Lubrication Effect on Piston-Ring Pack Friction
The present problem simulates the lubrication process effect on friction factor in the space between the cylinder and the ring in an engine considering various groove texture patterns.
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Lubrication Project Description
The present problem simulates the lubrication process effect on friction factor in the space between the cylinder and the ring in an engine considering various groove texture patterns. In fact, the movement of the ring on the inner surface of the cylinder of an engine causes friction between the surfaces. Lubrication process can be used to reduce friction between surfaces; In this way, oil is poured in the space between these two surfaces. The oil in this model has a density equal to 900 kg.m-3, specific heat capacity equal to 210 j.kg-1.K-1, thermal conductivity equal to 0.13 Wm-1.K-1 and viscosity equal to 0.04 kg .m-1.s-1.
On the inner surface of the cylinder, there are grooves where the oil flows in the space between these grooves. These surfaces can be designed with different patterns based on the angle and density of the grooves placed on them. In the present modeling, four different patterns have been used for these grooves, including 30, 45, 60 and 90 degree angles. The aim of the present project is to investigate the amount of friction coefficient produced on the moving surface of the ring. In the present simulation, a square computational area is defined in which several rows of grooves with the mentioned angles are designed.
Lubrication Project Description
The lower surfaces of this area and its grooves are defined as a static wall and the smooth upper surface of the area is defined as a moving wall. Since this square area is defined as a sample space of a general computational area, the lateral surfaces of the grooves have a symmetric boundary condition. The lower stationary wall has a constant temperature of 353 K and the upper moving wall has a constant temperature of 393 K. Due to the fact that the modeling is done in four different patterns based on the angle of the grooves, the oil flow path inside these grooves will be different.
Now, considering that when a high moving surface moves on these grooves, the path of movement of this surface with the grooves creates an angle equal to half the angle between the two grooves; Therefore, the bisector of the mentioned angles is used to define the amount of velocity of the moving wall relative to its side grooves. This moving wall in all four modes has a velocity equal to 10 m.s-1, which using the sine and cosine of angles of 15, 22.5, 30 and 45 degrees can have different velocities in two different coordinate directions.
Geometry & Mesh
The current model is designed in three dimensions using Design Modeler software. The model includes a square computational area with a side of 0.001 m for fluid flow. This computational area has 20 rows of grooves with a depth of 0.000006 m. These rows of grooves are designed in two different directions and make different angles to each other. These grooves are designed based on the angle of relation to each other, with four different patterns, which include modes with angles of 15, 30, 45 and 90 degrees.
The meshing of the present model has been done using ANSYS Meshing software. The mesh type is structured and the element number in grooved modes with angles of 30, 45, 60 and 90 degrees is equal to 633774, 645574, 642332 and 692403, respectively. The following figure shows a view of the mesh for the 60 ° groove mode.
Lubrication CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is steady.
- The gravity effect on the fluid is ignored.
A summary of the defining steps of the problem and its solution is given in the following table:
|near wall treatment||standard wall functions|
|wall motion||moving wall|
|wall motion||stationary wall|
|momentum||second order upwind|
|energy||second order upwind|
|turbulent kinetic energy||first order upwind|
|turbulent dissipation rate||first order upwind|
At the end of the solution process, three-dimensional contours related to pressure, velocity, and temperature, as well as a two-dimensional friction coefficient contour and plots are obtained.
Y+ (Y plus)
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.