ISSN Online: 2379-1748
ISBN Flash Drive: 978-1-56700-483-0
ISBN Online: 978-1-56700-482-3
4th Thermal and Fluids Engineering Conference
NUMERICAL STUDY OF THE SECONDARY FLOW FORMATION OF A FLUID PASSING THROUGH A 90° ELBOW WITH SQUARE CROSS SECTION
Abstract
This paper studies the fluid dynamics behavior of a single-phase flow passing through a 90° elbow with a square cross section. The main objective was to deepen the understanding of the initiation of secondary flows formed in the flow when passing through the elbow. A three-dimensional numerical model was developed using COMSOL 5.1 Multiphysics. Geometry of the model consisted in a 0.0254 m square pipe with 1 m inlet, an elbow with dimensionless radius of curvature of 1 and 2.5 and a 1 m long outlet pipe. The Reynolds number was varied with
values of 100 for laminar flows, and 100,000 for turbulent flow. All turbulent flow simulations were performed using k-epsilon turbulence model. Two important modifications were made to the simulations to observe their effect in the secondary flows, which lead to important findings. First, an artificial external acceleration (as a body force) was introduced in the opposite direction to the natural centrifugal acceleration. Second, the boundary condition at the elbow and/or pipe walls was changed from non-slip to slip. It was found that imbalances in the pressure gradient within cross-sectional planes arisen from the velocity boundary layer are responsible for the
initiation of secondary flows, in addition to the existence of a centrifugal acceleration. The imbalances are due to
the non-slip wall condition, which plays a decisive role.