Week 9: Project 1 - Surface preparation and Boundary Flagging (PFI)
In this project, a single-cylinder Port-fuel-injection (PFI) engine is setup for no-hydro simulation. Prior to it, surface preparation and boundary flagging are performed to make the geometry free from errors and to allocate the boundaries and regions. No-hydro simulation is performed to check the mesh generation and correctness of movements in the geometry before we proceed for full hydrodynamic simulation.
Objectives:
Boundary Flagging and Extracting Regions
Surface Preparation
No-hydro case setup
Geometry:
The PFI geometry .stl file is imported in the Converge Studio. The base geometry has surface errors that need to be cleared before we move up with the simulation. Boundaries need to be flagged for creating the flow through the geometry and appropriated regions are extracted to initialize the flow and to create the events between the regions.
From the diagnosis, it can be observed that the following errors are detected with the surfaces viz., intersections, Nonmanifolds, open edges & overlapping, etc.
Boundary Flagging:
To flag the boundaries, we need to create the fences across the edges of separating boundaries so it eases in the selection of boundaries.
Liner:
Two edges were selected to mark the fence across the Liner edges and the boundary is flagged using the boundary fence method as shown below.
Piston:
The piston is flagged by the boundary fence method as shown below.
Cylinder Head:
Boundary fences are created along the 4 edges which separate the region of the ports & spark plug from the cylinder head region and the cylinder head is extracted as shown below.
Intake Port / Inflow:
The intake port is split into two boundaries & later into two regions to separate the boundaries for different initial and boundary conditions. The intake port is where fuel spray and the air is injected. A fence is created using a fence between vertices and appropriate boundaries are flagged from the boundary fence method.
Exhaust Port / Outflow:
The outflow is flagged using the boundary fence method and the rest of the region as outflow as shown below.
Valves:
Intake & Exhaust ports, Liner, and cylinder head are hidden and then valves are visible. The valve geometry is flagged into 3 boundaries. This is done to create the events and ease in the creation of disconnect triangles and to assign realistic boundary conditions. Also, a translatory motion is provided to these valves by loading the motion files.
Spark Plug & Terminal:
The region where the spark is generated is at a higher temperature than the rest of the spark plug. Hence, two boundaries are necessary to assign appropriate conditions.
Top of Valve top assigned to port boundaries:
Due to the translatory motion of the valves and as it is connected to ports, during movement of the surface of the ports gets distorted. To avoid this distortion, the top of the top valves is assigned to the port boundary as shown below.
Flagged boundaries:
All the flagged boundaries are as shown below.
Surface Preparation:
From the diagnosis, it can be observed that the following errors are detected with the surfaces viz., intersections, Nonmanifolds, open edges & overlapping, etc.
As can be seen from the picture above, there exist intersections between the intake ports and cylinder head this is due to the clash of the geometry of intake valves and cylinder head. To avoid this error, valves are translated by little amount.
Once the intersections are cleared, nonmanifold triangles are deleted and open edges are cleared by patching and stitching the adjacent triangles. Then appropriate normal orientations are transformed depending upon the fluid flow domain. The above actions make the geometry free from errors.
Regions:
Regions are created which are used to create events between the zones and to initialize the realistic initial conditions in the flow domain.
The figure below shows the boundaries assigned to thye respective regions.
Initial and boundary conditions:
Case parameters setup
Application type Crank angle-based IC engine
Physical Parameters Cylinder Bore: 0.086m
Stroke:0.09m
Connecting rod length: 0.18m
Crank speed:3000rpm
Gas Simulation Reaction Mechanism Therm.dat uploaded
Mech.dat uploaded
Run Parameters Solver-Transient
Type-Crank angle-based engine simulation
Simulation mode - no hydro
Simulation Time Start time:-480 deg
parameters End time: 240deg
Solver Parameters Solver scheme:PISO
Type: Density-based
Boundary conditions:
Piston Boundary Type-Wall
Wall motion - Translating
Surface Movement -Moving
Law of wall (Piston Motion)
Temperature - 450k(Law of Wall)
Boundary Type -Wall
Wall motion -Stationary
Liner Surface Movement -Fixed
Law of wall
Temperature - 450k(Law of Wall)
Cylinder Head Boundary Type -Wall
Wall motion - Stationary
Surface movement - Fixed
law of wall
Temperature - 450k (law of wall)
Exhaust port Boundary type - wall
Wall motion - Stationary
Surface Movement - Fixed
Law of wall
Temperature-500k (law of wall)
Intaje Port1 Boundary type - wall
Wall motion - Stationary
Surface Movement - Fixed
Law of wall
Temperature -425k
Intake Port2 Boundary Type - Wall
Wall motion - Stationary
Surface Movement - Fixed
Law of Wall
Temperature - 425K
Spark Plug Boundary Type - Wall
Wall motion - Stationary
Surface Movement - Fixed
Law of Wall
Temperature - 550K
Spark Plug Terminal Boundary Type - Wall
Wall motion - Stationary
Surface Movement - Fixed
Law of Wall
Temperature - 600K
Intake Valve Boundary Type - Wall
Wall motion - Translating
Surface Movement - Moving
Law of Wall
Temperature - 480K
Profile - loaded
Minimum Lift - 2e-4m
Exhaust Valve Boundary Type - Wall
Wall motion - Translating
Surface Movement - Moving
Law of Wall
Temperature - 525K
Profile - loaded
Minimum Lift - 2e-4m
Inflow Boundary Type - Inflow
Temperature- 363K
Pressure - 101325 Pa
Species - Air
Outflow Boundary Type - Outflow
Temperature- 800K
Pressure - 101325 Pa
Species - CO2 - 0.192304
H20 - 0.088559
N2 - 0.719137
Regions:
Cylinder Region Temperature - 1360K
Pressure - 185731 Pa
Species - CO2 - 0.192304
H20 - 0.088559
N2 - 0.719137
Intake Port 1 Temperature - 390K
Pressure - 101325Pa
Species IC8H18 - 0.025508
O2 - 0.20157
N2 - 0.77292
Intake Port 2 Temperature - 370K
Pressure - 101325Pa
Species - Air
Exhaust Region Temperature - 1360K
Pressure - 185731 Pa
Species - CO2 - 0.192304
H20 - 0.088559
N2 - 0.719137
Events:
Cyclic Between Cylinder region & Intake Port 1, Period -720 deg, Event - Valve
Between Cylinder region & Exhaust Region, Period -720 deg, Event - Valve
Permanent Between Intake Port 1 & Intake Port 2, Event -Open
Mesh Size:
Here the base grid of 0.004m is used along with the fixed embedding. For the Intake and Exhaust valve angle scale of 3 and 1 embedding layer is used with Permanent Mode. Whereas, for the Cylinder region and zones next to the valves in the ports a cylinder entity is used with a scale of 2 & 1, respectively.
Results:
The results are processed for No-Hydro simulation and the grid size is coarsened by a factor of 4 (n = -2) as the computation time was too high for the fine mesh. Grid was coarsened as it was only a no-hydro simulation. The simulation took 263 sec while running it with 6 processors.