Gearbox Sloshing Effect.
Gearbox Sloshing Effect
Aim: To perform simulation with two different fluids in the gearbox and comparing the results among the cases.
Objective: To perform four different simulations(cases) with two different fluids.
- 20% Immersion, Fluid - Engine oil.
- 30% Immersion, Fluid- Engine oil.
- 20% Immersion,Fluid-n-heptane (c7h16).
- 30% Immersion,Fluid-n-heptane (c7h16).
Description:
A gear box is a mechanical method of transferring energy or motion from one device to another and is used to increase torque while reducing speed. Automotive gearboxes are used to reduce load on th engine by manipulating torque and speed. They have an option to select one of several different gear ratios.Gear box varies the leverage between the engine and the driving wheels. Once the engine has reached a number of revolutions per minute, it is advisible to increase the gear to reduce the engine rpm to reduce wear on the engine, allow more control, greater speeds,better accelerationand a better fuel economy.Most gearboxes are used to increase torque and reduce the speed of a output shaft. This produces a mechanical advantage. The automotive gearbox also have the provision to provide an increase in outputshaft speed with reduction of torque. The most basic type of gear is a spur gear , and it has straight cut teeth where the teeth cut parallel to the axis of the gear. Depending on the size of the vehicles , the size of gears also varies. It permits engine crankshaft to revolve at high speeds, while the wheels turns at slower speeds.
Gear boxes rely on lubrication to reduce friction and provide cooling for optimal operationand life. There are several methods for lubricating a gearbox, with mostcommon being grease lubrication , oil splash and forced oil lubrication.
- Oil Splash lubrication - Mostly used for helical, spur and bevel gearboxes. This method is refered as an oil bath, because it uses a reservoir is filled with oil. As the gears rotate , they dip into the oil bath and splash the oil on to the other gears. The effectiveness of oil splash lubrication is heavely depedent on the speed of the gears.
- Forced Oil lubrication - Generally prefered for high speed applications and includes methods such as oil mist, oil spray and oil dip. The oil spray method applies oil lubricant diretly to gears and other components but this method is not always effective. The oil drop method pumps or drops oil directly onto surfaces where its required. From reservoir directly delivers it to gears by means of a piping system.
Regardless of lubrication method used, the right type of lubrication is critical to gearbox performance. Also parameters involved in selecting a lubricant , viscosity is important.
Procedure:
Geometry: (Converting 3D model to a 2D model)
- Importing geometry to SpaceClaim:-
- Extracting Fluid Volume:-
- Geometry obtained after splitting body:-
- Required 2D geometry:-
Meshing:
Mesh considerations :
- Element size - 0.001m.
- Number of cells across gap -1.
- Number of Nodes - 15875.
- Number of Elements - 28327.
- Capture proximity - Yes.
Setting up the simulation:
- After meshing the geometry, close the meshing window and open the SETUP. Initiall check if the complete geometry is imported or not.
- In Setup > go to Physics > Models > select Viscous model > select model=K-epsilon - standard, Near wall treatment=standard wall function > click Ok.
- Select General > choose Solver Type= Pressure Based, Time=Transient > next unable Gravity > set Gravitational Acceleration i.e. x= 0 m/s^2, y=-9.81 m/s^2 and z=0.
- Now go to Materials > select Material type=Fluid, for selecting multiple materials click on Fluent Database > select Engine oil & n-heptane(c7h16) > select Copy > click on Close. Then the selected materials appear in the Fluent Fluid Materials. If required rename the selected fluids. Materials for different cases are:
case-1 Air - 20% Immersion, Fluid - Engine oil.
case-2 Air - 30% Immersion, Fluid - Engine oil.
case-3 Air - 20% Immersion,Fluid-n-heptane (c7h16).
Case-4 Air - 30% Immersion,Fluid-n-heptane (c7h16).
Change the materials as per the case we want to run by changing the cell registers as per the percentage of immersion.
- In Models > Multiphase model > select Model=Volume of Fluid, volume fraction parameters=Implicit and Number of Eulerian Phases=2 > click Apply.
