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Erosion in a 90 degree Knee CFD Simulation

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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.

O-Grid Mesh

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.

Solver settings:
Type: Pressure-based
Velocity formulation: Absolute
Time setting: Steady State
Model: k-epsilon realizable
Near-Wall treatment: Enhanced Wall Treatment
Boundary conditions: Inlet velocity : 23 m/s

Outlet pressure : 0 psi

Wall: No-slip

Enable All Erosion Models

Solution methods: SIMPLE
Pressure interpolation scheme: Standard treatment
Momentum: Second-Order Upwind
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
Physical Models: Erosion/Accretion
Accuracy Control: 1e-5
Max.Refinement: 20
Tracking Scheme Selection: Trapezoidal
Injection type: Surface velocity inlet
Diameter Distribution: uniform
Diameter: 0.15mm
Total flow rate: 0.04627kg/s
Drag law: Spherical
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
Initialize: Hybrid
Residual Tolerance: 9e-4
Material used :
Pipe: Carbon steel

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

CFD Simulation

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.

There is a mesh file in this product. By the way, the Training File presents how to solve the problem and extract all desired results.


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