Gearbox Sloshing Effect

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.

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).

Gearbox:

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, name itself defines what it is — a box containing gears. In the most basic sense, a gearbox functions like any system of gears, a 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 gearsto worrngears and others such as planetary gears. The gears are used on which are supported by and rotated via rolling element bearings. The gearbox is a mechanical method of transfering 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 .

Lubrication:

Lubrication is the process or technique of using a lubricant to reduce friction anti wear and tear in a contact between two surfaces.

Lubricants can be solids (such as Molybdenum disulfide MoS2), solid/liquid dispersions (such as grease), liquids (such as oil or water), liquid/liquid dispersions or gases. Fluid-luibricated systems are designed so that the applied load is partially or completely carried by hydrodynamic or hydrostatic pressure, which reduces solid body interactions (and consequently friction and wear).

Depending on the degree of surface separation different lubrication regimes can he distinguished.

Adequate lubrication allows smooth, continuos operation of machine elements, reduces the rate of wear, and prevents excessive stresses or seizures at bearings. When lubrication breaks down components can rub destructively against each other, causing heal local welding, destructive damage and failure.

Methods of Lubrication:

Lubrication is essential to the proper functioning of an industrial gearbox. Adequate levels of lubrication benifit a gearbox by lubricating the teeth and rernoving heat generation from operations. Lubricant is also used on the various hearings inside the gearbox. Adequately lubricating these elements of industrial gearbox will result in mechanical efficiency, reliability, low rnairftenanco and a long equipment span.

Grease Lublication:

Grease lubrication can be used for industrial gearbox systems,that are open or closed, as long as they run at low speeds. The grease must have thecorrect viscosity with good fluidity, especially when used in an enclosed unit. Grease lubrication should not be used for continuous operation or high load gear drives. It should also be noted that grease lubrication has no cooling effect. A sufficient amount of grease must be used to ensure gear teeth are lubricated, but excess grease can result in power losses and viscous drag.

Splash Lubrication:

Helical, spur, and bevel gearboxes are typically lubricated using splash lubrication. During splash lubrication the gears or another components within the gearbox dip into an oil bath. Through rotation these components begin 'splashing' the oil necessary chambers and crevices, that may contain additional gears or hearings in need of lubricant. Provisions must be made to ensure the gear teeth are not fully immersed in the bath. If teeth are immersed in oil, emessive losses will result due to the oil being churned.

Spray Lubrication:

High speed industrial gearboxes are lubricated through spray lubrication. These units often have spray lubrication provided through the use of nozzles, with oil circulating at a pressure of 0.7 bar. Extra care must he taken to ensure the oil reaches the contacting surfaces. This process can become difficult as centrifugal forces deflects the stream of oil.

Forced oil lubrication:

Forced oil lubrication is preferred for high speed applications, and includes methods such as oil mist, oil spray, and oil drop. In the oil mist method, oil is atomized so that saturates all areas of the gears and other internal components. In contrast , the oil spray method applies oil lubricant directly to the gears and other components, but this method is not always effective, as high centrifugal forces affect the direction of the oil spray.
The oil drop method pumps, or 'drops'; oil directly onto the surfaces where it's needed. A pump takes lubrication from a reservoir and delivers it to the gears and/or bearings via an internal piping system. This method can often be found in conjunction with the splash (aka oil bath) method, where some components may be difficult to reach via oil splash.

Gearbox sloshing effect:

ANSYS WORKBENCH is to be open by visual c++ and from there ANSYS FLUENT is selected.

Geometry:

Fluid volume is extracted by selecting outer circle four edges. Then extracting fluid volume model along xy plane splitted in two ways so that internal gears can be seen easily.

Outer 2D face is copied and pasted in new design . Analysis is done on 2D surface

Meshing and Name selection:

Model is mesh with element size of 0.75 mm . Whole face of Left and Right gear is selected to name selection of it individually to their respective gear.

