Erosion in a 90 degree Knee CFD Simulation
Erosion is one of the problematic industrial phenomena. It can be said that erosion and transport pipeline lifetime are important factors in related industries.
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Since no fluid (especially in industrial applications) is pure, there are generally different particles in a flow that are transported by fluid. In general, these impurities are constantly shifting in the core of the flow. This is not a problem in a straight-ahead pipe. But when the fluid redirects, these impurities cannot redirect with the fluid. This causes local independence of solid particles from the fluid in pipelines, resulting in the impact of heterogeneous particles on the body of the fluid pipelines and erosion, consequently.
Unfortunately, in almost all industrial applications the fluid is not pure, so the phenomenon of erosion causes problems in the transport pipeline. Also, an issue that reinforces this event is the amount of flow turbulence. The more turbulent the flow, the greater the momentum flowing by the particles. The impacts on the transmission pipeline are greater when the flow changes direction, resulting in more erosion. In addition to the turbulence of the flow, other factors such as particle size, the rate of particle flow redirection, the number of particle impacts to the surface and the flow rate also influence the amount and profile of the erosion. The other endpoint is that the place of erosion is usually where the flow redirects. This is precisely why the erosion profile at the knees is generally examined by fasteners and joints.
The beginning of each simulation starts with designing the computational domain. Despite the geometry is a knee joint, it has to be divided into different sections in order to produce a structured mesh. Each segment has individually meshed so that the boundary layer settings are well implemented. the 3-D geometry is designed by ANSYS Fluent software.
The mesh is done by ANSYS Meshing software. The computational domain is divided into 4 parts, and structured mesh is used for each segment. The benefits of a structured mesh include increased CFD simulation speed and accuracy. This is especially important for issues such as checking the erosion profile because, in addition to the boundary layer, path lines and particle tracking should be well observed when moving along the knee section. The element number is 4,319,695. Since the mesh was sufficiently fine-grained, the Enhanced-Wall-Treatment method was applied instead of Wall-Function for boundary layer estimation. One of the benefits of this method is the high accuracy of the results in boundaries.
Erosion CFD Simulation
The settings made in the Fluent software are shown in the following table.
|Time setting:||Steady State|
|Near-Wall treatment:||Enhanced Wall Treatment|
|Boundary conditions:||Inlet velocity : 23 m/s
Outlet pressure : 0 psi
Enable All Erosion Models
|Pressure interpolation scheme:||Standard treatment|
|Turbulent kinetic:||First Order Upwind|
|Turbulent dissipation:||First Order Upwind|
|Multi-phase settings (DPM) :|
|Discrete phase model||Enabled|
|Interaction with continuous phase:||10 continues phase iteration per DPM|
|Max step tracking:||50000|
|Step length factor:||Default 5|
|Tracking Scheme Selection:||Trapezoidal|
|Injection type:||Surface velocity inlet|
|Total flow rate:||0.04627kg/s|
|Turbulent Dispersion:||Stochastic Tracking
Discrete Random Walk Model
Random Eddy Lifetime
Number of Tries 10
Time Scale Constant 0.3
|The number of particles tracked:||1406|
|Material used :|
The density of 7990 kg/m3
|Continuous phase:||Natural Gas fluid
Density of 0.65 kg/m3
viscosity of 0.00013 pas.s
|Discrete phase:||The density of 2650 kg/m3|
Another important point to consider is that the length of the pipe must be long enough to develop the flow before reaching the knee joint. Otherwise, the particle density in the flow may produce unrealistic results.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.