Experimental and Numerical Investigation of Three-Dimensional Laminar Wall Jet of Newtonian and Non-Newtonian Fluids.

摘要

A research program was designed to investigate the characteristics of three-dimensional laminar wall jet flow of both Newtonian and two shear-thinning non-Newtonian fluids. The non-Newtonian fluids were prepared from xanthan gum solutions of various concentrations. Both experimental and numerical methodologies were employed in this study. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open fluid tank. The initial Reynolds numbers based on the pipe diameter and jet exit velocity ranged from 250 to 800. The velocity measurements were conducted using a particle image velocimetry technique. The measurements were conducted at several streamwise locations to cover both the developing and self-similar regions. For the numerical study, the complete nonlinear Navier-Stokes equation was solved using an in-house colocated finite volume based CFD code. A Carreau model was employed for the non-Newtonian fluids. The viscosity in the governing equations was obtained explicitly.;From the PIV measurements and CFD results, velocity profiles and jet half-widths were extracted at selected downstream locations to study the effects of Reynolds number and specific fluid type on the jet characteristics. It was observed that the numerical results are in reasonable agreement with the experimental data The decay of maximum velocity, jet spread rates, skin friction coefficient, streamwise velocity profiles, and secondary flows depend strongly on the initial Reynolds number irrespective of the fluid. The results also show that the jet spreads more in the spanwise direction than in the transverse direction in the early flow development whereas the reverse is true in the downstream region. Important differences were observed when the results for the non-Newtonian fluids were compared with those for Newtonian fluid.