Discretize the Intake manifold & Analyze the Effect of Discretization length on Simulation time & Performance parameter by use of GEM 3D & GT-ISE

 Title : Discretize the Intake manifold & Analyze the Effect of Discretization length on Simulation time & Performance parameter by use of GEM 3D & GT-ISE

Objective: 1. Set the discretization length 0.1mm & compare with default case 40mm length

                2. Understand effect of discretization length on Simulation time & Performance parameter.

                3. Explore Building intake manifold from STL model in GEM3D 

 Theory:

Importance of discretization 

                           The discretization length is one such attribute that is not intuitive. The solver divides pipes into subvolumes, upon which calculations are conducted. The sub-volume length is the discretization length. For engine modeling the recommended value of the discretization length is 0.4*(cylinder bore diameter) on the intake side, and 0.55*(cylinder bore diameter) on the exhaust side. The difference between the two values is due to the difference in the speed of sound as a result of the temperature difference.

       Discretization is the splitting of large parts into smaller sections to improve a model's accuracy. There are two ways in which a fluid system is discretized. The first is to break the system up into several different components such as several pipes and/or flowsplits. The second is by discretizing a 'Pipe∗' part in to multiple sub-volumes, each performing their own calculations. When a pipe is discretized (by selecting discretization length to be shorter than the pipe length) the result will be the same as if several shorter single-volume pipes would have been used instead of one longer pipe.

The discretization lengths will affect computational time in a slightly different way for each solution method. For both the explicit and implicit solution methods, computational time will be higher for smaller discretization lengths, because there will be more sub-volumes in the system that require calculation of pressure, temperature, etc. In other words, there are more solution variables. In the explicit solution method, the discretization length also affects the simulation time step. The time step is proportional to the discretization length due to the Courant condition discussed previously. Smaller discretization lengths will require smaller time steps, and thus more computational time. For the implicit solution method, the time step is imposed as a constant value, and therefore simulation time is just a function of the number of subvolumes in the system.

 

 

 

 Make the parameter of discretization length

 

 

 

                               

                               

                            

Case 1 : Discretization length (40mm)>Brake power =36.3kw

Case 2 : Discretization length (0.1mm)>Brake power =36.2kw

•   for Disecretization length 0.1mm  brake power is 0.27% less

 

Case 1 : Discretization length (40mm)>Brake Torque =96.2N-m

Case 2 : Discretization length (0.1mm)>Brake Torque =95.9N-m

•   for Disecretization length 0.1mm  brake Torque is 0.31% less

 

Case 1 : Discretization length (40mm)>BSFC =238.2 g/Kw-h

Case 2 : Discretization length (0.1mm)>BSFC =238.9 g/Kw-h

• for  Disecretization length 0.1mm  BSFC is 0.29% more

 

                          

Case 1 : Discretization length (40mm)>Max cyllinder Pressure =117.11bar

Case 2 : Discretization length (0.1mm)>Max cyllinder Pressure =115.18bar

• for Disecretization length 0.1mm Max cylinder Pressure is 1.67% Less

Cylinder pressure

Simulation Time

Case 1 : Discretization length (40mm)>Factor of Real- time=3.83sec

Case 2 : Discretization length (0.1mm)>Factor of Real- time=13220sec

Simulation time

from above graph we can see that computation time for case 1 & 2 

Case 1 : Discretization length (40mm)>Computation time=2.65min

Case 2 : Discretization length (0.1mm)>Computation time=33.89min

• for Disecretization length 0.1mm simulation time is 12.7% more

 

Part II: Explore the tutorial N0.2 (GEM3D): "Building intake manifold from STL File"

GEM3D software Use

                       GEM3D is a graphical 3D tool used to build and discretize flow systems for use with GT-SUITE. It
provides the ability to build models using component templates, import shapes from an STL file, connect complete flow systems, dimension the model, and automatically discretize. The resulting discretized model from GEM3D is compatible with GT-SUITE and can be opened directly using GT-ISE.

Step1:Getting Started

Launch GEM3D and create a new model file by selecting File/New Document or New from the Home tab and clicking on Finish making sure that the Document selection on the left is set to GEM3D (.gem).

    

Step2 :Importing a Shell from an STL File

The first step is to import the intake manifold from an STL file that is provided with the GT-SUITE installation. To import the shell, select Import 3D from the File group in the Home tab. This will launch the Import 3D Wizard, shown below.

Browse for the plenum.stl file located in the GTIHOME\v20XX\examples\Acoustics\Non-Linear_(standard) directory

   

                

Step3 :Separating Sections by Curves

1.inlet and the ends of the 4 intake runners are closed.,We need to remove these caps so the ends are open and available for flow.

2.To do this, we will use the Separate By Curves operation. This will separate the geometry into parts based on changes in the surface of the object.

3.This process will also separate the intake runners into two different sections near the area change at the top of the runners.

5.The tolerance controls how sensitive this operation is to changes in the surface area of the part. A Tolerance of 1.0 should be used for this operation

6.Now that the end sections of the runners and plenum are separated from the main shape, we can delete them from the model.

7.To do this select the 5 end sections (remember to hold down Ctrl to select multiple shapes)and press the delete key

8.This will open a confirmation dialog verifying that you want the mesh shapes deleted. Click Yes and the model should look like the image below, where the inner surfaces are now partly visible through the open ends where the caps were removed.

                      

Step4 :Using the Cutting Plane

1. Now that the end caps have been removed, we can continue separating the shape into sections that can be represented by pipes and flowsplits.