- For defining the fluid region go to Domain > Adapt > select Refinement Criterion/Coarsening Criterion > select Cell Registers > go to New > Region > enter the Input Coordinates ( To find coordinates go to Spaceclaim) initially it will be named as Region > select Save/Display or Save. To check the properties go to Cell Registers > Manage > select particular Region that is created > check them in Properties. i.e.
(a) Cell Registers for 20% Immersion-
Region- X-min = -0.054m. X-max = 0.169m.
Y-min = -0.0675m. Y-max = -0.0405m.
(b) Cell Registers for 20% Immersion-
Region- X-min = -0.06186m. X-max = 0.18m.
Y-min = -0.0675m. Y-max = -0.027m.
- After setting the Regions, go to User Defined > select Functions > go to compiled > then Compiled UDF's window pops up > in Source Files select Add > redirect and select the UDF file (rate.c) > click Ok > then select the rate.c in Source Files and initially click on Build to create the Library > check if it is created or no in console > then click on Load.
User Designed Function file -
Time Calculation:
> Angular Velocity=200 rad/sec
> ω=(2πN)/60.
> N=1910.82
> RPS=31.84
> Time required for one rotation=1/(31.84)=0.0314sec.
- Again go back to Domain > Mesh Models > select Dynamic Mesh > here select Smoothing, Remeshing > then click on settings in Dynamic Mesh > in Smoothing select Spring/Laplace/Boundary Layer > now go to Remeshing > select Remeshing Methods and sizing options = Local Cell > next in Parameters select Minimum Length Scale=0m, Maximum Length Scale=0.0018m, Maximum Cell Skewness = 0.5, Size Remeshing Interval = 2 > To check the values go to Mesh Scale Info.
- After setting the values, in Dynamic Mesh > go to Dynamic Zones > we can find two zones are created i.e. left_gear- Rigid Body and right_gear- Rigid Body.
- To check the motion of both the gears, select the Display Zone Motion. Before the Preview in the Zone Motion, following Time Control settings are done as follows:
> Start Time (s) = 0.001
>Time step (s) = 1e-05
>Number of steps = 100
- Now go to Solution > do Initialization > select Method=Hybrid > Initialize. Check the console if the solution is inialized or not.
- After Initializing > click on Patch > select Phase= fluid i.e. engine oil/n-heptane(selection depends on which case we are running) > select Variable=Volume Fraction > go to Volume Fraction Patch Options and click on Volumetric smoothing and set factor as 0.5 > now go to Registers of Patch > select the specified region name > click on Patch.
- Create Contours and also solution Animations for the Contours.
- Before running the calculations, go to Solution > click on Controls > then a task pages opens showing the Solution Controls > set them as follows;
- Before running the calculations, go to Run Calculation > double click on Run calculation and set the following settings;
- Press Calculate to Run the simulation. Once the simulation completes save the animation.
Result:
case-1 20% Immersion, Fluid - Engine oil.
Residuals:
Contour:
Animation:
Observation:
The gears at the initial stage are in idle position and the fluid-engine oil is at the bottom of the gear box with assigned 20% fluid region. Splashing of lubricant oil helps to spread on all the interior parts of gear box. As observed, number of teeth immersed in the fluid is very less due to this the amount of fluid carrying during rotation is very low. The animation shows that in this case oil is not effectively covering all the parts of gearbox this is due to lower level immersion of gear teeth in engine oil. Here we can see that the lubricant is not distributed properly and hence their heat dissipation rate would reduce which effects to increase in the tooth temperature as well as effects the overall performance of gearbox in long run. Using this fluid for lubrication gives a very low sloshing effect.
Case-2 30% Immersion, Fluid - Engine oil.
Residuals:
Contour:
Animation:
Observation:
The gears at the initial stage are in idle position and the fluid-engine oil is at the bottom of the gear box with assigned 30% fluid region. In case of 30% fluid region, almost half of the gear teeth are immersed in the engine oil. This gives sufficient lubrication to fill the gap between the gears from the initial stage . When compared to the first case, splashing of the engine oil helps to cover on all the parts is more effective and the amount of oil that is sliding down will be more when compared to the initial case. Hence in this case, the gears are operated with sufficient lubrication for a longer time and also minimises the problems of heating in gears. Thus performance of gear box is good. Using this fluid for lubrication gives a very low sloshing effect. Engine oil is a kind of sticky substance which can stay some tyme on the teeth.
