Wall shear rate in the Taylor–Couette–Poiseuille flow at low axial Reynolds number

An experimental investigation was done by the use of visual observations and the electrochemical technique in order to study the appearance of hydrodynamic instabilities at low Reaxg in the gap between two coaxial cylinders, with radius ratio Rr/Rs=0.615 and aspect ratio L/e=24. A motor drove the inner cylinder and the outer cylinder was fixed. A Newtonian fluid (Emkarox HV45) and two non-Newtonian fluids (aqueous solutions of guar and CMC) have been used. The analysis of the evolution of the size of the Taylor vortices is carried out for Reaxg<4.0. For Reaxg<2 we showed that the vortices underwent a contraction phase up to Tag≈80, and a stretching phase for Tag>80. For higher Reaxg, the contraction phase vanished and the vortices progressively stretched with increasing Tag. A dimensionless representation was also proposed for wall friction generalized to non-Newtonian fluids following the Ostwald law.