2. We will start by separating off the 4 runners from the manifold since the runners can be represented by pipes. To do this we will make use of the cutting plane operations available in the Cutting Planes group in the Convert tab.

3. To enable the cutting plane, select 3 Points Cutting Plane from this group.A cutting plane can then be created by clicking on 3 points on the model to define a plane. Since we want to cut off the runners, let's pick 3 points on the underside of the manifold block as shown by the black crosshairs in the image below.

                           

                   

4.To do this, select Clip Shape from the Shape Operations group in the tab Convert, or select press the Clip button in the Plane Control window.

GEM3D will separate the mesh shape along the cutting plane and create the new mesh shapes, as shown in the image below.

                         

Step5:Converting Sections into Flow Components

1.Once we have sections that can be represented by pipes or flowsplits we need to convert them into flow components.

2.This is done with the convert mesh operation. To begin the conversion, right-click on the first section of the first runner (grey colored bent section in the image above) and select Convert Shape to Component. This will open the convert mesh window, shown in the image below.

                    

Check the flow from point 1 to 2 , otherwise rearrange . Also need to slelect flow volume as this only runner so, we select the pipe

             

Geometery select depends upon the bend type . so, here there is selectmultiple bend type. Select port size defination. check the diameter by custome plane & based upon this select the diameter 48.6mm. for part2 select the define from part 1, because we want uniformity in the pipe.

 

wall thickness should be 1mm.

Define the initial state object i.e Air . By enter in to the use folowing procedure

 

 

 

                            

likewise all multiple bend pipe convert to pipe 

Convert intake port into pipe

like wise we have to convert other bend in to pipe

                

Delete unwanted part

Step6: Adding a Custom Connection

1.In the conversion process for the runners, information regarding the curved entry from the manifold (fillets) was lost.

2.This curved entry would represent a better flow transition than a default orifice connection, so we need to manually add an orifice connection to represent this.

3.To add a custom orifice to a flow component right-click on the first section of runner 1 (blue component in the image above, "run1-1") and choose Add Connection

 

Step7: Adding a Subassembly Connection to Impose Connection Direction(Inlet & outlet)

The next thing we want to do is specify the end (boundary) connections, meaning the connections that do not connect to anything. In our model the ends of each runner need an end connection specified. This is done with a special subassembly connection. To add the subassembly connection right-click on the end section of the first runner component ("run1-2") and choose Add Connection. This will open the port connection window, shown in the image below.

 

step 8:Dividing Pipe Sections with Area Changes

     Now that we have the runners converted, let's move to the other end of the manifold. The entrance appears to consist of a pipe section with a round and D-shape, then a 90 degree turn into the manifold. The straight section can be converted into 2 pipes, one representing each effective diameter. Therefore we need to cut and separate these two sections so they can be converted. Since they are pipe sections, we can utilize the pipe normal cutting plane operation. From the Cutting Planes group in the Convert tab, choose Pipe Normal Cutting Plane.

Step9:Making More Difficult Cuts

The next step is to separate the manifold from the 90 degree entrance flowsplit. This must be done with the cutting plane operation, but will require use of some advanced features of that operation. The goal is simple, cut off the top flowsplit section without cutting through the manifold itself.

step 10: Dividing a Large Volume into Smaller Sections (Manual Discretization)

1. The only mesh shape left to be converted is the manifold section. Rather than converting the entire thing into a flowsplit, we want to manually divide it to get better resolution and accuracy in the GT-SUITE flow model. Manual discretization involves making cuts to divide up the large mesh shape into smaller mesh shapes and converting those into flowsplits.

2. In our case each end of the manifold has a runner connection. Since the center inlet is wide enough to cover both middle runners, the center section of the manifold should cover both middle runners. That means we want to divide the entire manifold into 3 sections; a center section and 2 end sections.

                         

 

 

Step11: 2.15Adding Flow Connections

1. You will notice that during the process of converting meshes to components, we created several pipes which do not align perfectly. To remedy this, we can use the flow connection operation to join the runner sections at the top of the manifold. To do this, select Flow Connection > Flow Connection from the Connections group under the tab Flow.

2. This will show available surfaces for adding flow connections, as shown below. To join the runners together, click on the flow connection face at the end of the first intake runner, then click on the flow connection face at the end of the second intake runner.

Extrude flow connection

To add a flow connection while preserving the geometry that we have displayed in GEM3D, we can add an Extruded Connection. To do this, select Extruded Connection from the Connections group in the Flow tab

                 

Step12: Discretizing the Model

1.Now that the model consists entirely of flow components, we can discretize the model. First, save the model again using the save toolbar button or choosing Home/Save. To discretize a model, select Export GT Model ( ) from either the Home tab or the toolbar. This will open the discretization window that contains the available discretization options.

GT-ISE Model

                                            

GT-ISE Model

 

 

Overall conclusion

1. Disecretization length affected on simulation time  & perforamnce parameters.

           1. for Disecretization length 0.1mm  Brake Torque is 0.31% less

           2. for Disecretization length 0.1mm  BSFC is 0.29% more

           3. for Disecretization length 0.1mm Max cylinder Pressure is 1.67% Less

           4. for Disecretization length 0.1mm simulation time is 12.7% more

2. Sucessfully discretize the Intake manifold by use of GEM3D

3.Took hands on experience of conversion of 3D model in to 1D - model.

4. Understood importance of discretization in GT-SUITE