Converge Capability

8/18/2019 Converge Capability

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Computational Engineering India Pvt. Ltd., Office #4, Aditya Shagun Mall, Bavdhan, NDA-Pashan

Road, Pune 411021 Phone +91 20 66521610

Copyright CEI, India 2012

CONVERGE – Features, Capabilities and Applications

CONVERGE™

CONVERGE™ – The industry leading CFD code for complex geometries with moving

boundaries.Start using CONVERGE™ and never make a CFD mesh again.

CONVERGE™ is a revolutionary CFD code that eliminates the grid generation bottleneck

from the simulation process, developed for both, high productivity and high accuracy.

Learn How CONVERGE™ Can Simultaneously Increase Productivity and Accuracy

Written by engine simulation experts to address the deficiencies of other CFD codes.

Uses runtime grid generation so the user spends no time creating grids.

Moving boundaries are as easy to include in simulations as stationary boundaries. As

a result, including moving valves, for example, does not add any additional setup

time. Uses a structured, Cartesian mesh for increased accuracy.

Allows for very easy grid resolution studies, which can be critical for obtaining

accurate results.

The actual geometry information is stored so that increased resolution at boundaries

results in a more accurate geometric representation. In other words, no geometric

features are lost from the original surface definition as output from CAD.

Transient "grid scale" feature can be used to automatically scale the entire grid on-

the-fly or at pre-determined times. This is very useful, for example, during the

compression portion of the cycle where decreased resolution may be adequate.

Fixed grid embedding can be used to add resolution where necessary, such as nearnozzles or boundaries. This fixed embedding can be activated and deactivated at any

time in the simulation.

Adaptive Mesh Refinement (AMR) can be applied to the velocity field and/or any

scalar field (e.g., temperature) to automatically increase resolution where needed. A

maximum number of cells can be specified by the user to keep runtimes reasonable.

In this case, the AMR algorithm will prioritize and add resolution where it is needed

most.

The SAGE detailed chemistry solver is included for no extra charge. This allows users

to include detailed chemistry in their calculations in a very cost-effective way.

Advanced sub-models for sprays, wall film, turbulence, ignition, combustion andemissions are included.

Fully parallelized with automatic domain decomposition and excellent speedup.

One CFD code can be used for all of your IC engine applications. There is no need to

"map" between different codes or use different codes for different types of IC

engines.

Problem

Traditional CFD gridding techniques typically have five major issues that lead to increased

project budgets and reduced solution accuracy:

A large amount of time is needed to create the initial grid.


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Moving boundaries can significantly increase the complexity and required time to

generate the grid and handle the mesh motion.

Traditional moving methods continually deform the mesh leading to numerical

inaccuracies.

Non-orthogonal cells result in numerical inaccuracies and complex numerics.

Once the grid is created, the geometry representation is only as accurate as the

mesh resolution allows.

Solution

CONVERGE™ solves the problems described above by employing a runtime grid generation

technique with the following features:

Eliminates the user-time to generate grids - only the surface geometry is supplied to

the CONVERGE™ solver.

Allows moving boundaries to be handled completely automatically.

Eliminates the deforming mesh issues typically associated with moving boundaries.

Allows for perfectly orthogonal cells resulting in improved accuracy and simplified

numerics.

Maintains the true geometry, independent of the mesh resolution. Therefore, the

use of fixed embedding or adaptive mesh resolution on boundaries increases the

accuracy of the geometry representation.

Development Motivation

CONVERGE™ was developed with two goals

• Increase productivity

• Increase accuracy

Historically, meshing issues have been the limiting bottleneck for both accuracy and

productivity.

Extensive technologies are available in CONVERGE™ with the goal of placing cells only when

and where they are needed to minimize run times and grid dependencies

• Adaptive mesh refinement (AMR) to add cells based upon gradients in field variables

• Grid embedding to add resolution in key areas

CONVERGE™ has a rich set of physical models available for turbulence, spray and

combustion to model any engine type (Diesel, natural gas, dual fuel, port fuel injected,

prechamber, HCCI, direct injected, etc)• CONVERGE™ runs great in parallel

• CONVERGE™ was written from scratch and is not based upon any other CFD tools

Advanced Engine Models

CONVERGE™ is the ideal platform for internal combustion engine simulations. CONVERGE™

contains state of the art sub-models including:

Spray models

Combustion models

Turbulence models

Emissions models


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In addition, there is no user grid generation time associated with CONVERGE™ simulations.

The user can go from the CAD surface file to running the simulation in 1-3 hours for complex

geometries with moving boundaries.

CONVERGE™ Modeling

CONVERGE™ is a general purpose 3D CFD Code with focus on engine simulation.

CONVERGE™ is very efficient and accurate, where complex geometries and/or moving

geometries and Chemistry are to be modeled.

