Week 4: Project - Transient simulation of flow over a throttle body

Aim:

• To perform the Transient State Simulation over the throttle body in Converge studio and observe the plots of pressure, Velocity, Mass flow rate and the total Count cells.
• Post Process the result using Para view and shows the Pressure and Velocity Contours and made a animations for the flow with a different angles to demonstrate the flow over the throttle body in both scenarios.
• Changing the position of the throttle values according to the change in time.

Introduction:

A throttle is the mechanism by which fluid flow is managed by constriction or obstruction.

An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term throttle has come to refer, informally, to any mechanism by which the power or speed of an engine is regulated, such as a car's accelerator pedal. What is often termed a throttle (in an aviation context) is also called a thrust lever, particularly for jet engine powered aircraft. For a steam locomotive, the valve which controls the steam is known as the regulator.

In an internal combustion engine, the throttle is a means of controlling an engine's power by regulating the amount of fuel or air entering the engine.

For a gasoline engine, the throttle most commonly regulates the amount of air and fuel allowed to enter the engine. Recently, for a GDI engine, the throttle regulates the amount of air allowed to enter the engine. The throttle of a diesel, when present, regulates the air flow into the engine.

In fuel injected engines, the throttle body is the part of the air intake system that controls the amount of air flowing into the engine, in response to driver accelerator pedal input in the main.

The calculations on how to calculated an end time for the simulation:

In order to define the simulation time i.e. how much time we required to run the simulation

First we measure the characteristic length of the pipe through the fluid flow

we can find that the length of the pipe is 0.2 m (approximately)

The velocity at inlet from the Steady state simulation is 190 m/sec

Therefore the time pass to flow the fluid in the domain is = The characteristic length/velocity of the flow

=0.2/190=0.00105 seconds (for one-time flow of fluid)

This small time is not enough to capture the physics in our domain so we increased the simulation time in order to capture the physics more approximately we take the end time as 10 *0.001 is 0.01 micro seconds.

Importing Geometry and Assign the boundary:

Import the geometry into the Converge studio and clean up the geometry by using some tools which are available in the converge.

Geometry with Thickness:

Delete the thickness part of the throttle body which is not necessary for us. After completed this process then we have free edges by using the patch command we can close the free edges.

Geometry without Thickness and Closed the free edges:

Enable the vectors on the geometry make sure that all the normal should be facing inside the fluid domain The below figure shows the vectors inside the domain where the fluid is going.

Now check for the errors in the geometry by opening the diagnosis dock and then find if no errors are there means we can proceed to the case setup.

Now Assign the boundaries name to the geometry

Case setup for Simulation:

• Application Type – Time Based
• The flow is general flow which contains the air as a Material.
• Air contains a Species mixture of O2 and N2 which will flow through the required geometry.
• Global Transport Parameters the Prandtl number is 0.9 and the Schmidt number is 0.78.

Simulation Parameters:

• In the Run Parameter: Solver we used is Steady state and the simulation mode = Full hydrodynamic in the mic state we enable the Solver Momentum, Solve Species.
• In Simulation time Parameters we set the values for start time as 0 seconds and end time 0.01 seconds and the initial and Minimum time setup for 1e-9 and remaining values are put to default.
• In the Solver Parameters, the Navier stock equation should be Pressure based solver and remaining should be default.

Initialization and Boundary Conditions:

• In the initialization region change the name of the Region as a volumetric region and the values assigned for the temperature and pressure is 300k and 101325.0 Pascal and add the species O2 and N2 with the mole fraction of 0.23 and 0.77.
• The pressure at the inlet is 150000 Pascal and the temperature should be 300 k and the boundary type is INFLOW
• The pressure at the outlet is 100000 Pascal and the temperature should be 300 k and the boundary type is OUTFLOW.
• For the Elbow wall boundary should be the wall type with a Law of wall boundary condition and temperature should be 300k.
• For the throttle the boundary type is WALL type with the Law of wall as a boundary condition and temperature should be 300k and also included the file in order to revolve the throttle value in the domain.The values which are used to rotate the Throttle valve are provided below.
• For taking the rotation center and rotation about the following steps can be followed
  • • Go to measure → Direction→ Arc normal → select any three vertices → apply

    Or

    • Go to measure → Direction→ Triangle normal → Select any one triangle → apply

    In the message log the results will be display so we can copy that numbers and paste it the rotation centre and rotation about and turn on the use file and click on the gear option it opens the dailogue box enter the values of rotation angles as shown below.

Physical Models:

• In the physical models enable the Turbulence Modelling and the solver should be selected as RNG K-e and put the remaining values as a default.

Grid Control:

• In the Grid control enable the Fixed Embedding and Base grid
• Enter the base grid values and then go to the fixed Embedding add the
• Entity type=Boundary
• Boundary ID=Throttle
• Mode =Permanent
• Scale=2
• Embedded layers=3

After entered all the values click on apply.

