fluent ic tut 01 hybrid approach

Tutorial: IC Simulation for Canted Valve Engine Using

Hybrid Approach

Introduction

Two approaches are employed in ANSYS FLUENT to solve in-cylinder (IC) problems,namely, hybrid approach and layering approach. The layering approach is used for en-gines with vertical valves like most diesel engines, while the hybrid approach is typicallyused for engines with canted valves like most spark ignited (SI) engines.

For either approach mentioned above, IC problems solved in ANSYS FLUENT consist ofthree stages.

1. Decompose the geometry into different zones and mesh them properly. By breaking upthe model into different zones, it is possible to apply different mesh motion strategiesto different regions in a single simulation.

2. Set up the engine case in ANSYS FLUENT with the help of a setup journal.

3. Perform a transient IC simulation.

In this tutorial setup and simulation process is explained for the hybrid approach. A similartutorial, IC Simulation for Vertical Valve Engine Using Layering Approach, exists for thelayering approach.

This tutorial demonstrates:

1. Procedure to setup IC flow problem using journal file: The journal file automaticallysets up the necessary motions for valves and piston, along with solution parameterwhich suit the IC simulation best. Journal file allows you to set up an IC simulationwith all the best practices built-in, without learning the dynamic mesh capability.This is made possible through the correct decomposition and zone name matching.Appendix A contains a sketch of the decomposition and the corresponding zone names.

2. Procedure to solve the cold flow simulation: This tutorial makes use of a In-CylinderOutput Controls to calculate swirl and tumble ratio.

c© ANSYS, Inc. April 22, 2011 1

Tutorial: IC Simulation for Canted Valve Engine Using Hybrid Approach

The limitations of the journal are:

1. The journal is applicable only for ANSYS FLUENT.

2. The journal cannot be used for 2D geometry.

The journal can automatically set up the following for an IC case:

1. All necessary dynamic zones for the valve motion.

2. All necessary dynamic zones for the piston motion.

3. Boundary conditions for all interior and interface zones related to valves or pistonmotion but NOT inlets, outlets, symmetry, or combustion models etc.

4. All solver settings in first order. You may need to change it to second order for greateraccuracy.

5. Events to open and close valves.

6. Events to change the under-relaxation factors (URF)s.

7. Events to change the time step size.

8. Solver parameters based on experience of the engineers at ANSYS FLUENT.

Note: Due to different file format between Windows and UNIX, if you use UNIX you mayneed to use dos2unix or dos2ux command to change the format for all *.scm and*.par files that come with the tutorial. You could also try to use a text editor to openthe files and then save it. Otherwise, you may not be able to load the scheme file andthe *.par file may not read correctly.

Prerequisites

This tutorial is written with the assumption that you have completed Tutorial 1, and thatyou are familiar with the ANSYS FLUENT navigation pane and menu structure. Some stepsin the setup and solution procedure will not be shown explicitly.

Problem Description

This tutorial considers a 3D symmetric geometry of a IC engine cylinder configuration.Case setup is performed using a scheme file that automatically sets up necessary motionsfor valves and pistons along with solution parameters found to be best suit for the in-cylindersimulation.

2 c© ANSYS, Inc. April 22, 2011


Figure 1: Geometry Decomposition

Setup and Solution

Preparation

1. Copy the files, (IC tutorial II.msh.gz. valve.prof, R 13 IC scheme-set-4.scm,and IC-motion-parameters.par) to your working folder.

2. Use FLUENT Launcher to start the (3D) version of ANSYS FLUENT.

For more information about FLUENT Launcher refer to Section 1.1.2 in the ANSYSFLUENT 13.0 User’s Guide.

3. Enable Double-Precision in the Display Options list.

4. Click the Environment tab and ensure that Setup Compilation Environment for UDF isenabled.

The path to the .bat file which is required to compile the UDF will be displayed assoon as you enable Setup Compilation Environment for UDF.

If the Environment tab does not appear in the FLUENT Launcher dialog box by default,click the Show More Options button to view the additional settings.

Note: The Display Options are enabled by default. Therefore, after you read in themesh, it will be displayed in the embedded graphics window.



Step 1: Mesh

1. Read the mesh file, IC tutorial II.msh.gz.

File −→ Read −→Mesh...

As ANSYS FLUENT reads the mesh file, messages will appear in the console reportingthe progress of the conversion.

