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

AIM :- Transient simulation of flow over a throttle body.

OBJECTIVES :-

• Setup throttle valve model in converge.
• Study the variation of flow parameters.
• Post process the results and documentation.

SOFTWARE USED :-

The following are the different software used while creating whole challenge are-

1. Converge studio v3.0 ( in which I drop down the geometry then it scaling and setup the all case and finally exporting all the files)
2. Cygwin/Command prompt to run the case with the help of converge science.
3. Paraview in which showing different contours, animation files and movement of throttle valve.

THEORY AND INTRODUCTION :-

In recent years, the main concern for human society is hazardous, pollutants emitted by various sources. One such source is the exhaust emissions from the automobiles. In order to control these emmisions without sacrificing the performance of the engine, conventional corborator is found tobe inadequate. It is mainly because, with carburator, it is difficult to mantain the required air fuel ratio throughout the engine operating range. This led the automotive industry to change over to electronically controlled fuel injection systems in modern vehicles, which uses electronically controlled unit (ECU) and can maintain the required air fuel ratio throughout the engine operating range. The ECU calculates the required amount of fuel tobe injected based on the engine operating conditions.

In the conventional throttle body, if a throttle gets struck in the open position, the driver could generally put a toe under the accelarator and lift up. Occassionally after servicing or repair, the wire or cable between the accelerator and throttle would not be correctly reinstall causing sudden acceleration. The purpose of the bypass screw is to adjust the amount of air going pass the throttle plate. This screw does not controll idle speed. It sets the amount of air going through the bypass port in the throttle body by changing the relationship of the throttle blade to the bypass port.

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 the inlet gasses (by the use of a throttle ) but usually decreasesd. The term throttle has come to reffer informly, to any mechanism by which the power or speed of an engine is regulated, such as car's accelarator padal. What is often term 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.

Transient analysis means analysing a system in unsteady state. If the variable involved in defining the state of a system does not vary with respect to time, then the system is said tobe in steady state. If not, it is in unsteady state.

Examples are-

1. A hot coffee put in a air (transient heat transfer).
2. Just after switching on a capacitive circuit (transient voltage current charecterastic in capacitor)
3. An iron piece exposed to carbonaceous during surface hardening process ( transient mass transfer).

IMPORTANT STEPS :-

While setup the case and for completing challenge I adopted following steps as-

1. We have to first download the required geometry from the skill-lync website.
2. Setup the cases according to the given problem in the challenge. As transient state challenge we have to set the case as transient state challenge.
3. Now we will check the given case for any problem and the export it's files for running it into cygwin.
4. Cygwin will create the output files of the case by solving them.
5. Now we will open paraview software and open the case there. We will use glyph and streamline option to visualize and post process the results more clearly. Also rotating the throttle valve as written in the case set up like- From 0 to 2 ms the valve should rotate by 25 degrees, From 2 to 4 ms it should staty at 25 degrees, After which by 8 ms the valve should get back to its original position i.e. -25 degrees.
6. Now by using converge software line plotting option, we will plot the graphs for velocity, pressure, mass flow rate and total cell count.

CASE SETUP :-

Actually setup of transient state is nearly same as that of steady state simulation and which part are different that's are showing below-

1. Custom time unit in output files :-

Here, I defined custom time unit and conversion factor as zero.

2. Post convert :-

This is post convert files, for which required 6 seconds to convert in VTK in-line binary format, by giving any case name.

3. Rotation of throttle valve :-

Here, I rotate the throttle valve by fixing the surface movement, UDF condition is Law of wall, I write rotation rate file also I write Rotation centre and rotation axis. Temperature boundary condition and Turbulent kinetic energy is 'zero normal gradient' . Rotation about axis is zero about Z-axis because throttle valve is in XY-directions. Here is no torque so that torque centre not considered.

4. Run parameter for solver :-

Here I I used transient solver, time based simulation type for full hydrodynamic mode and compressible gas flow solver. Full hydrodynamic for developed region and transient for throttle valve rotation according to time.

5. Simulation time parameter :-

For simulation time parameter I used following data-

Start time = 0 sec,

End time = 0.01 sec,

Initial and minimum time step = 1e-9 sec,

Maximum time step = 1 sec,

Maximum convection and diffusion CFL limit = 1 sec,

Maximum convection CFL limit = 1,

Maximum diffusion CFL limit = 2,

Maximum Mach CFL limit = 50,

and all others are by default values.

6. Writting time interval of output files :-

Here writting following data-

Time interval for writting 3D output data file = 0.001 sec,

Time interval for writting restarting output = 1e-6 sec,

and remaining all are by default values.

PLOTTING RESULTS :-

Following are the resulting plots which shows that the results i.e. output for the creating simulations. Plots clearly proves that the exact results for the given conditions are as follows-

1. Mass flow rate for inlet :-

Mass flow rate start from zero and later on it decreases according to time interval increases. As we use compressible full hydrodynamic flow, mass flow rate automatically decreases as shown in above plot.

2. Mass flow rate for outlet :-

At outlet mass flow rate increases as time ncreases, as shown in above plot.

3. Pressure contour for surface with edge :-

This shows pressure contours for surface with edge where, minimum pressure is 70,000 pascals and maximum pressure is 1,40,000 pascals. About throttle valve griding size is more that's why there have low pressure.

4. Pressure contour for surface :-

This is the pressure contours for surface, where minimum pressure is 70,000 pascals and maximum pressure is 1,40,000 pascals as shown above.

5. Pressure contour plot :-

Here pressure increases step wise as time increases because compressible solver ere used.

6. Pressure plot in converge :-

This is the pressure plot, where we can see that from start pressure goes to increasing and later on it decreasing contineously after it reaching at peak value.

7. Total cell plot :-

As gridding size is precise the number of total cell automatically increases because its directly proportional, and it consant throughout the whole time.

8. Velocity contour for surface with edge :-

Here showing velocity contour for surface with edge as minimum value is 42 m/s and maximum velocity is 290 m/s. At throttle valve velocity also very less because of thre have very less griding size.

9. Velocity contour for surface :-

For Velocity contour for surface results are very same as velocity contour for surface with edge, only difference in griding thickness.

10. Velocity contour plot :-

This is the velocity contour where velocity decreases as time increse beacause of full hydrodynamic flow of compressible solver.

11. Pressure animation :-

Here showing clear results for pressure contour with the help of MPEG animation file. Here showing that how throttle valve and contour changes with respect to time.

12. Velocity animation :-

This is the animation file for velocity cotour. In this animation file velocity changes and showing that at where velocity is affects. At throttle valve veocity is moderate because of there have very less griding size.

CONCLUSIONS :-

From above results we can coclude that the pressure, velocity...etc affects on gridding size. If griding size is ery small then no more effect occure on that part. Griding size is the most important part of the simulation.

Also, throttle valve rotates up and down according to the axis rotation is taken from centre of the throttle valve.

For rotation of the any part like here throttle valve we can use transient simulation.

The fixed embeding mesh provides satisfactory reslts and mesh is proparly reoriented even in case of rotation of throttle valve. The average velocity is observed tobe around 210 m/s, which is quite close to the one used for calculation of simulation time, determined by steady state simulation of the same geometry.

In this way, I completed this challenge by describing and showing everything which required to analyse the results and I write detailed report for output results. Transient simulation is the easy way to rotate any part about there axis.