Model setup:

• Solver - Pressure based
• Transient state
• Gravity along negative y direction
• Turbulence model- K epsillon>Realizabel>Enhanced Wall heat treatment
• Material- Air , Engine oil , n-heptane
• Mutliphase model ON > Volume of fraction > No. of eulerian phases-2> Formulation> Implicit(As with explicit courant number value crosses which leads to solution failure)
• Phases - Primary(Air) , Secondary(Engine oil for first case and n-heptane for second case)
• Defining Fluid region in cell register>new > Giving co-ordinates for 20% and 30% immersion of lubricant of total geometry. This fluid region will ensure lubricant reaching to all gears.
• Compling User defined function file in User defined function which will help in rotation of both left and right gear
• Dynamic Mesh- This helps in simulating the model flows where the shape of the domain changes with respect to time due to motion of domain boundaries.

For gear sloshing simulation , the motion of gears are given UDF which states rotation of gears at 200 rad/sec

The dynamic mesh works on three different functions:

• Smoothing- The nodes move according to boundary motion and elements are stretched like springs to keep nodes joined.
• Layering- Mesh moves layer by layer(useful in sliding mesh for less magnitude deformation).
• Remeshing - Helps in overcoming negative volume cell error occuring during mesh. The mesh is remeshed locally in regions that do not satisfies user specific limit on sizes and skewness

Dynamic mesh zone is created for each left and right gear. For left gear center of gravity is at 0 where as for right gear it is located at 115 mm as checked in spaceclaim

• Initialization- hybrid
• Patch -for first case phase>engine oil > volume fraction value 1 and for second case phase n-heptane> volume fraction value 1

Calculation of Time step size and no. of steps:

Each gear is having 23 teeth and making it rotate for more than 3 rotation due to limitations.

We know that ω=2πN60">ω=2πN60ω=2πN60

ω=200(radsec)">ω=200(radsec)ω=200(radsec)

S0 , N = 6000/π">ππ = 31.831 rps

So , Time required for one rotaion is 1/31.831 = 0.03141 sec

Total number of teeths = 46

So , Time required for rotation of each teeth = 0.03141/46 = 0.0006828

Dividing 1 teeth by 10 division for reasonable accuracy we get 0.0006828/10 = 6.828e-5 sec

Assuming round-off time step size to be 5e-5 sec

Total time required for 3 rotations of gear is 3 * 0.03141= 0.09423

Total number of timestep = 0.09423/5e-5 = 1884.6 = 1900.

Solution:

Case (a) 20% immersion Engine oil:

3 rotation complete:

We can see that the flow time has crossed 0.09423 which is value for 3 rotation.

Residual:

Contour:

Animation:

At the starting time when gears are in idle or at rest condition i.e t = 0 sec the lubrication fluid engine-oil is concentrated at the bottom of the gearbox in defined 20%fluid region, In case of 20%fluid region, and no. of gear teeth already dipped in the engine oil are very less, splashing of lubricant helps to spread the lubricant on all over parts but, the splashed oil from walls sliding down at the bottom is less hence when gears start rotating then minimum no. of teeth will carry lubricant with it . Due to this gears are operated in a loss-of-lubrication operating condition for a long time, their heat dissipation performance would detoriate which result in a drastic increase in tooth temperature, which may lead to scuffing failure.

Case (b) 30% immersion Engine oil:

3 rotation complete:

We can see that the flow time has crossed 0.09423 which is value for 3 rotation.

Residual:

Contour:

Animation:

At the starting time when gears are in idle mat rest condition i.e t = 0 sec the lubrication fluid engine-oil is concentrated at the bottom of the gearbox in defined 30%fluid region. In case of 30%fluid region, significant no. of gear teeth are already dipped in the engine oil, this configuration has enough lubrication to fill the gap between gear teeth right from first rotation of the gear. Splashing of lubricant helps to spread the lubricant on all over parts and is more effective, the splashed oil from walls sliding down at the bottom is more as compared to 20% configuration. In this case gears are operated with adequate lubrication condition for a long time and hence reduces the effect of problems which were associated with loss-of-lubrication operating condition.

Case (c) 20% immersion n-heptane oil:

3 rotation complete:

We can see that the flow time has crossed 0.09423 which is value for 3 rotation.

