Simulation of Sloshing effect in Gearbox using Ansys fluent

Objective: Perform Simulation of Sloshing effect in Gearbox using Ansys fluent and write a detailed report explaining the results obtained.

Question:

For this challenge, you have to perform the four simulations in the Gearbox and then you have to compare the results among all the four cases.

Part 1:

1. 20% Immersion, Fluid - Engine oil.
2. 30% Immersion, Fluid- Engine oil.
3. 20% Immersion,Fluid-n-heptane (c7h16).
4. 30% Immersion,Fluid-n-heptane (c7h16).

Part 2:

1. What is Dynamic meshing? Give some other examples where dynamic meshing can be used.
2. What is the fluid Sloshing effect? Discuss whether the sloshing effect is good or bad? Explain.
3. What is the use of UDF?
4. Discuss the common errors that occurred in the simulation. A] 'Dynamic mesh failed' error. B] 'Negative cell volume detected' error.

What is Dynamic meshing? Give some other examples where dynamic meshing can be used.

Dynamic meshing refers to situations in which the computational grid changes dynamically during the run of the CFD simulation. This opens up for the possibility to simulate flows where the geometry changes with time, e.g. flows around falling objects or internal combustion in cylinders.

In ANSYS Fluent the dynamic mesh capability is used to simulate problems with boundary motion, such as check valves and store separations. The building blocks for dynamic mesh capabilities within ANSYS Fluent are three dynamic mesh schemes, namely, smoothing, layering, and remeshing. A combination of these three schemes is used to tackle the most challenging dynamic mesh problems. However, for simple dynamic mesh problems involving linear boundary motion, the layering scheme is often sufficient. For example, flow around a check valve can be simulated using only the layering scheme.

The dynamic mesh model can be used to model flows where the shape of the domain is changing with time due to motion on the domain boundaries. Combined with the six degrees of freedom (6 DOF) solver, dynamic mesh allows the trajectory of a moving object to be determined by the aero or hydrodynamic forces from the surrounding flow field. Overset meshing allows complex geometrical problems to be decomposed into a system of geometricallysimpler overlapping meshes. Overset and dynamic meshing can be applied to a wide variety of applications, from automotive and aerospace to chemical and environment industries.

What is the fluid Sloshing effect? Discuss whether the sloshing effect is good or bad? Explain.

In fluid dynamics, slosh refers to the movement of the free surface of the liquid inside another object which is undergoing motion. Important examples include propellent slosh in spacecraft, ships, and trucks transporting liquids.

A similar effect is observed in a gearbox. Inside a gearbox, the gears are partially immersed in a lubricant and the lubricant is transported by the gear motion so that the lubricant reaches all the teeth of the gear. This brief report is based on the numerical simulation conducted to visualize the movement of lubricant inside a gearbox.

Sloshing of liquid in the storage tank may result in negative effects such as deformation and failure of tank walls due to impact. If an open tank is subjected to ground motions, sloshing may lead to liquid spillage. Therefore, sufficient clearance need to provide between the free surface and top of the tank or roof must be provided.

Anti-slosh devices such as baffles are widely used in order to limit the adverse liquid slosh effect on directional performance and stability of the tank vehicles.

What is the use of UDF?

A user-defined function, or UDF, is a function that you program that can be dynamically loaded with the ANSYS FLUENT solver to enhance the standard features of the code. For example, you can use a UDF to define your own boundary conditions, material properties, and source terms for your flow regime, as well as specify customized model parameters (e.g., DPM, multiphase models), initialize a solution, or enhance postprocessing.

A UDF is basically a C program or a C function that can be dynamically loaded with ANSYS FLUENT to enhance its standard features. The features of a typical UDF are as follows :

Discuss the common errors that occurred in the simulation. A] 'Dynamic mesh failed' error. B] 'Negative cell volume detected' error.

Dynamic mesh failed' error

Dynamic meshing failed refers to situations in which the computational grid changes dynamically during the run of the CFD simulation. This opens up for the possibility to simulate flows where the geometry changes with time.

Negative cell volume detected' error

Negative cell volume detected will occurs when meshed cell moved too far in one timestep so the cell gets collapsed and negative volume cell detected will occurs to avoid this. Use the remeshing and reduce the time step to overcome this.

Case Setup and Execution:

Geometry:

Geometry is imported to Ansys Space Claim.

Volume is extracted using Volume Extract option.

The 2D geometry is created using split body option > choose the midplane > extracted volume > then select the faces to be removed, create a section view & copy-paste the section view in a new file.

Named Selections:

Meshing: All Triangles Method

Element size: 35mm

Nodes: 8469

Elements: 14302

Setup:

Solver Time:Transient state

Type: Pressure based

Gravity: -9.81m/s2 in Y axis

Multi-Phase Model: Volume Of Fluid

No. of eulerian phases - 2

Formulation - Implicit

Viscous model: k-epsilon with realizable & enhanced wall treatment

Materials:

Air:

• Density:1.225 kg/m^3
• Viscosity:0.000017894 kg/m-sec

Engine Oil:

• Density:889 kg/m^3
• Viscosity:1.06 kg/m-sec

n-heptane-liquid:

• Density:684 kg/m^3
• Viscosity:0.000409 kg/m-sec

Phases:

• Primary phase:Air
• Secondary phase: Engine Oil/n-heptane-liquid

User defined function:

• Udf file :rate.c
• For the rotation of the gear we need to build the udf file and load into the fluent.
• Below shows the 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]*/
}

Dynamic Meshing:

• Zone Name:Left gear
• Type :Rigid body
• Centre of gravity=(0,0) mm
• Zone Name:Right gear
• Type :Rigid body
• Centre of gravity=(115,0) mm

Remeshing details:

Region Register:

20% Immersion

• Type:quad
• Location:inside
• start point:(-0.0675,-0.0675,0)
• End point:(0.1825,-0.0405,0)

30% Immersion

• Type:quad
• Location:inside
• start point:(-0.0675,-0.0675,0)
• End point:(0.1825,-0.027,0)

Initialization:

• We need to initialize the hydrid initialization scheme
• After initialization we need to patch the file
• phase:Engine Oil/n-heptane-liquid
• Volume fraction value=1

Time step and Time step size:

• Time step size=5.56e-6
• Number of Time steps=5000
• Max iterations /Time step=40

CASE-1: 20% Immersion, Fluid - Engine oil.

Residuals:

Volume Fraction Contour:

Volume Fraction Animation:

CASE-2: 30% Immersion, Fluid - Engine oil.

Residuals:

Volume Fraction Contour:

Volume Fraction Animation:

CASE-3: 20% Immersion, Fluid-n-heptane (c7h16).

Residuals:

Volume Fraction Contour:

Volume Fraction Animation:

CASE-4: 30% Immersion, Fluid-n-heptane (c7h16).

Residuals:

Volume Fraction Contour:

Volume Fraction Animation:

Conclusion:

• 30 % immersion of n-heptane liquid & engine oil is heplful for lubrication of all teeth due to higher immersion.

• In case of n-heptane liquid there is higher sloshing effect due to lower viscosity.

• Sloshing effect in case of engine oil is less compare with n-heptane liquid due to higher viscosity.

• 30 % immersion Engine oil is best combination for proper lubrication of oil in all teeth & also good temprature distribution due to higher viscosity.

• It is observed that n-heptane liquid does not properly lubricate compare with engine oil due to lower visocity & its cannot stickup with gear for long time.