2. Rotate and zoom the display to obtain the view as shown in Figure 2

Figure 2: Mesh Display

Note: The case has a symmetric plane. Use of symmetry helps reduce cell count by a factorof two and thus greatly reduce the run time.

Layering is used for lower combustion chamber and the valve seat, to reduce cell countand to properly resolve the flow. Tetrahedral mesh is used in the upper combustionchamber and ports to facilitate the setup.

The mesh must have the correct decomposition and names before using the journalto automatically set up the case. Figure 1 shows the geometry decomposition. InAppendix A, a sketch of the decomposition and the corresponding names are providedfor quick reference.



Step 2: General Settings

1. Check the mesh.

General −→ Check

ANSYS FLUENT will perform various checks on the mesh and report the progress inthe console. Make sure that the minimum volume reported is a positive number.

Warnings will be displayed regarding unassigned interface zones, resulting in the failureof the mesh check. You do not need to take any action at this point, as this issue willbe rectified when you define the mesh interfaces in a later step.

2. Scale the mesh.

General −→ Scale...

Retain the default settings for this tutorial,as the mesh is already scaled properly. Butotherwise this is a very important step. Since the meshing parameters are determinedfrom the initial mesh, it is imperative to properly scale the mesh.

3. Read the valve profile file.

File −→ Read −→Profile...

(a) Select valve.prof from the Select File dialog box and click OK.

This file contains valve lift information. Refer to ANSYS FLUENT User’s Guidefor the format of this profile.

Note: The following message will appear after reading the profile. This means thattwo profiles, i.e., ex-valve and in-valve, have been read in. The profile nameswill be required for the valve setup at a later stage.

Reading profiles file...141 "ex-valve" point-profile points, angle, lift.140 "in-valve" point-profile points, angle, lift.

4. Load the scheme file.

File −→ Read −→Scheme...

(a) Select R 13 IC scheme-set-4.scm from the Select File dialog box and click OK.

5. IC setup.

Define −→ User-Defined −→In-Cylinder Mesh Motion Setup...



Note: The IC Setup dialog box contains some default values. You will not use theseparameters as they are problem dependent. Instead, you have to read a parameterfile.

(a) Click Read at the bottom of the dialog box and read the input parameter fileIC-motion-parameters.par.

The file contains all the engine parameters and parameters required for valvesmotion and piston motion setup. You could also enter the parameters directly inthe dialog box.

Note: You can use the Write button to write out the parameter files for lateruse. The IC-motion-parameters.par provided was written out by this aftermanually entering those numbers. The parameter file is text file that can beedited easily using any text editor. The parameters are put in the file in anorder that is similar to the dialog box.

(b) Click OK.

The journal will automatically set up mesh motion for the intake valve, exhaustvalve, and piston. This automation is achieved through correct decompositionand zone name matching. If the names of the zones are incorrect, the case willnot be setup and you will be notified about the zones for which the names are notmatched. The scheme file will automatically select Standard k-e as the turbulencemodel.

Note: The explanation of the parameters is in Appendix B. For this tutorial,piston type1 is used. More details on different type of pistons are explainedin Appendix C.



6. Examine the profile. See Figure 3.

(a) Enter the following command to display the valve profile:/define/dynamic-mesh/controls/icp/ppl ex-valve in-valve () 0 720 10y

Figure 3: IC Valve Profile

Note: In convention with ANSYS FLUENT, the 0 crank angle (CA) is at topdead center (TDC) after compression. So, at 0 CA both intake and exhaustvalves are closed as shown in Figure 3. If in your convention, 0 CA is atTDC after power stroke, you will need to shift your profile.



Step 3: Models

1. Specify the turbulence model.

Models −→ Viscous −→ Edit...

Journal will automatically select Standard k-epsilon turbulence model and use defaultvalues as shown in the dialog box.

2. Close the Viscous Model dialog box.



Step 4: Zone Motion Preview

Zone motion preview will translate moving zones, without solving any mesh or flow equa-tions. This helps to quickly check valve profile and axis definition, that you put into theIC Setup dialog box. If any of them is wrong, then your zone motion will not look correct.For instance, if you use (0 0 1) as your piston motion axis (which should be (0 1 0)), thenduring zone motion, the piston will move in the z direction instead of y direction.

1. Set up mesh display.

General −→ Display

2. Perform a zone motion preview.

Dynamic Mesh −→ Display Zone Motion...