Residual:

Contour:

Animation:

At the starting time when gears are in idle or at rest condition i.e t= 0 sec the lubrication fluid- n-heptane liquid is concentrated at the bottom of the gearbox in defined 20% fluid region. In case of 20% fluid region and no. of gear teeth already dipped in the n-heptane liquid are very less, splashing of lubricant helps to spread the lubricant on all over parts but, the splashed oil from walls sliding down at the bottom is less hence when gears start rotating then minimum no, of teeth will carry lubricant with and more consumption as viscosity of n-heptane liquid is low though low ability to stick tooth surface. Gears are operated in a loss-of-lubrication operating condition for a long time, their heat dissipation performance would detoriate which result in a drastic increase in tooth temperature, which may lead to scuffing failure and other associated failures.

Case (d) 30% immersion n-heptane oil:

3 rotation complete:

We can see that the flow time has crossed 0.09423 which is value for 3 rotation.

Residual:

Contour:

Animation:

At the starting time when gears are in idle or at rest condition i.e t = 0 sec the lubrication fluid n-heptan-liquid is concentrated at the bottom of the gearbox in defined 30% fluid region. In ease of 30% fluid region, significant no. of gear teeth are already dipped in the n-heptane-liquid, this configuration has enough lubrication to fill up the gap between gear teeth right from first rotation of the gear but its low viscocity reduces ability to stick to gear tooth surface. Splashing of lubricant helps to spread the lubricant on all over pans and is more effective, the splashed oil from walls sliding down at the bottom is more as compared to 20% configuration. In this case gears are operated with adequate lubrication condition for a long time and hence reduces the effect of problems which were associated with loss-of lubrication operating condition. But the low viscosity is matter of concern for using n-heptane-liquid for lubrication in gearbox .

Conclusion:

Simulation of gearbox gear with 'Four' different configurations- in combination with Two' different lubricants 'engine-oil and n-heptane-liquid' and Two' different lubrication region 20% and 30%.

At beginning i.e time t=0 sec, all lubricate is concentrated bottom of a gearbox 30% immersion has more lubricant than that of 20% immersion case. When gear stags rotating there is enough lubrication to fill We gap between teeth, right from first rotation of the gear in 30% immersion case. Whereas, the gears are in a loss of-lubrication operating condition for a long time due to less lubricant in 20%immersion case. Though splashing of lubricant helps to spread the lubricant on all over nags in both 20% 30% immersion cases .30% immersion is more effective. Engine oil holds more benefits while operating at higher temperature as viscocity of engine oil = 1.06 kg/(m-s) is more than viscocity of n-heptane-liquid = 0.000409 kg/(m-s) Engine-oil has more ability to stick to the tooth surface as compared to n-heptane-liquid this is because engine-oil has high viscosity that results in appropriate temperature distribution. The higher value of engine-oil viscosity results in lower oil consumption and less wear during gear rotation.

01. What is dynamic meshing and where .e dynamic meshing useful? Give other examples and describe the advantage and disadvantages of dynamic meshing.
Dynamic Meshing:-

Dynamic Mesh Module is a tool that allows the motion of parts (or subparts) relative to static one, which therefore makes the fluid volume changing in time frame In dynamic mesh model the boundaries of a cell zone are allowed to move relative to other boundaries of the zone, and to adjust the mesh accordingly. The bourtaries can move rigidly with respect to each other (that is, linear or rotational motion), and/or deform
The motion of the boundaries can be:

1. Rigid - Pistons moving inside an engine cylinder or a flap deflecting on an aircraft wing.

2. Deforming - The elastic wall of a balloon during inflation or a flexible artery wall responding to the pressure pulse from the heart.

In either case, the nodes that define the cells in the domain must he updated as a function of time, and hence the dynamic mesh solutions are inherently unsteady.

An important special case of dynamic mesh motion is called the sliding mesh in whi. all of the boundaries and the cells of a given mesh zone move together in a rigid body motion. In ths situation, the nodes of the mesh move in space (relative to the fixed, global coordinates), but the cells defined by the nodes do not deform.

The mesh Smoothing and Remeshing techniques, provide instant mesh deformation capability. Remeshing is used when the mesh is more sensitive to mesh changes, which can be used to manually specify ranges of maximum and minimum elements in the Maximum and Minimum Length Scale for mesh changes.

In. Dynamic Mesh Zone section, areas or boundaries of the model that should be affected byt he mesh change must be defined, such as by Deforming to change the boundaries in the area (fluid around a moving object or a boundary-changing object), Rigid Body to moving physical boundary and moving boundaries but not boundaries themselves, from Stationary to fixed body and finally from System Coupling to FSI solution.

