Gearbox Sloshing effect

The objective is to perform gear sloshing simulation on ansys fluent for two different gearboxes with different clearance. The User defined function is used which provides the angular velocity of 200rpm. Four simulations were performed:-

1. Case 1 Gearbox : Air and water
2. Case 2 Gearbox : Air and Oil
3. Case 3 Gearbox : Air and water
4. Case 4 Gearbox : Air and Oil

Geometry:-

3D model of gearbox was initially provided for this simulation. Bearing in mind of ansys academic version limitation of 512k nodes and elements and running time of transient simulation, the problem was converted into a 2D simulation. Using split body tool in spaceclaim, The 3D geometry was split in to two in midplane and the 2D surface of geometry was copied to a new design.

3D Model:-

3D cut model:-

2D model:-

In the mesh module, sizing of 0.5 mm is used for full geometry.

	CASE 1&2	CASE 3&4
NUMBER OF NODES	44776	47340
NUMBER OF ELEMENTS	84527	89858
MARKED CELLS	5376	5909

Mesh-Case 1&2:-

Mesh-Case 3&4:-

This Mesh might be useful for the first few time steps but diesn\'t play a vital role throughout the simulation. Since this simulation deals with the dyamic meshing, for each and every time step mesh will degenerate and tends to form new mesh.

Physics of Model:-

• The transient simulation was used for setup.
• Geometry is in X-Y plane, gravity is in negative Y axis.
• The volume of the fraction with two phases was used.
• K-epsilon turbulent model was used with realizable, Enhanced wall treatment method is used.
• Air and water were used for the first simulation and mamterial properties are available in Flunet database.
• Oil is used as another material with air in second and fourth simulation with properties density=887 kg/m^3 and viscosity=0.04006889 kg/ms.
• In geometry using adapt cells option, The lower region of the gearbox is marked and patched with volume of fraction - phase-2. X- and Y- coordinates are measured from space claim.
• Phase-1 is air and phase-2 is Water/air.
• A user Defined function is loaded into asys.

#include \"udf.h\"

DEFINE_CG_MOTION(right_motion, dt, vel, omega, time, dtime)
{
	vel[0] = 0.0;
	vel[1] = 0.0;
	vel[2] = 0.0;

	omega[0] = 0.0;
	omega[1] = 0.0;
	omega[2] = 2.0e2; /* [rad/s]*/
}
DEFINE_CG_MOTION(left_motion, dt, vel, omega, time, dtime)
{
	vel[0] = 0.0;
	vel[1] = 0.0;
	vel[2] = 0.0;

	omega[0] = 0.0;
	omega[1] = 0.0;
	omega[2] = -2.0e2; /* [rad/s]*/
}

• Dynamic mesh option is turned on with left and right gear linked to proper used defined function. Both left and right gear are assumed to be rigid body. Centre of gravity for left and right gear are found using space claim module.
• For dynamic Meshing, Remeshing minimum and maximum size are given as 1e-5 and 0.0025m respectively and fair skewness of 0.5.
• Even 0.005 skewness can be used but correspondingly maximum length should also be reduced. Which will increase drastically the runtime of the simulation. So based upon several iteration these values are used for all four cases.
• Velocity animation is recorded for the end of every time step and animation are shown below.
• Time step of 5e-5is used. Some other higher timesteps tend to increase the courant number which provides unstable solution of the problem.

Simulation:-

CASE 1:-

CASE 2:-

CASE 3:-

CASE 4:-

In the animation It can be noted for case 1 there is a lot of deformation in elements when the gear comes into the contact. This is due to skewness value of 0.8 provided which tends to produce poor quality mesh. But in other cases, skewness of 0.5 is used which provides decent mesh size During the siulation.