(a) Click Integrate.

(b) Click Preview.

(c) Close the Zone Motion dialog box.



3. Write out a case file, IC tutorial II CA000.cas.gz

File −→ Write −→Case...

The mesh is at TDC, i.e., CA 0.

Step 5: Mesh Motion Preview

A full 720 degree of mesh motion may not be necessary. But it is necessary to move themesh to the simulation starting CA that is normally a few degrees before intake valve openat TDC. In this case, CA 344 is the starting point of the simulation because the intake valveopens at CA 349.

1. Perform a mesh motion preview.

Dynamic Mesh −→ Preview Mesh Motion...

(a) Enter 1396 for Number of Time Steps.

This amounts to 344 degrees. Since non-constant time step size is used, 1376 =(4X344) steps of mesh motion, corresponds only to 339 degrees.

(b) Enable from Options group box, Enable Autosave.

i. Enter 180 for Save Case File Every (Time Steps).

ii. Click OK to close the Autosave Case During Mesh Motion Preview dialog box.

Autosave helps identifying mesh motion problems if the mesh motion fails.



You can also enable Display Mesh and Save Picture, to save the pictures ofthe mesh at specified Display Frequency for creating a mesh motion animationlater.

(c) Click Apply.

(d) Click Preview.

Note: Mesh motion for this tutorial case takes about one hour on serial WindowsXP 3.19GHz machine.

(e) Close the Mesh Motion dialog box.

Step 6: Boundary Conditions

Boundary Conditions

1. Specify the inlet boundary conditions.

Boundary Conditions −→ inlet −→ Edit...

(a) Select Intensity and Hydraulic Diameter from the Specification Method drop-downlist in the Turbulence group box.

(b) Enter 5 % for Turbulent Intensity.

(c) Enter 0.03 m for the Hydraulic Diameter.

(d) Ensure that in the Thermal tab Total temperature is 300.

(e) Click OK to close the Pressure Inlet dialog box.

2. Specify the outlet boundary conditions.

Boundary Conditions −→ outlet −→ Edit...

(a) Select Intensity and Hydraulic Diameter from the Specification Method drop-downlist in the Turbulence group box.

(b) Enter 8 % for Backflow Turbulent Intensity.

(c) Enter 0.03 m for the Backflow Hydraulic Diameter.

(d) Ensure that in the Thermal tab Total temperature is 300.

(e) Click OK to close the Pressure Outlet dialog box.

3. Make sure the boundaries with name symm-(except symmetry-bowl) have symmetryboundary condition.

There is no need to specify boundary conditions for other face zones. Those will beautomatically setup by the scheme.

4. Write out a case file, IC tutorial II CA344.cas.gz.

File −→ Write −→Case...



Step 7: Dynamic Mesh

In the In-Cylinder Output Controls dialog box, you can specify various quantities neededfor the calculation of swirl and tumble along with the frequency of writing the output, tothe chosen file. Swirl is used to describe circulation about the cylinder axis. Tumble flowcirculates around an axis perpendicular to the cylinder axis, orthogonal to swirl flow.

Dynamic Mesh

1. Click on Settings... in Options group box.

2. In the Options dialog box click In-Cylinder tab.

3. Enable Write In-Cylinder Output and click Output Controls....

(a) In the In-Cylinder Output Controls dialog box, set In-Cylinder Data Write Frequencyto 1.

(b) Ensure center of gravity is selected from Swirl Center Method.

(c) From the Cell Zones list select fluid-ch and fluid-piston-layer.

(d) Set X, Y, Z from Swirl Axis to 0, 0, 1 respectively.

(e) Set X, Y, Z from Tumble X-Axis to 1, 0, 0 respectively.

(f) Set X, Y, Z from Tumble Y-Axis to 0, 1, 0 respectively.

(g) Enter ic-hybrid.txt for File Name.

(h) Click OK.



4. Click OK in the In-Cylinder Settings dialog box to close it.

Step 8: Solution

1. Initialize the flow.

Solution Initialization −→ Initialize

2. Create a velocity magnitude contour plot.

(a) Create an iso surface.

Surface −→Iso-Surface...

i. Select Mesh... and Y-Coordinate from the list of Surface of Constant.

ii. Enter 0.02 for Iso-Values.

iii. Enter y=.02 for New Surface Name.

iv. Click Compute and then Create.

v. Close the Iso-Surface dialog box.