Generally, the dynamic mesh technique is used when simulating models that require a moving mesh area. Whenever the problem model was such that the fluid zone required mesh moment changes over time, the Dynamic Mesh technique will be used.

The dynamic meshing can be used to model flows whom.-

1. The shape of the domain is changing with time due to motion on the domain boundaries.

2. Six DOF dynamic mesh for modelling variation of location and angle of ship and boat in wavy sea situation.

3. Simulation of the tidal turbine using six DOF dynamic mesh method (calculating rotation speed).

4. Releasing of food box from airplane using six DOF dynamic method.

5. Simulation of globe valve movement during the time.

6. Train movement in the tunnel by variable velocity function in a urban tunnel.

7. Simulation of flap movement of an airplane wing.

8. Modelling the underwater vehicle in Submerged and nonsubmerged situation.

9. Solid fuel combustion and modelling solid height level during burning fuel.

10. Fluid solid interaction of blood flow and vessel.

11. FSI simulation blood flow pumping in human heart.

12. Fluid solid interaction of airflow around building and final deflection and fluctuation (two way and one way FSI)

13. Two and fourstroke internal combustion engine.

14. Automotive piston moving.

15. Gearbox.

Advantages :

1. This model enables the spatial variation of the defined areas for fluid flow and allows the mesh of the region at the same time as the spatial location of the points and boundaries of the region changes compatibility with the place at the present moment.

2. Boundaries or motion of objects can be moved based on in-cylinder motion (11PNI, stroke length, crank angle,e1c), Prescribed motion via profiles or UDF, Coupled motion based on hydrodynamic forces from the flow solution, via FLUENT's 6 DOF model.

3. The dynamic mesh model can he applied to single or multiphase flows (and multi-species flows).

Disadvantage :

Inaccurate rerneshing settings under dynamic mesh may lead to error - update dynamic mesh tailed. Negative cell volume detected. and Floating point exception error. This may hap, because remeshing may be too coarse.

Q2. What is sloshing and explain whether the sloshing effect is good or bad for any applications?

In fluid dynamics, sloshing refers to the mmement of liquid inside another object (which is, typically, also undergoing motion). The liquid must have a free surface to constitute a slosh dynamics problem, where the dynamics of the liquid can interact with the container to alter the system dynamics significantly.

For example propellant slosh in spacecraft -tanks and rockets (especially upper stages), and the free surface effect (cargo slosh) in ships and trucks transporting liquids (for example oil and gasoline). However, it has become common to refer to liquid motion in a completely filled tank, i.e. without a free surface, as "fuel slosh".

Such motion is characterized by "Inertial waves" and can be an important effect in spinning spacecraft dynamics. Extensive mathematical and empirical relationships have been derived to describe liquid slosh. These types of analyses are typically undegaken using computational fluid dynamics and finite element methods to solve teh fluid structure interaction problem , especially if the solid container is flexible. Relevant fluid dynamics non-dimensional parameters include the Bond number , the Weber number, and the Reynolds number.

Slosh is an important effect for spacecraft ships, and some aircraft. Slosh was a factor in the Falcon 1 second test flight anomaly and has been implicated in various ,her spacecraft anomalies including a near-disaster with the Near Earth Asteroid Rendezvous (NEAR Shoemaker) satellite.

Sloshing is also a period, motion of the free surface of the liquid in a partially filled lank or container that can be caused by smeral factors. It is viewed in many applications. In freely slosh it can produce forces that came instability, rollover, and failure or damage in tank or container in some cases. Baffles used as sloshing suppression devices. The severity of sloshing and its dynamic pressure loads depend on the tank geometry, the depth of the liquid, the amplitude and the nature of the tank motions. They also depend on the frequency of excitation over a range, frequencies close to the natural frequency of the fluid.

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.

Liquid sloshing strongly influences the directional dynamics and safety performance of highway tank vehicles in a highly adverse manner.

Hydrodynamic forces and moments arising from liquid cargo oscillations in the tank under steering and/or braking maneuvers reduce the stability limit and controllability of partially-filled tank vehicles.

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

Sloshing or shifting cargo, water ballast, or other liquid (e.g., from leaks or fire fighting) can cause disastrous capsizing in ships due to free surface effect this can also affect trucks and aircraft.