Case-3 20% Immersion,Fluid-n-heptane (c7h16).
Residuals:
Contour:
Animation:
Observation:
The gears at the initial stage are in idle position and the fluid-engine oil is at the bottom of the gear box with assigned 20% fluid region. The contour shows the 20% n-heptane liquid is not effectively reaching all the teeth, due to the lower level of immersion of gears in n-heptane liquid. As observed, number of teeth immersed in the fluid is very less due to this the amount of fluid carrying during rotation is very low.As the viscosity is low for n-heptane liquid, it doesnot stick to the surface of the teeth, instead tends to slide from the teeth. Hence more consumption of fluid is necessary to maintain the temperatures. Siilar to the case 1 the quantity of fluid is low in order to circualate the entire gearbox, which effects the tooth temperatureand sometimes may lead to failure.
case-4 30% Immersion,Fluid-n-heptane (c7h16).
Residuals:
Contour:
Animation:
Observation:
The gears at the initial stage are in idle position and the fluid-engine oil is at the bottom of the gear box with assigned 30% fluid region. Here enough teeth are immersed into the fluid as it is increased from 20% to 30% fluid region. With help of 30% region filled with n-heptane fluid , it helps to lubricate all the teeth effectively and sloshing is also little mre as compared to the 20% of immersion. As the viscosity is low in this case the fluid material doesnt stay on the teeth for long durations when compared to the engine oil. Hence in this case, the gears are operated with sufficient lubrication and minimises the problems of heating in gears. In this case we can see higher sloshing effect as it has a low viscosity.
Conclusions:
- Simulation of gear box is performed with two different fluids by varying their percentage of region in immersion i.e. 20% & 30%.
- On comparing the regions of immersion, it is clear that 30% of immersion region is more effective in lubricating all the teeths of the gears in a better way. If the gear is immersed 30% in the fluid and tend to move then sufficient amount of lubrication is passed in between the gaps of the teeth for this region.
- In all the cases splashing of fluid is observed but this depends on the particular properties of Fluid as well as the type of material/ fluid we are selecting.
- On comparing both the fluids that we considered here, engine oil has more benefits when the gears are operating at higher temperatures as the viscosity of oil is more when compared to the other fluid.
- As Engine oil has high viscosity, it can stay of the teeth for little longer time when compared to n-heptane fluid.
- In this case of gear box higher the value of viscosity results in lower oil consumption and produce lower wear during the motion of gears.
- Sloshing effect is accepted in lubrication to certain extent, if the limit exceeds then consumption of fluid will increase.
Part-2
# Dynamic Meshing Model:Dynamic mesh is a tool in which the computational grid changes dynamically during the run of the CFD simulations. In this kind of mesh models the boundarries of the cell zones are permitted to move with reference to the other boundaries of zones and hence the mesh is adjusted accordingy. The boundaries can be moved rigidly with reference to both the gears i.e. in linear and rotational motion. The motion of boundaries can be rigid,such as pistons moving inside an engine cylinder or a flap deflecting on an aircraft wing etc. In both the cases the nodes that define the cells in the domain must be updated as a function of time and hence the dynamic mesh solutions are inherently unsteady.case of dynamic mesh motion is called the sliding mesh in which all of the boundaries and the cells of a given mesh zone move together in a rigid-body motion. In this 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. Furthermore, mesh zones moving adjacent to one another can be linked across one or more non-conformal interfaces. As long as the interfaces stay in contact with one another (that is, “slide” along a common overlap boundary at the interface), the non-conformal interfaces can be dynamically updated as the meshes move, and fluid can pass from one zone to the other. A method by which the solver can be instructed to move boundaries or objects and to adjust the mesh accordingly.Internal node positions are automatically calculated based on user specified boundary/object motion,cell type, meshing schemes. On enabling the Dynamic Mesh there are three various methods provided in order to update the volume mesh to the motion defined at the boundaries.
Mesh Methods:
- Smoothing- It is bascially used to adjust the meshthe zone with a moving/deforming boundary, internal nodes of the mesh move but the number of nodes and their connectivity remains constant. Here the internal nodes absorb the movement of the boundary.
