Efeitos viscosos em cilindros imersos em fluidos não-newtonianos

Abstract

The approximation dueto Pohlhausen for the velocity profile within the boundary layer was used to solve the problem of a bi-dimensional interface immersed in a non-Newtonian fluid, whose rheological behaviour can be described by the power law model. Arbitrary values of the flow behaviour index (n) were considered and results for three different values are presented, including the case of a Newtonian fluid (n=1). It was assumed that a slip condition can occur at the interface. The slip condition at the interface was introduce through a dimensioless parameter, k, which is defined as the ratio between the slip velocity and the free stream velocity. Results were also obtained for the flow pasta solid surface where no-slip condition is assumed. Relevant physical quantities of the boundary layer such as displacement thickness, momentum thickness and drag coefficient were calculated as functions of the various flow parameters. Extrapolated values of the angle of separation for the case of a Newtonian fluid, showed excellent agreement with the literature, namely, the values are around 108°, for all values of k considered. Under the same conditios, the results for non-Newtonian fluids are around 119°, thus showing the influence of the rheological behaviour of the fluid.