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The objective of this work is to simulate the pipe flow using (k-ω) turbulence model and compare it with the experimental correlations from the literature. The (k-ω) model is chosen over the (k-Ɛ) model because, the latter has a tendency to poorly compute the flows involving separation, huge pressure gradients and strong streamline curvature along the flow. The inlet condition is a fully developed, laminar flow (ensured by sufficiently long pipe). The model is simulated for wall distribution function to predict separation and velocity of the turbulent flow near the wall, streamline to predict the vortices formed and the velocity profile, pressure profiles at the bends. The model was analyzed using COMSOL Multiphysics Single-Phase Fluid Solver for Turbulent Flows (k-ω) model. This model also helps us understand the corrosion and erosion that takes place in pipelines due to turbulence in it.
Cross Section of the Baseline CAD model of the Elbow Bend Pipe
Entire geometry is separated into 3 regions - inlet on the bottom part, Elbow region, Outlet region on the top.
Initial test result of flow through a long channel equal to the length of the inlet section to assertain a fully developed flow in the pipe. It is confirmed by the following graph that shows a very low wall resolution of around 13 at the outlet.
The velocity field is represented by the streamline and color profile. The streamline traces the path of the fluid flow. The fluid flow is laminar and fully developed at the bottom region while 2 counter rotating vortex fields can be noticed (one is invisible or below the top vortex).
Mesh Model of the Pipe with Elbow bend. The mesh element size is refined to extra fine in the elbow region while the inlet and outlet regions are mapped and swept. A boundary layer of 8 quads is generated to capture and compute details at the walls. The elbow region is meshed with free tetrahedron elements.
A cut section of the velocity magnitude depicts the changes in the parameter after the bend near the wall after the bend region. This is an evident proof for the presence of vortex.
Wall resolution studied at the flow walls show increase in the viscous units after the bend.
The animation depicts the pressure profile in the elbow during the flow.
It is evident that the outer radius of the bend undergoes a large pressure gradient increase while there is a drop in the inner radius of the bend. This gradient results in a turbulence causing vortex as the water leaves the bend into the exit domain and pressure is normalized.
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