Transient simulation of flow over a throttle body

• Given Problem:-

Q. Simulate Flow of fluid over a throttle body in converge studio and post process the results

• Software used-

1. Converge CFD Software

2. Cgywin

3. Paraview

• Throttle body Step design-

• Steps Involved while solving this challenge-

1. We first download the required geometry from the website of skill lync.

2. Set the case setup according to the given problem in the challenge. As this is transient state challenge we have set the case as transient state challenge.

3. Now we will check the given case for any problem and the export its files for running it into cgywin.

4. Cgywin willl create the output files of the case by solvig 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 result more clearly.

6. Now by using Converge software line plotting option, we will plot the graphs for Velocity, pressure and Mass flow rate.

• Case setup Important Parameters:-

1. Inlet Pressure- 150000 pa

2. Outlet Pressure- 100000 pa

3. Starting Time- 0

4. Ending Time- 0.01 Second

5. Solver- Transient

• Throttle profile info:-

• From 0 to 2 ms the valve should rotate by 25 degrees.
• From 2 to 4ms it should stay at 25 degrees.
• After which by 8ms the valve should get back to it’s original position

• Calculating end time:-

Lenght of throttle body in x direction- 0.106 or take it as approx 0.2

Average Velocity- 80 m/s.

Time taken to flow through pipe- 0.2/80= 0.0025

so lets take it as 0.01 seconds to run it for different cases.

• Mesh, Velocity, pressure contour and plots

Fig.1.1 Mesh Profile of geometry

Fig.1.2 Velocity profile(Throttle started rotating)

Fig.1.3 Velocity profile(Throttle at 25 Degree)

Fig.1.4 Velocity profile(Throttle return to 0 Degree again)

Fig.1.5 Velocity profile(Throttle at 25 Degree)

Fig.1.6 Pressure profile(Throttle started rotating)

Fig.1.7 Pressure profile(Throttle at 25 Degree)

Fig.1.8 Pressure profile(Throttle return to 0 Degree again)

Explanation:-

1. Fig. 1.1; Its an slice view of geometry. We can see the surface with edges. As you all observe that near throttle position the edges are very dense. This is due to fact that we have done embedding on throttle area. The embedding increases edges count by multi fold. Now these edges will help us to simuate the case more precisely as number of cells increased.

2. Fig, 1.2; Velocity Profile which consist glyphs and streamlines to help us understand the case more better. The picture is taken when throttle started moving. As we can see that before attacking throttle the fluid velocity is less compare to outlet. As the throttle rotate and block the path, the fluid increases its speed to maintain the mass flow rate and hence velocity increases after passing through throttle.

3. Fig. 1.3; As throttle rotate further and achieve 25 degree angle, the fluid will encounter more resistance in flow. Hence we can see red stream stream lines near throttle which signifies the sudden increase in velocity due to reduction in flow area. However the velocity at inlet part is still less due to throttle resistance.

The stream lines get disturbed greatly due to rotation of throttle. Now turbulent flow is created near throttle and hence it is transient flow now.

4. Fig. 1.4; This picture is taken when throttle again takes its 0 degree position. As we can see clearly that velocity at inlet side is increased suddenly. Velocity at outlet is also increased by some factor. When throttle moves back to 0 again then stream lines will not facing any major resistance and hence they move quicky to fill the void created by throttle and hence velocity increased.

5. Fig.1.5; Throttle is at 25 degree angle. As you can see clearly that at upper and lower part of throttle the velocity is the highest compare to other throttle area. This due to fact that at these two points the fluid is flowing and crossing throttle. But due to small flow area due to throttle, the fluid is increasing its speed to maintain mass flow rate. Hence we can see the sudden spike in velocity near that area.

6. Fig.1.6; When throttle starts rotating then pressure is highest at inlet as velocity is lowest at inlet. Furthermore the pressure in inlet is higher then outlet so that flow can occur. Inlet pressure is 150000 pa vs 100000 pa pressure at outlet.

7. Fig.1.7; When throttle reaches 25 degree angle the pressure at inlet side become very high due to low velocity. And pressure at outlet become lower.

8. Fig.1.8; When the throttle reaches 0 again then the pressure drops down at inlet as velocity increases and pressure remains approx same at outlet.

• Plots-

Fig. 1.9 Mass Flow rate variation during flow

Fig. 2.0 Average Velocity variation during flow

Fig. 2.1 Total Pressure variation during flow

Fig. 2.2 Total Cell count variation during flow

Explanation:-

1. Mass flow rate is varying very quickly due to rotation of throttle.

2. Velocity and total pressure at outlet are also varying due to rotation of throttle.

3. Cell counts are changing very quickly due to rotation of throttle.