GEARBOX SLOSHING EFFECT

INTRODUCTION

• A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces. The property of reducing friction is known as lubricity.
• The most basic definition of a gearbox is that it is a contained gear train, or a mechanical unit or component consisting of a series of integrated gears within a housing. In fact, the name itself defines what it is; a box containing gears. In the most basic sense, a gearbox functions like any system of gears; it alters torque and speed between a driving device like a motor and a load.
• The gears inside of a gearbox can be any one of a number of types from bevel gears and spiral bevel gears to wormgears and others such as planetary gears. The gears are mounted on shafts, which are supported by and rotate via rolling element bearings. The gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed.
• Gearboxes are used in many applications including machine tools, industrial equipment, conveyors, and really any rotary motion power transmission application that requires changes to torque and speed requirements.

CASE DESCRIPTION

• Low clearance gearbox with water as a lubricant.
• Low clearance gearbox with oil as a lubricant.
• High clearance gearbox with water as a lubricant.
• High clearance gearbox with oil as a lubricant.

LUBRICANT PROPERTIES

GEOMETRY

1. SOLID MODEL

2. FLUID VOLUME

3. 2D PLANE EXTRACTION OF THE FLUID VOLUME FOR LOW CLEARANCE GEAR

4. 2D PLANE EXTRACTION OF THE FLUID VOLUME FOR HIGH CLEARANCE GEAR

MESHING

SIMULATION SETUP

1. A double-precision model is utilized, and the problem is solved iteratively using 4 parallel processors.
2. Solver: 2D Transient-State, Pressure-Based solver with gravity enables as -9.81 m/s² in Y.
3. Turbulence Model: k-epsilon with Enhanced Wall Functions
4. A multiphase VOF model is enabled to separately model the air and the corresponding lubricant.
5. The VOF model consists of 2 Eulerian phases with implicit formulation.

         Primary Phase: Air

         Secondary Phase: Corresponding lubricant

1. Gears are rotating at an angular velocity of 200 rad/s. This is made possible with the help of an UDF (User Defined Function). Left gear has clockwise whereas the right gear has anti-clockwise motion. 
2. As it’s a moving geometry simulation, mesh will deform due to gear motion with each time step. To avoid this, dynamic meshing is enabled.

1. Method of Initialization: Hybrid
2. Patching

1. Simulation is run for 5 revolutions. This implies a total of 0.159 seconds. Time step size chosen is 0.0001 seconds.

                  Time for 1 revolution = `(2*pi)/omega` = 0.0314 sec

UDF CODE

#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]*/
}

RESULTS

1. RESIDUALS

1.1. LOW CLEARANCE GEAR WITH WATER AS LUBRICANT

1.2. LOW CLEARANCE GEAR WITH OIL AS LUBRICANT

1.3. HIGH CLEARANCE GEAR WITH WATER AS LUBRICANT

1.4. HIGH CLEARANCE GEAR WITH OIL AS LUBRICANT

2. ANIMATIONS

2.1. LOW CLEARANCE GEAR WITH WATER AS LUBRICANT

2.2. LOW CLEARANCE GEAR WITH OIL AS LUBRICANT

2.3. HIGH CLEARANCE GEAR WITH WATER AS LUBRICANT

2.4. HIGH CLEARANCE GEAR WITH OIL AS LUBRICANT

CONCLUSIONS

• Both oil and water can work as a proper lubricant for this case as all the teeth of the gears are covered in the lubricant throughout their revolution.
• There is little sloshing with oil in the top half of the gearbox than water due to its higher viscosity and the tendency of oil particles to stick together.
• the splashing in the top half of the gearbox where the lubricant completes one rotation is lesser for the high clearance model as there is more space for the lubricant to pass through.