Output and Post Processing:

• Post variable Selection and Output files are the default values.
• In the output files we have given time interval to write the 3D output data=0.0001 seconds, thus the outputs of the simulation files be stored after 0.0001 seconds.it gives 100 output files.

Post-Processing:

I have done the post processing of the results for all three cases using the converge studio and paraview. Post processing is actually used in order to get the desired Output by running the simulation

Results:

Mesh Profile:

As we can observe that the mesh around the throttle is due to the use of embedded layer.

Mesh Animation:

As the throttle valve rotates the mesh around the throttle valve changes which we can observe clearly in the video.

Velocity Contour:

Velocity Contour with Streamlines and Vectors:

Velocity Contours on the faces of the Throttle:

• The velocity is high at the junction (indicates red colour) is due to the amount of air particles passing through them is less and also the area is less so the velocity is increases and the other side the pressure is more so that the velocity is less.By observing the vectors image the vectors at the where the velocity is high at that point the vectors are passing through it whereas on the other side the vectors are diverging and going out of the surface so that the velocity is less.
• The pressure energy is converted into the kinetic energy so that the velocity is significantly start increasing after passing through the throttle body because the throttle value is not completely sealed with the walls.so that the velocity obtained at the velocity is 290-300 m/sec.

Velocity Animation:

Velocity Streamlines Over the Throttle Valve:

The velocity is changing from when the throttle valve rotation takes place when the throttle valve is rotated for 4 milli seconds the rotation of angle is 25 the stream lines above the throttle valves achieve the highest velocity clearly observed in the video with the red color contours when it comes to its original position the velocity contours changes the color to yellow and green the velocity is in range of 200-300 m/sec.

Pressure Contour:

Pressure Contour on Throttle body:

• The pressure is high at the one side and the other side the pressure is minimum.
• As the pressure is high at the throttle body where the fluid first interacts with the throttle body indicates with Red colour when the pressure is directly hits the body and the lower pressure is at the places where the surface of the wall and the throttle body interacts.
• The pressure gradient is formed after the attack of air particles on the throttle body so that the pressure is reduced and moves toward the outlet.This is main reason to drive the fluid in the system.
• The low pressure is observed on the wake region.The recirculation of air is caused by the viscous airflow around the throttle valve surfaces.
• When the throttle valves rotates the pressure is also changing when it is at rotation of 25 degrees one side the pressure is very high and other side is low pressure as we clearly observed the images of the throttle value provided above.

Pressure Animation:

Pressure over Throttlevalue for Transient state Animation:

Mass flow rate plot for the Transient state of Throttle Body:

• The mass flow rate is drastically increased in between the 0-0.002 seconds because the Throttle valve changing its position and from 0.002-0.004 the Throttle valve remains constant so the mass flow rate is constant and from there it increases rapidly because the throttle valve comes for its initial position from 0.004-0.008 and from 0.008-0.010 the mass flow rate is constant because the throttle valve attains its initial position.

Velocity plot for the Transient state of Throttle Body:

• The Velocity is drastically increased from 0-190 m/sec in between the 0-0.002 seconds because the Throttle valve changing its position and from 0.002-0.004 the Throttle valve remains constant so the velocity rate is constant and from there it increases rapidly because the throttle value comes for its initial position from 0.004-0.008 i.e from 160 m/sec to 240 m/sec and from 0.008-0.010 the velocity rate is constant i.e 240 m/sec because the throttle valve attains its initial position.

Total Pressure plot for the Transient state of Throttle Body:

• Total pressure in the domain before its enter at the inlet is 150000 Pascal kept constant and the outlet pressure given is 100000 Pascal as the simulation starts running the outlet pressure starts changing its nature and fluctuations for up to 0.008 seconds this is because of the movement of the throttle valve and when the throttle valve is in its original position it achieves the convergence so the static pressure after 0.008 seconds is constant.

Static Pressure plot for the Transient state of Throttle Body:

• Static pressure is the pressure of the fluid at rest i.e when the fluid is not entered into the domain at the inlet is 150000 Pascal and once the air is allowed into the domain as the simulation starts the inlet static pressure starts changing its nature and fluctuations for up to 0.008 seconds and achieve the convergence after that as the pressure is flowing from the high pressure region to low pressure region and the outlet static pressure is 100000 Pascal because at the outlet no fluid moment is there.

Total Number of Cells Count for the Transient state of Throttle Body:

• The change in geometry by generating mesh for each second leads to the different number of cells counts when the Throttle valve is rotating.
• When the Throttle valve is Stationary the cell counts remains same i.e observed between the time seconds of 0.002-0.0004 and also at 0.008-0.01
• When the Throttle valve is moving the mesh generates also changes so that the number of cells also changes i.e we observed in the time intervals between 0-0.002 and 0.004-0.008 seconds.

Conclusions:

• Transient state simulation of throttle valve in converge studio and generated the contour and plots successfully.
• Highly turbulent flow is observed after the Throttle valve as the value changing its position over the time period.
• CFD analysis has been done to understand the airflow pressure and flow velocity caused by the throttle valve at different opening condition.