Gear Box Sloshing Effect

Gear Box Sloshing Effect

Objective:

To analyze the flow pattern of two different kinds of fluid having different properties and which will act as a lubricant over a gear of two different clearances of the same geometry, having a sloshing effect on it which can be observed using Volume of Fluid Method (VOF) in ANSYS Fluent.

Introduction:

Sloshing Dynamics: In fluid dynamics, slosh refers to the movement of liquid inside another object (which is, typically, also undergoing motion).

Gear Lubricants: Lubrication oil plays a decisive role to maintain reliable and efficient operation of gear transmissions. Gearbox lubricants are critical in maintaining efficient and effective operations. Lubricating oils must reduce wear and friction at the contact surfaces and separate them to ensure appropriate operation and avoid failures. Lubricant oil properties also affect gear dynamics, such as vibration, power characteristics, and heating. Therefore, continuously monitoring changes in lubricant properties is crucial for avoiding defects within machines and prevent unexpected breakdowns. Studies show that oil properties considerably affect gearbox behaviors and performance due to churning and sloshing.

This challenge presents the findings of a study of lubricant flow in a simple model gearbox by means of CFD (Computational Fluid Dynamics) and its validation by a series of tests on a spur gear rig. The commercial CFD code Fluent is used to simulate the splash flow of lubricant, using the techniques of dynamic meshing and VOF (Volume of Fluid). Our model considers the effects on the distribution of gear lubricant of lubricant level and physical properties as well as rotational speed. Through the case study of the sloshing effect over gear, we can see how each tooth of gear is well lubricated and also how it carry lubricant on its surface by observing the flow pattern.

ANSYS SpaceClaim 3D Model:

CASE SET-UP:

1. First, a fluid domain volume has been extracted from the above 3D model.

2. Then, in order to simplify simulation and to save time, a 2D model of inside gears has been moved into different SpaceClaim window.

3. A ‘Multiphase method’ is being used in order to define two kinds of fluid i.e. air and lubricant in fluid domain volume.

4. The air and lubricant in fluid domain region have been separated by marking the cell coordinates using the ‘Marked/Adapted Cells method’.

5. The rotation of gear is being defined by the User Define Function (UDF) file which is being inputted into ANSYS Set-up.

ANSYS Fluid Material:

Lubricant Fluid	Density (kg/m^3)	Viscosity (kg/m-s)
Water-liquid	998.2	0.001003
Oil	817	0.04006889

ANSYS Set-Up:

Model: Multiphase

Simulation Method: Volume of Fluid (VOF)

Viscous Model: K-epsilon

K-epsilon Model: Realizable-Enhanced Wall Treatment

Solver: Transient-Pressure based

Gravity = -9.81 m//s^2 (Y-direction)

User-Defined Function: To define gear motion

Remeshing Parameters:

Min. Length Scale(m) = 0.0001

Max. Length Scale(m) = 0.002

Max Cell Skewness = 0.5

Size Remeshing Interval = 5

• CASE-1 & 2

Inside Gear 2D Model:

Geometry Parameters:

Least Clearance = 0.63mm

Gear Radius = 60mm

Left Gear Centroid: X = 0mm, Y = 0mm

Right Gear Centroid: X = 115mm, Y = 0mm

Meshing Model:

Adapted/Marked Cells:

X(min) = -0.05612m	X(max) = 0.17112m
Y(min) = -0.0675m	Y(max) = -0.0375m

Solver Preference	Fluent
Relevance	100
Export Format	Standard
Sizing
Size Function	Proximity and Curvature
Relevance Center	Fine
Quality
Check Mesh Quality	Yes, Errors
Target Skewness	0.5
Smoothing	High
Inflation
Inflation Option	Smooth Transition
Transition Ratio	0.272
Maximum Layers	2
Growth Rate	1.2
Inflation Algorithm	Pre
Statistics
Nodes	51850
Elements	97678
Object Name	All Triangles Method	Body Sizing
State	Fully Defined
Scope
Scoping Method	Geometry Selection
Geometry	1 Body
Definition
Suppressed	No
Method	Triangles
Element Midsize Nodes	Use Global Setting
Type		Element Size
Element Size		5.e-004 m

Results:

• CASE-1 (Water lubricant)

Residual Plot:

Flow Pattern:

Animation Video Link: https://www.youtube.com/watch?v=Ghzq4PYBVTA&feature=youtu.be

• CASE-2 (Oil lubricant)

Residual Plot:

Flow Pattern:

Animation Video Link: https://www.youtube.com/watch?v=J6YIy5ZhlxU&feature=youtu.be

• CASE-3 & 4

Inside Gear 2D Model:

Geometry Parameters:

Least Clearance = 2.63mm

Gear Radius = 60mm

Left Gear Centroid: X = -58.5mm, Y = 0mm

Right Gear Centroid: X = 58.5mm, Y = 0mm

Meshing Model:

Adapted/Marked Cells:

X(min) = -0.0559518m	X(max) = 0.1729518m
Y(min) = -0.0685m	Y(max) = -0.0395176m

Statistics
Nodes	54222
Elements	102607

Results:

• CASE-3 (Water lubricant)

Residual Plot:

Flow pattern:

Animation Video Link: https://www.youtube.com/watch?v=UkyE2lQKRic

• CASE-4 (Oil lubricant)

Residual Plot:

Flow Pattern:

Animation Video Link: https://www.youtube.com/watch?v=3k903MvA5vY

Observations:

1. It is observed that the formation of oil lubricant film over a gear tooth is more stable than water as a lubricant on it.
2. The sloshing effect of oil is less than that of water due to its high viscosity.
3. The more the sloshing effect, the more the unstableness of lubricant on gear tooth surfaces and this results in high friction and temperature.
4. Thus, lubricants will high viscosity and less sloshing effect is more suitable for gearbox, which in this case is oil.