(b) Check ID of iso surface.

Surface −→Manage...



In this case, it is 55. This ID will be needed later for contour plot.

(c) Display iso surface.

Graphics and Animations −→ Mesh −→ Set Up...

i. Deselect all from the list of Surfaces.

ii. Select y=.02 and click Display.

iii. Close the Mesh Display dialog box.

Figure 4: Iso Surface View



(d) Specify the view.

Graphics and Animations −→ Views...

i. Enter plot-view for Save Name.

ii. Click Save and close the Views dialog box.

(e) Display velocity magnitude contours.

Graphics and Animations −→ Contours −→ Set Up...

i. Enable Filled in the Options group box.

ii. Disable Auto Range and Clip to Range.

iii. Select Velocity and Velocity Magnitude from the Contours of drop-down list.

iv. Enter 0 for Min and 30 for Max.

v. Select y=.02 from the Surfaces list.

vi. Close the Contours dialog box.

Similar velocity contour plots will be saved during the simulation. The saved plotscan be used to create an animation.

3. Set up commands to save figures for animations.

Calculation Activities (Execute Commands)−→ Create/Edit...

(a) Set Defined Commands to 1.

(b) Enable Active.

(c) Set Every to 20.

(d) Select Time-Step from the drop-down list of When.

(e) Enter /dis/sw 1 /dis/set/cont/sur (y=.02) /dis/view/rv plot-view /dis/contvm 0 30 /dis/sp/vel %t.tiff for Command.



(f) Click OK.

Note: In the above command instead of y=.02, the surface ID for surface y=.02 canbe used. The ID for this surface is 55. This can be different on different systems.

You could create other contour plots using similar steps.

4. Set the time step parameters for calculations.

Calculation Activities

(a) Enter 180 for Autosave Every (Time Steps).

(b) Click Edit....

i. Enter ./IC tutorial II CA344.gz for File Name.

ii. Click OK to close the Autosave dialog box.

In the Autosave dialog box, IC tutorial II CA344 .gz is used as the filename.The number of time steps will be appended to it. So, at time step 180, a case/data,IC tutorial II CA344 0180.cas/dat.gz will be automatically saved.

Note: If greater accuracy is desired, change to Second Order Upwind discretization

Solution Methods

5. Write out a case and data file, IC tutorial II CA344 0000.cas.gz

File −→ Write −→Case & Data...

6. Run the simulation for the 1440 time steps.

This will complete half cycle of the cylinder. If you require, you can run for 2880 timesteps to observe the full cycle.

Run Calculation

Step 9: Postprocessing

At the end of the simulation you will have the following files:

1. Tiff files for velocity magnitude.

2. Auto-saved case and data files.

3. A text file ic-hybrid.txt,containing swirl, x-tumble, y-tumble, and moment of inertiaas a function of CA.

For more information refer to section 11.6.3 In-Cylinder Settings, in the ANSYS FLU-ENT User’s Guide.



Figure 5: CA = 379(deg) Figure 5: CA = 424 (deg)





Figure 6: CA = 644 (deg) Figure 6: CA = 689 (deg)

Summary

In this tutorial you have learned how to setup an IC engine cold flow case in ANSYSFLUENT. Scheme file provided with this tutorial can be used for setting up case on anyother IC engine geometry, provided mesh and name of boundary and cell zones are createdas per specification in the Appendix A.

Appendix A

Figure 7: Sketch of Decomposition and Zone Names



No. Fluid Zone Name Mesh Requirement1 fluid-ch tet mesh2 fluid-rootname-ib layered mesh3 fluid-rootname-port any mesh4 fluid-rootname-vlayer layered mesh5 fluid-piston-layer layered mesh

Figure 8: Boundary Zones



No. Boundary Zone Name1 intf-int-rootname-ib-fluid-ib

2 intf-int-rootname-ib-fluid-port

3 intf-int-rootname-ob-fluid-vlayer

4 intf-int-rootname-ob-fluid-port

5 intf-rootname-ib-fluid-ib

6 intf-rootname-ib-fluid-ob-quad

7 intf-rootname-ib-fluid-ob-tri

8 intf-rootname-ob-fluid-ch

9 intf-rootname-ob-fluid-vlayer

10 seat-rootname

11 rootname-ch

12 rootname-ib

13 rootname-ob

14 int-piston

15 cyl-tri

16 piston

Appendix B

Parameters in the IC Setup dialog box.

1. Input parameters under Engine Parameters tab:

Crank Shaft Speed: Engine RPM.

Crank Angle Step Size: Time step size in terms of CA.

Piston stroke: Piston Stroke and Connecting Rod Length, together control the pistonmotion.

Connecting Rod Length: Piston Stroke and Connecting Rod Length, together controlthe piston motion.

Minimum Valve Lift: Closest gap from valve and valve seat.

Symmetry Engine: Use this option if one has a symmetry engine like the demo.

Point on Symmetry: Point on Symmetry and Symmetry Normal together define a planefor nodes projection.

Symmetry Normal: Point on Symmetry and Symmetry Normal together define a planefor nodes projection.

Cylinder axis origin and cylinder axis direction together define a cylinder for theengine cylinder. ANSYS FLUENT needs this to project nodes on the engine cylinderback to a perfect cylinder.

2. Input Parameters under Piston Motion Setup tab:

Meshing Strategy Hybrid Approach: This approach is used for canted valve engine.Three different piston mesh types can be modeled under Hybrid Approach.



Layering Approach: This approach is used for the vertical valve engine. There aretwo mesh types (conformal and non-conformal mesh type) used for layeringapproach. For further details please refer IC tutorial I-B.

Piston Type: There are three piston types. For pistons with enough room to putone layer to start with, select 1. For flat pistons with tight squish combustionchamber and thus insert-boundary-layer is used, select 2. For complex piston shapelike GDI engines and thus insert-interior-layer is used, select 3. The decompositionfor different piston types is different. Appendix C explains difference betweenthese piston types.

Piston Stroke Cutoff: Parameter used to control the height of upper remeshing com-bustion chamber. The rule of thumb is to use max valve lift plus 4 or 5mm.

Cylinder Radius: Cylinder radius.

Cylinder Axis Direction: Cylinder Axis Origin and Cylinder Axis Direction together definea cylinder for the engine cylinder. ANSYS FLUENT needs this to project nodeson the engine cylinder back to a perfect cylinder.

Cylinder Axis Origin: Cylinder Axis Origin and Cylinder Axis Direction together define acylinder for the engine cylinder. ANSYS FLUENT needs this to project nodes onthe engine cylinder back to a perfect cylinder.

3. Input parameters under Valve Motion Setup tab:

Number of Valves: The total number of vales in the engine.

Valve Number: Valve number for which parameters are setup.

For example, if there are total 4 valves, valve number parameter will vary from1 to 4. The parameters like Valve Name, Valve Profile Name, etc., are required tosetup for each valve number and these parameters are stored against the valvenumber.

Valve Name: The auto set up is done through name matching system. This is thevalve root name.

Valve Profile Name: Valve profile is used to define valve motion. This name is shownup on ANSYS FLUENT screen during the step of Read the Valve Profile.

Open Valve: CA to open the valve. At the specified CA, the valve will open by formingthe non-conformal interface.

Close Valve: CA to close the valve. At the specified CA, the valve will close by deletingthe non-conformal interface.

Refer Appendix D for the recommended practice to select the opening and closingcrank angles.

Valve Margin Radius: Valve radius.

Valve Axis Direction: Valve Axis Origin and Valve Axis Direction together define a cylin-der for the valve. ANSYS FLUENT needs this to project nodes back to a perfectcylinder.

Valve Axis Origin: Valve Axis Origin and Valve Axis Direction together define a cylinderfor the valve. ANSYS FLUENT needs this to project nodes back to a perfectcylinder.



Variable URFs: With this option enabled, the URFs are not a constant. When valvesare opening or closing, the URFs for k, e, Momentum, and Pressure will beautomatically reduced and later on switched back.

Variable Crank Angle Step Size: With this option enabled, the time step size is not aconstant. When valves are opening or closing, the time step size will be auto-matically reduced and later on switched back.

Duration: The duration for reduced URFs or/and time step size.

Appendix C

Different types of piston and treatment

Piston shape can vary from flat piston seen in some spark ignited (SI) engines to verycomplex piston bowl shape seen in some diesel or GDI engines. This physical differencemakes it necessary to treat different pistons in different ways. In ANSYS FLUENT alldifferent pistons can be categorized into three different types.

1. Piston type 1 is designated for engines with enough squish volume to put one layerof wedge elements when the piston is at the TDC, be it a flat piston or piston with abowl, as shown in Figure 9. The figure also shows the names required. Note that forthe geometry with a bowl, piston should also include the bowl.

Figure 9: Piston Type 1 Decomposition and Zone Names



The mesh requirement is shown in Figure 10. A layer of wedge elements is neededfor layering for piston type 1. In most cases, you can not put a layer of hex meshbecause the squish volume in typical engines would not allow for extra pyramids ontop of int-piston needed to make the transition from hex mesh to tet mesh. If yourengine has large squish volume to allow for pyramids and thus using hex vs. wedges,contact your support engineer.

Figure 10: Piston Type 1 Mesh Requirement



2. Piston type 2 is designated for engines without enough squish volume to put onelayer of wedge elements when the piston is at TDC, be it a flat piston or piston witha bowl, as shown in Figure 11. The figure also shows the names required.


The mesh requirement is shown in Figure 12.

With piston type 2 you have the choice to include a bowl. This option is in the ICSetup dialog box. For piston type 2, a layer of wedge elements is not needed. Instead,ANSYS FLUENT will automatically create a layer at specified CA. The two CAs forIntake Stroke and Power Stroke are specified in the IC Setup dialog box.



Piston type 1 and 2 do not allow the valves to penetrate into the bowl because thevalves will interfere with either int-piston for piston type 1 or piston for piston type 2.

3. Piston type 3 is designated for engines with such valve penetration. Figure 13 showsthe names required.


The mesh requirement is shown in Figure 14.


For piston type 3, a layer of wedge elements is not needed. Instead, ANSYS FLUENTwill automatically create a layer at user specified CA in the IC Setup dialog box. Thereis only one insert CA for piston type 3. The same angle is used for both power strokeand intake stroke. Insert location uses Cylinder Axis Origin.



Piston type 1 and 2 are commonly used for diesel and gasoline engines. Piston type 3could be used for some GDI engines with deep valve penetration. Piston type 3 is the mostgeneral and requires less decomposition. However, it has less number of layered elementsand utilizes more tet cells and thus typically has more cells and takes more computationaltime. If possible, you should always try to use piston type 1 or 2.

The mesh files for all the above piston types are provided with this tutorial. You will needto do the following to see the results.

1. Read the mesh file and the profile.

2. Load the scheme file.

3. Read the parameter file in through the IC Setup dialog box. This will set up thepiston. Make the required changes in the Piston Motion Setup.

4. Perform Steps 3 through Step 9 of this tutorial.



Appendix D

Determining the valve opening and closing angles

In Valve Motion Setup in IC Setup dialog box, you need to specify the opening and closingCA of each valve. It should be specified in such a way that the flow to the chamber shouldneither be under predicted nor over predicted. If we specify the actual valve opening CAin the setup this will allow too much of flow into the chamber as there is a minimum liftfor the valve due to the V-layer modeled in the geometry decomposition. To overcome this,one can adopt the following approach in setting up the valve parameters.

Typical valve profile will be as shown below. As per profile valve opens at 350 deg CA andat about 358 deg CA the valve lift reaches 0.1 mm

((in-valve point 140 1)(angle3.500000e+02 3.515000e+02 3.530000e+02 3.545000e+02 3.560000e+023.5750000e+02 ..............)(lift1.000000e-07 1.130000e-06 3.848000e-05 5.565000e-05 1.010000e-041.090000e-04 ................))

While modeling, IC case in ANSYS FLUENT we usually keep the V-layer thickness to 0.1mm.

Figure 15: Valve Motion in Actual Engine and Simulation



• If valve opens at 350 deg CA, as per profile and in practice flow will vary accordingto the lift profile in Figure 16.

Figure 16: Actual Valve Opening Profile

• If the valve opening CA is set as 350 degrees in ANSYS FLUENT the simulated valvelift profile will be as shown in Figure 17 and the flow will be over predicted.

Figure 17: Valve Opened at CA 350 in ANSYS FLUENT



• If the valve opening CA is set as 356 in ANSYS FLUENT the simulated valve liftprofile will be as shown in Figure 18 and the flow will be under predicted.


• So the recommended practice is to keep the valve opening CA at the average of boththe above which is CA 353. The simulated valve lift profile is as shown in Figure 19and this will provide the flow rate approximately equal to the actual flow rate.


The same approach is used in determining valve closing CA.


fluent ic tut 01 hybrid approach

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