Discretization of a Plenum using GEM3D

1. Tutorial - single cyl DI add case 2 with discretization length 0.1 mm for intake runner and compare with default case

• Parameters-Torque, BSFC, max cylinder pressure
• Simulation time

Let's open the model of the tutorial section of GTP:

The map of the model is shown below:

It's a CI, single-cylinder engine, with two pipes for the intake system and the other two pipes for the exhaust system., SOHC, and direct-injection, naturally aspirated. The heat transfer model is the Woshni GT, and the cylinder geometry is shown below:

Let's explore the Case setup:

At the beginning only case 1 was defined. To complete the challenge, the discretization length of the intake_runner was transformed into a parameter and another case was added, choosing a value of 0.1.

Let's analyze the results of the simulations.

It's clearly visible that the difference between the two cases in terms of Brake torque and BSFC is very small.

Even the difference of the maximum cylinder pressure is quite small:

But let's compare the factor of real-time:

it's clearly visible that the second case is a bit accurate but it requires a lot more time than case 1. This is even visible from the cumulative computational time:

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

Let's explore the cited tutorial.

After opening GEM3D and clicking on "import 3d" on the toolbar, the plenum file is selected, with the following radio buttons selected:

Showing the following 3d element:

Let's transform this 3d part into a GTP model.

STEP1:

The inlet and the ends of the intake manifolds are closed. So it's necessary to erase these parts to allow the movement of the fluid through the element. For this reason into "Convert tab" is used the command "Separate by curves", which divides the element into different sub-parts, based on changes in element geometry, using a tolerance of 1.0:

Now, is possible to erase the parts that block the movement of the fluid:

STEP 2

Now is possible to divide the 3d model into sub-volumes that will be discretized into GTP. Let's start dividing the plenum from the pipes.

Into "convert" tab there is the command "3 points cutting planes" that allows choosing three points on the surface of the model and creating a plane, that cuts the geometry:

At the end of this operation, the plenum has been divided from the pipes.

STEP 3

Now that the pipes are divided from the plenum, it is possible to define their rule into the GTP model, so it's possible to convert them into a flow component. Right-clicking on the 3d part and selecting "Convert the shape to component", this window appears:

Two ports are required for a pipe: port 1 for the inlet and port 2 for the outlet. It is necessary to choose accurately the ports. On the right is possible to define the flow component in which it will be transformed.

For this application, it is a pipe.

On the left, into Geometry definition, the bend type is set on multiple bends and a linear interpolation between bends. On the right, for port 1, into "measurement location" a "custom plane" is chosen and into "shape" tab a "user-defined diameter: 48.6" is even chosen. For port 2, "define from port 1" is set, to define that the outlet port has the same dimension of the inlet port. Below there is "show entire model" that allows to see the entire model and how the ports are linked to the entire model.

A wall thickness of 1mm is chosen, in the following page:

Then the "initial state name is chosen":

And a wall temperature of 300 K is set:

After that the first element is complete. The same passages are repeated for the other runners.

After all the passages are complete, the model will be as shown below:

Now it's necessary to repeat the same passages for the pipes at the end of the intake system, obtaining, in the end, the following model:

There are some extra surfaces between the pipes, created after using "separate by curves", that must be deleted:

STEP 4

Cutting the plenum, to divide the pipes from it, the right connection was lost. In fact, the curved connection allows the flow to enter better into the pipes. For this reason, a custom connection is added:

right-clicking on the pipes, selecting "add connection", the following window appears:

Into "case setup" this value is set on: 0.95.

STEP 5

The next thing to do is to set the end connection, to define the movement of the flow. So right-clicking on the last pipes of the model, choosing "add connection" as shown below:

And these passages are repeated for every pipe.

STEP 6

Now it's necessary to divide into smaller parts the plenum, that has parts with variable geometry.

Using the command "Pipe normal cutting plane", a plane normal to the pipe is created:

This is how the 3d model appears after the passages:

Now every single shape must be converted into a flow component. Right-clicking on every part, and choosing the command "convert shape to component" is possible to transform every shape defined of the plenum:

STEP 6

During the conversion is possible to notice that are elements not perfectly linked to the others. For this reason is necessary to correctly define these connections:

For the pipes that are not perfectly linked to the plenum the "extruded connection" is used, to add a flow connection between the plenum and intake runner pipes, while preserving their geometry.

STEP 7

The last part of the tutorial is about the discretization of the model. Now that every single part has been defined as flow volume, is possible to discretize the model and using it on GTP, clicking on "Export GT Model":

Obtaining the following GTP model of the intake manifold: