GEM3D and Discretization

AIM

• 1. Tutorial- single cyl DI add case 2 with discretization length 0.1 mm for intake runner and compare with a default case.
  1. Parameters-Torque, BSFC, max cylinder pressure
  2. simulation time

• Explore tutorial no 2 (GEM3D) - “Building intake manifold from STL model”.

CASE 1

Introduction

A CI engine is an engine in which the fuel charge is ignited by the heat of compression. In a CI engine, the air is let into the combustion chamber and compressed to very high pressure. CI engine has a high compression ratio and a large amount of air to fuel ratio.

The CI engine model is shown below, consists of all required geometry :

CASE SETUP

The given problem involves running the solution at two different discretization length setup :

RESULT

TABEL SUMMARY

There not much difference between the result of both discretization length results. The discretization length of lower values gives the lower values compared to normal case setup.

But the difference between both results can be seen from the simulation time which we get while running the simulation. As from the given graph, we can see that the case setup 2, required more simulation time.

CASE 2

GEM3D is a 3D graphical pre-processor that combines building and importing tools used to create 1D GT-Suite models from 3D geometries. GEM3D can be used to build models from primitive components like pipes, flow splits, shells, catalysts, pumps, etc.GEM3D can also be used to import 3D CAD models from other applications, especially GT Spaceclaim. Once imported it can be used as a “characterizer” to automatically find effective lengths, diameters, bends, volumes, etc. of complex shapes, and convert them into GT-Suite equivalent parts, such as pipes and flow splits.

For our purpose, we are going to model intake manifold here. The first step is to import the intake manifold from an STL file in GEM3D, through the option provided to import 3D file.

GEM3D will create a mesh shape component ('GEMMeshShape') from the imported shape and add it to the model.

Next, we need to remove the intake and runner caps so the ends are open and available for flow, this can be done by using the separate by curves option. This will separate the geometry into parts based on changes in the surface of the object.

We obtain a separated intake manifold as shown in the screenshot below.

Now that the end sections of the runners and plenum are separated from the main shape, we can delete them from the model. After deleting this we are going to use the cutting plane to separate thee, 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. To enable the cutting plane, select 3 Points Cutting Plane from this group.

After that we will separate the components :

After that, we will separate the section into the flow components. After selecting the parts we will select Convert Shape to Component. This will open the convert mesh window.

Since this particular shape is a pipe, select Pipe. Click next. Select Multiple Bends since it has more than 1 bend.

Since we made the cut near the manifold where there is a smooth transition into the runner (fillets), the diameter at the end of the pipe is not really appropriate.

We have chosen a custom plane for Port 1, to define the diameter for the pipe.

We have chosen the diameter to be 48.6 mm. And also Confirm that the Wall Thickness is set to 1 mm in the Geometry tab of the Calculated Geometry window and press Next again.

In the Name and Simulation Attributes window, give the pipe a name of "run1-1". All the geometry is calculated during conversion, but some of the attributes on the main tab still need to be specified. Go to the main tab and type init for the Initial State Name. We can define the initial state directly in GEM3D by double-clicking on the name "init". This will open a 'FluidInitialState' template where we can define the Pressure as 1 bar and the Temperature as 300 K. We can get the properties of air from the template library by right-clicking in the cell for Composition and choosing value selector.

After that press the Finish button at the bottom of the conversion window to save the part.

Repeat the above procedures and convert the first section (next to the manifold) of the other 3 runners into flow components

After that the model looks like this :

Next, we need to convert the end sections of each runner into components.
Select the end section of the first runner and select Convert Shape to Component. This will open the convert mesh window, shown in the image below.

Select bent pipe so the inlet and outlet diameters can be different. Therefore, select the Multiple Bends option as bend type. Port 2 is fine and select define from port 1.

Check Wall Thickness is set to 1 mm and then click Next, give the component a name. All values are input from the last conversion. Since this component is still part of the intake runner, all of those attribute values are fine. Press the OK button at the bottom of the conversion window to save the part.

Repeat the same for all other ends after that the geometry should look like this :

After that, we need to add Custom Connection. To add a custom orifice to a flow component right-click on the first section of runner 1 and choose Add Connection. This will open the port connection window. In which we will have to define the parameters.

To account for the curved entry we want to modify the forward discharge coefficient. Since all 4 runners likely have the same curved entry shape, they should all get the same discharge coefficient. Therefore, define a parameter named [runner-cd] for the Forward Discharge Coefficient attribute.

Repeat the above procedure for the rest of the runners using connection names.

The next thing we need to specify the inlet and outlet or flow direction for the intake manifold.
To add the subassembly connection right-click on the end section of the first runner component and choose Add Connection. Set a Port ID of 1. Set the Flow Direction to "Outlet" since we expect the flow to be from the manifold through the runner and out of this port. Repeat this procedure for the rest of the runners.

NOw we will convert 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. We will use Cutting Planes to cut the part in two.

The next step is to convert both of these sections into flow components.

First, we will convert the D-shaped section by selecting Convert Shape to Component. In the convert mesh window that opens choose the Pipe option. Change the inlet and outlet port. Next, We will model this section as a Straight pipe. Press Next again and give it a name and click Finish to save the pipe.

After that, we will convert the next part of the pipe as a straight component.

After that, we will model the entrance to the manifold is separated. To do this, right-click it and select Convert Shape to Component.

Select Flowsplit from the select the conversion geometry options on the right side. And also change ports for desirable input. Now that we have selected the component type and identified the ports, click Next. Click on Next again and flow split using the exact geometry of the mesh shape will be created and drawn in the graphical window for comparison. The converted component is shown at the bottom.

The only mesh shape left to be converted is the manifold section which is used to convert the large volume into the smaller section. Rather than converting the entire thing into a flow split, we want to manually divide it to get better resolution and accuracy.

The first step is to use a cutting plane to cut off the first end section toward the first runner. Enable the cutting plane by selecting 3 Points Cutting Plane from the Cutting Planes group in the Convert tab. Select 3 points on the end of the manifold such that they form a plane nearly perpendicular to the manifold section.

After that, it will be used to divide the part into three parts, and model as flow split as separate components.

After creating the flow components, the intake manifold is look like this :

Now we will add flow connection, to join several pipes that do not align perfectly. To do this, select Flow Connection > Flow Connection from the Connections group under the tab Flow. 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. The sections should join together.

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. All the faces which are available for adding extruded connections appear, just as with flow connections.

When we are finished creating extruded connections, the model should look like this :

Discretizing the Model

Now that the model consists entirely of flow components, we can discretize the model.

To discretize a model, select the Export GT Model from either the Home tab or the toolbar. This will open the discretization window that contains the available discretization options:

We have used a discretization length of 40 mm and the output file name is "IntMan.gtsub". Once these are correct, we need to choose an orientation for the model. When GEM3D discretizes the model, it will need to place each component on a 2D map in GTISE. It will do this based on the current graphical orientation of the model by trying to match the parts placement.

Once the model is in this orientation, click the Discretize button and GEM3D will create a GT-SUITE model file (.gtsub). We will get a message saying the discretization completed successfully.

After that Pressing the Open in GTise button to open the newly created model file in GT-ISE. The model file map will look like the image below. This will be our final output:

Conclusion

• A single-cylinder diesel injection model with different discretization length has been successfully performed.
• We can see that by decreasing discretization length simulation run time increases.
• The intake manifold model for 1D simulation has been successfully created in GM3D.