gearbox simulation

Aim- Perform the 2D simulation of the Gearbox for the given four cases and compare the result 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.

Introduction

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.

PART 1

Geometry preperation

1. Open the Ansys workbench in cross tool prompt command and open the Ansys fluent then load the given gearbox step file in fluent, extract the fluid volume.

2. Hide the housing and use supress for physics.

3. Split the body in to half to extract the 2D geometry by selection of 3D plane. Use split body command, select the body , select the x-plane then select the body which part want to remove.

4. By using ctrl+c copy the 2D geometry, paste the 2D geometry in new space claim in XY plane.

Mesh

Insert the triangle method by insert option and mesh the 2D gear with 2mm mesh size, whose nodes 10011 and elements 17089.

Setup

General

Processing -Serial

Solver -Type pressure based

Velocity formulation- Absolute

Time-Transient

2D space-Planer

Gravity- -9.81 m/s^2 y-direction

Models

Multiphase > VOF > Implict

Viscous > k-epsilon > Standard wall function

UDF

User defined code provide the information about left and right gear

#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]*/
}

User defined function > compiled > source file Add > Build > Load

Materials

Air, Engine-oil, n-heptane-liquid(c7h16)

Domain> Adapt> Refine/ course > cell Registers > new >Region

For 20%

For 30%

Dynamic Mesh

To set the left and right motion of gear and define their center use dynamic mesh setting

Left gear center- (0, 0, 0)

Right gear center (0.115,0,0)

Hybrid initialization is done and patch.

Time step size 1e-4, Max iteration/ Time step=40

Solution method-simple, Momentum - First order upwind ,Transient- First order implicit

1. 20% Immersion, Fluid - Engine oil.

https://www.youtube.com/watch?v=THFuC00rhNQ

2. 20% Immersion, fluid n -heptane

https://www.youtube.com/watch?v=THFuC00rhNQ&list=UUz-NB8CFTgd7EVF8Hz7wk1A&index=5

3. 30% Immersion, Fluid - Engine oil.

https://www.youtube.com/watch?v=Q1LS6oCF3mI

4. 30% Immersion, fluid n -heptane

https://www.youtube.com/watch?v=8lr0WB-H0EM

Result

Comparision of 20% Engine-oil and 20 % n-heptane

https://www.youtube.com/watch?v=8lr0WB-H0EM

Comparision of 30% Engine-oil and 30 % n-heptane

https://www.youtube.com/watch?v=-ZdaUJcklI8

Conclusion

The lubricant is transported by the gears from bottom to the upper portion of the gearbox as it can be observed from the simulation videos. From the results of the simulation, it can be concluded that engine-oil takes longer time to reach all the gears, unlike the n-heptane gearbox. Also, it can be observed that engine-oil with higher viscosity was not able to move quickly to all the parts of the gear with respect to n- heptane. The simulation can be extended to include other liquids with a higher viscosity to understand more clearly the effect of viscosity of the liquid to this application. Higher the fluid volume in the gear box occurs more power losses in the gear box.

Part-2

Dynamic meshing

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.

Fluid Sloshing effect

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 (UDF) is a common fixture in programming languages, and the main tool of programmers for creating applications with reusable code. Since programs are mostly composed of code that comes from the programmer, or in this case the user, most of it is composed of user-defined functions occasionally punctuated by built-in functions.

User-defined functions allow programmers to create their own routines and procedures that the computer can follow; it is the basic building block of any program and also very important for modularity and code reuse since a programmer could create a user-defined function which does a specific process and simply call it every time it is needed. Their syntax depend entirely on the programming language or application where they are created.

Though part of any programming language, user-defined functions more commonly refer to the special functions that a user creates as scripts or programs in large systems. This is because most of the functions being used in a database system or spreadsheet are built-in functions that the user simply has to call and provide parameters, and most of what the application can do is already being done by one or more built-in functions. In this case, user-defined functions are special custom functions that are meant to do something not normally done by the built-in functions. In programming languages such as C, C++ and Java almost every part of the program is user-defined, hence, these functions are no longer referred to as "user-defined" to separate them from the built-in functions, they are simply called functions.

In CFD

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

UDFs are written in the C programming language using any text editor and the source code file is saved with a .c extension (e.g., myudf.c). One source file can contain a single UDF or multiple UDFs, and we can define multiple source files.

UDFs are defined using DEFINE macros provided by ANSYS FLUENT. They are coded using additional macros and functions also supplied by ANSYS FLUENT that access ANSYS FLUENT solver data and perform other tasks.

Every UDF must contain the udf.h file inclusion directive ( #include "udf.h") at the beginning of the source code file, which allows definitions of DEFINE macros and other ANSYS FLUENT-provided macros and functions to be included during the compilation process. Values that are passed to a solver by a UDF or returned by the solver to a UDF are specified in SI units.

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 will collapsed and negative volume cell detected will occurs to avoid this use the remeshing and reduce the time step.