Numerical and experimental studies of non-Newtonian fluids in cross-flow around a circular cylinder.

摘要

The numerical and experimental studies of non-Newtonian fluids flow around a circular cylinder have been carried out. For the numerical study, two purely viscous non-Newtonian fluids (a power-law fluid and a Carreau fluid) have been investigated. The SIMPLER algorithm is used in the numerical study. For the experimental study, a viscoelastic fluid (an aqueous polyacrylamide solution) was investigated.;The study on a Carreau fluid shows that the shear thinning effect is (1) to increase the wake size (consequently, the flow separation starts at a lower Reynolds number); (2) to decrease pressure and the friction coefficients and, (3) to enhance the heat transfer.;When the flow is in the "zero shear region" or the "infinite shear region", the influences of power-law index and Weissenberg number are small, the maximum Nusselt number is located at or very close to the stagnation point. When the flow moves into and out of the "power-law region", the maximum Nusselt number shifts away from and back to the front stagnation point. This indicates that this phenomenon is not due to viscosity going to infinity at the front stagnation point, the so-called "zero defect". It is hypothesized that this behavior is connected with the shear thinning of the fluid.;The experimental study on an aqueous polyacrylamide solution shows that the maximum Nusselt number is located at the front stagnation point. This suggests that the elasticity may shift the maximum Nusselt number back to the stagnation point. The average Nusselt number can be well predicted by either a power-law or a Carreau model, especially the Carreau model. This suggests that the elasticity may modify the local heat transfer distribution, but it has a minimum influence on the average heat transfer.;The numerical study on a power-law fluid shows that the shear thinning effect is (1) to delay the flow separation, however, the separation angle increases faster than a Newtonian fluid as the Reynolds number increases; (2) to increase the pressure coefficient and decrease the friction coefficient and, (3) to enhance the heat transfer.