Simulation of Sloshing effect in Gearbox using Ansys fluent

AIM

     To analyze the sloshing of gears inside the gearbox due to the meshing of the gears for the fluids with different clearances between the gears. 

TASK 

     The four types of cases are done in this project using two fluids & two clearance between the gears. The two fluids selected for this simulation are water & oil.

Sloshing effect

   Sloshing refers to the movement of liquid inside another object. It is a complex phenomenon that refers to violent resonant fluid motion inside any object viz tank or container due to the sudden disturbance caused to the fluid during brakes & in turns. 

Procedure

• The User-defined function is commonly used in the industry to check whether the adequate lubricate is supplied to all gears for which the visual c++ compiler is used. 

• Open the SpaceClaim & import the file by drag and drop option.

                                                    a) Geometry

• Extract the fluid volume for the simulation by selecting the four circles of housing by using the option prepare --> volume extract

                                                   b) Volume extract

• The 2D geometry is created using design --> split body & choose the midplane & extracted volume & then select the faces to be removed then create a section view & copy-paste the section view in a new file. The 3D geometry file is closed to avoid errors during the simulation.                                                 c) 2D Geometry
• Open the mesh & set the mesh size to 3mm & under proximity set 1 cell across the gap to capture the meshing of the gears properly.                                                                                                                                           d) Mesh
• Create two named selection for the right & left gears using the edge tool option.                                                                                              e) Named selection
• Open the fluent i) Multiphase - volume of fluid.                                                                                       no of eulerian phases- 2.                                                                                           Formulation - Implicit. The implicit method is preferred over the explicit method since the stability of the equation is more in implicit.  
• Viscous model - i) k-epsilon with realizable & enhanced wall treatment is selected.
• The transient solver is selected since the fluid simulation for the gears is studied & gravity value is set to -9.81 m/s^2.
• Domain --> refine/coarse --> cell register --> new --> region & select the quad provide the values as below.                                                                                                 Xmin = - 0.05612             Xmax = 0.17112                                                               Ymin = -0.0675                Ymax = -0.0375.

                                                        f) Region

• User-defined --> function --> compile --> add, import the rate.c file & click on build, then load it.
• Domain --> dynamic mesh --> create/edit --> motion attributes --> left gear              CoG(0 0 0) & for the right gear CoG (0.115 0 0). Click on display zone motion to view the gear motion.

                                                              g) Zone motion

• Click on initial & select the patch --> water --> region 0 & set the value to 1.
• Create the contour & animation files for the water phases.                                                                                                                                 h) Contour plot                                                                                                                           
• Set the time step size - 1e-4 & no of steps - 1000. 
• Dynamic meshing --> remeshing i) min length scale - 1e-4.                                                                                        ii) max length scale - 2e-3.                                                                                        iii) max cell skewness - 0.7.                                                                                      iv) size remeshing interval - 5.

Water Lubricant

The general property of water its boiling point is 100 deg, cohesive fluid & has low viscosity value. The above property is not suitable for the lubrication purpose since fluid needs to stick to the object & viscosity to be high for proper contact & boiling point to be high to have a high operating range. 

                                      i) Water contour for smaller clearance

The water has a low viscosity of it can flow easily & due to the cohesive nature, it doesn\'t stick to the object. The water is thrown out at the top of the gears due to the centrifugal force caused due to the weak surface tension in the water & the meshing are less lubricated which will damage them. The lubricant must reach the bottom when the gears stop rotating due to the gravitational force which is essential in casing design to prevent fluid stagnation.

Oil Lubricant

The property of the oil makes it an excellent lubricant for industry applications. The viscous nature of the oil helps to stick to the gears & which in turn reduces the centrifugal force. The splash method is used to lubricant all the areas inside the gearbox. The simulation in both cases looks similar due to the adhesive nature of the oil makes it slow & proper lubrication for the gears.

                                     j) Oil contour for smaller clearance

CASE 2:

In this case, the clearance between the gears is increased & all the other parameters are the same to check the lubrication between the gears.

                                                  k) Mesh

Water Lubricant

With the increase in clearance between the gears, the water at the meshing interface is reduced this is mainly due to the availability of the fluid level is the same in both the case. The casing to be filled with 1/3rd of its height with lubricant for proper lubrication, so due to the inadequate level of lubricant the gear meshing interface left unlubricated.

                                m) Water contour for larger clearance

Oil Lubricant

                                   n) Oil contour for larger clearance

INFERENCE 

• The fluid properties used for the lubricant must have high viscous and adhesive nature to have proper lubrication which is inferred from the case 1 where oil with above fluid properties provide better lubrication for the gears.
• For larger clearance in the gears, the lubricant takes more time to lubricate the gears & also the fluid level of the lubricate is to be set according to the size of the casing.
•  The design of the casing to be altered to have a proper gear lubricant so the splashing of the gears reaches all the parts of the casing to have a proper working of the gears.