures energetic structures at locations where turbulence is generated
  and the shear-thinning effect is pronounced. With the addition of shear-thinning polymer,
  the energetic structures are compressed closer to the wall, and the bulk flow becomes less
  important in terms of contributing to turbulence production.
  The spatial correlation analysis of the in-plane velocity fluctuations shows that the shear-
  thinning polymer enhances the space correlation compared to the Newtonian fluid. Anti-
  correlation is found more pronounced than the Newtonian case in the axial direction, which
  leads to a reduced magnitude of axial integral lengthscale L33. The 2D energy spectrum
  shows that the Kolmogorov -5/3 law does not hold for T-C turbulence for both Newtonian
  and non-Newtonian fluids. Non-Newtonian energy spectrum based on radial and azimuthal
  fluctuations shows an increased importance of large-scale structures and a decreased im-
  portance of motions at small lengthscales in terms of energy containment. The dissipation
  spectrum shows increased contribution for dissipation at smaller lengthscales as concentra-
  tion increases.

• Subjects / Keywords

  • Turbulent Structures
  • Non-Newtonian Solutions

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-9mpt-5r96

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.