The effect of slosh is used to limit the bounce of a roller hockey ball. Water slosh can significantly reduce the rebound height of a ball but some amounts of liquid seem to lead to a resonance effect Many of the balls for roller hockey commonly available contain water to reduce the bounce height,.

Q3. What is UDE, Explain the usage of UDE ?

A userdefined 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 campused of user-defined functions occasionally punctuated by built-in functions.

Userdefined 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 userdefined 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, userdefined 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, userdefined functions are special custom functions that are meant to do something not normally done by 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 userdefined 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 terns for flow regime, as well as specify customized model pararneters (e.g., DPM, multiphase models), initialize a solution, or enhance postprocessing.

UDFs are written in the C programming language using any tort editor and the source code file is saved with a .c extension (e.g., nyucif .0. One *muffle can contain a single UPF or multiple UPFs, and we can define multiple source files.

UDFs are defined using DEFINE macros provided by ANSVS 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 relumed *the solver to a UDF are specified in SI units.

UDF file used for this challenge is:

Source files containing UDFs can be either interpreted or compiled in ANSYS FLUENT. For interpreted UDFs, source files are interpreted and loaded directly at runtime in a single-step process. For compiled UDFs the process involves two separate steps. A shared object code library is first built and then it is loaded into ANSYS FLUENT.

UDFs allows to customize ANSYS FLUENT to fit particular modeling needs. UDFs can be used for a variety of applications. Some examples include

customization of boundary conditions, material property definitions, surface and volume reaction rates, source terms in ANSYS FLUENT-transport equations, source terms in user-defined scalar (UDS) transport equations, diffusivity functons, etc.

adjustment of computed values on a once-per-iteration basis

initialization of a solution

asynchronous (on demand) execution of a UDF

execution at the end of an Iteration, upon exit from ANSYS FLUENT, or upon loading of a compiled UDF library

postprocessing enhancement enhancement of existing ANSYS FLUENT models (e.g., discrete phase model, multiphase mixture model, discrete ordinates radiation model)

Q4. Discuss the common errors that occurred in the simulation. A] 'Dynamic mesh failed' error. B] 'Negative cell volume detected' error.

Dynamic mesh failed error,

Negative cell volume detected:

Negative cell volume usually means that the mesh moved too far in a single time step so that the cells have collapsed. In other words, the remeshing done by the Fluent in the dynamic zone is too coarse and the distance moved per time step may be greater than the edge or cell size in the dynamic region. Reducing the size of the timestep usually solves this problem. In this simulation, this error was solved by reducing the time step size to 5e-05 and selling the minimum length scale to 0.5 mm and maximum length scale. 1.5 mm. This solved the problem as both are below the mesh size of 0.75 mm for the triangular elements.

Floating-point exception:

It simply means that the solver has encountered an arithmatic operation that it can not compute. For example division by zero or a mathematical expression for which the obtained solution is out of defined range. Out of many reasons behind this error, one of the basic causes is zero in the initial conditions like zero turbulent K.E., Zero temperature, zero pressure in a compressible flow problem, etc. Usually to solve it in one of the following remedies work,

Limit the time step size, Reduction of the under relaxation factor- Its a technique that enables the replacement of values during the solution to be done based on the weighted average between the old and the new values. An under-relaxation factor of 1 means that the old values were totally replaced with the new set of values obtained at the end of the current iteration. Whereas an under-relaxation of 0 means completely ignoring the new results and carrying forward with the old values. Generally, values between 0 and l are used to stabilize the convergence process. The suggested values are 0.7 for velocity and 0.3 for pressure and other scalar fields. Changing pressure value to 0.1 and momentum to 0.3 helps in overcoming floating-point exception error.

Selection of correct solver settings: Implicit Vs explicit scheme in VOF: In VOF methods, explicit is simply an interface tracking scheme. It sees the interface at time( obtains the momentum at that point ten extrapolates to get a confinuous interface at time t+1. Whereas the implicit scheme actually calculates the interface location by making use of the volume fraction equation. The implicit scheme is somficattly more stable and hence bigger time step sizes can be used.

Failure to load Me UDF: Sometimes the Fluent fails to load the UDF from the file. This can be solved by launching the workbench from the command prompt of Microsoft Visual C++ for windows.