- Layering- It is used to split/merge the cells that are adjacent to any moving boundary. But it should satisfy the two conditions; (a) All the cells adjacent to the moving face zones are either wedges or hexadral even if the cell zone contain mixed cell shapes. (b) The cell layers must be completely bounded by one-sided face zones ,except when sliding interfaces are used.
- Remeshing- If the boundary displacement is largewhen compared to the local cell sizes, the cell quality can become degenerate if only the mesh smoothing is used. This will show in the negative cell volumes and consequently it will lead to the convergence problems when the solution is updated to the next time step
Example:
- Automotive piston moving inside a cylinder.
- A flap moving on an airplane wing.
- A valve opening and closing.
- An artery expanding and contracting.
Advantages:
- Here it helps the boundary can move rigidly w.r.to. each other both linearly and in rotational motion.
- The dynamic Mesh Model can be can be applied to single or multiphase flows.
- The mesh zones moving adjacent to one another can be linked across multiple non-conformal interfaces.
Disadvantages:
- The convergence problems occur when the solution is updated for the negative cell volume.
- If the boundary displacement is largerwhen compared to cell sizes, the cell quality can deteriorate.
# Fluid Sloshing Effect :
Sloshing is the periodic motion of the free surface of a liquid in a partially filled tank or a container that can be caused by any disturbance to a partially filled liquid container. The liquid must have a free surface to constitute a slosh dynamicsproblem,where the dynamics of the liquid can interact with the containerto alert the systemdynamics effectively. Anti-slosh devices are widely used in order to limit the adverse liquid slosh effect on the directional performance and the stability of the vehicles. Baffles are used as sloshing suppression devices in order to controll sloshing. Hydrodynamic forces and moments arising from liquid cargo oscillations in the tank under steering and braking maneuvers reduce the stability limit and controllability of partially filled tank vehicles.Optimizations and sloshing reduction techniques in fuel tanks such as ellipitica tank, rectangular,oval and generic tank shape have been performed in different filling levels using numerical, analytical analyses. 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 amount of liquid seem to lead a resonance effect. Many of the balls for roller of hockey commonly available already contain water to reduce the bounce height.
Examples:
- Airplane fuel storage tanks.
- Missiles with liquid tanks.
- Satellites (sloshing in low gravity fiels applications).
- Tanker vehicles.
- Hull of ship transporting oil from a rig.
Sloshing of the liquid in the storage containers may result in the negative effects such as deformation and sometimes failure of tank walls due to the heavy impact of sloshing.If an open tank is subjected to ground motions, sloshing may lead to to the spillage of the inside liquid. Hence sufficient clearance is required to provide between the free surface and the top of the tank .
#User Defined Function(UDF):
User Defined Function is a function that is programmed and can be dynamically loaded with the fluent solver to enhance the standard features of the code. The UDF's are implemented in fluent code as macros. They have an include statement for the udf.h file. They access data from the fluent solver using predefined macros and functionssupplied by Flunet. UDF's are executed as either interpreted or compiled functions in Fluent. For interpreted UDF's, source files are interpreted and loaded directly at runtime, in a single step process.
Uses of UDF:
- Initialization of a solution.
- Adjustment of computed values on a once per iteration basis.
- Post processing enhancement.
- Enhancement of existing Fluent models i.e. discrete phase models, multiphase model etc.
- Customization of boundary conditions , material property definitions, surface and volume reaction rates, diffusion functions, etc.
Udf used in the challange:
# Errors that occurred in the simulation.
a. Dynamic mesh failed error-
b. Negative cell volume detected error
If the mesh is course it should be refined so as to elminate the error. Always the time steps should be set according to the problem we are performing.The negative cell volume error is displayed when the mesh has been updated in a way to cause a negative cell volume. Factors for causing this error are; overlaping nodes and significant mesh motion(relative to cell size)per step. By reducing the time step we can avoid major mesh displacements. Skewness is the angular measure of a cell with respect to its adjacent cell. Highly skewed cells can be decrease the accuracy and doesnot allow the solution to stabilize. Using the local remeshing method fluent marks the cells based on the skeweness and minimum and maximum length cales as optional sizing function.
Animation Links -