The goal of writing CONVERGE was to make engine modeling fast, easy and accurate. To

this end, CONVERGE generates a mesh automatically at runtime thus eliminating all user

meshing time.

There are many and flexible ways to adjust the simulation grid resolution in space and in

time.

There are many accuracy benefits of CONVERGE as well, including using a stationary and

orthogonal mesh in the interior of your domain, whose grid density automatically varies to

resolve gradients using adaptive mesh refinement (AMR).CONVERGE is loaded with the physical models needed to accurately simulate HCCI, Diesel

and spark ignited engines. Included are advanced spray and combustion models, including

the SAGE detailed chemistry solver. Of course, CONVERGE runs well in parallel as well.

CONVERGE™ Features

No User Grid Generation

Engine Models

Structured, Cartesian Mesh

True Geometry Representation Moving Boundaries

Grid Size Scaling

Fixed Grid Embedding

Adaptive Mesh Refinement

Full Parallelization

Discrete Phase Sub-Models

Advanced Combustion Models

LES/RANS Turbulence Models

Conjugate Heat Transfer Models

Design Optimization using Genetic Algorithm

Applications

Multiple Cylinder Simulations

Since there is no user time spent meshing with CONVERGE™, modeling multiple cylinders is

practically as easy as simulating a single cylinder. This can remove the need to determine

port boundary conditions using cycle simulation packages, as the user can include as much

of the intake and/or exhaust manifolds as they wish with as much or as little mesh


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resolution as is desired in each region. This allows for a range of engine simulations that

were not previously practical, including:

Simulation of cylinder-to-cylinder effects. By adequately resolving all of the cylinders,

cylinder-to-cylinder variations can be studied.

Simulation of transient pressure conditions with emphasis on one cylinder. With this

approach, adequate resolution would be used for one of the cylinders to obtain

accurate combustion predictions. The other cylinders could be modeled in a coarse

manner with the goal of capturing the correct cylinder pressure at exhaust valve

opening. In essence, these “coarse cylinders” are included only to help determine

boundary conditions for the “resolved cylinder.”

The image below shows simulated contours of velocity magnitude (at a crank angle during

the intake stroke of cylinder #1) for a four cylinder spark ignited engine. Courtesy Chrysler

Group LLC.

CI Engines

CONVERGE™ is ideally suited for simulating Diesel engines and is used by engine

manufacturers such as Caterpillar Inc. Features such as easy inclusion of complex and

moving geometries, adaptive mesh refinement, and a suite of state-of-the-art spray and

combustion models makes CONVERGE™ the ideal CFD code for all of your IC Engine

applications.

With CONVERGE™, full engine simulations can be performed without the need for mapping

between different codes.

The image below shows the velocity field during the intake stroke for a small bore, high

speed direct injection Diesel engine.


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Spark Ignited Gasoline Engines

CONVERGE™ is ideally suited for gasoline engine simulations, including Port Fuel Injection

(PFI) and Gasoline Direct Injection (GDI) designs. Features such as easy inclusion of complex

geometries, the SAGE detailed chemistry solver and adaptive mesh refinement allow for fast

simulation setup and accurate results.

For simulating a GDI engine operating in homogeneous mode in CONVERGE™, starting from

the CAD geometry definition, the case was up and running in only 2-3 hours. This setup time

was spent flagging the surfaces for boundary conditions and setting up the input files

(injection specification, valve-lift profiles, etc.). Since the grid is created at runtime in

CONVERGE™, no time was spent creating the computational mesh.

Fuel is injected during the intake stroke, as shown in the image below. In this case a

pressure-swirl atomizer is modeled using CONVERGE’s suite of spray models.

After the fuel has vaporized and mixed with the air, the near-stoichiometric mixture is

ignited. Detailed chemistry is used to model the combustion event, and adaptive mesh

refinement is included to accurately model the flame propagation. The image below shows

a cut-plane colored by temperature. Grid lines are included to illustrate the use of AMR to

track the flame front.


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The image below shows a cut-plane through the spark plug colored by temperature. Grid

lines are included to illustrate the use of AMR to track the flame front.

The image below shows a cut-plane below the valves colored by velocity. Grid lines are

included to illustrate the use of AMR to resolve the flow structures.

Other Flow Applications

External Flow

With CONVERGE, moving body problems are as simple as non-moving ones. Thus you

can either calculate the Drag / forces using the steady solver, or simulate for example

the effect of a moving rearwing on a racecar.

For example, calculating the transient loads associated with the tailgate opening is very

simple:

• The tailgate would need to be flagged as a unique (detached) boundary in the

preprocessor

• Then, in the boundary condition file, the tailgate boundary would need to be specified

as a moving boundary with a motion specified by the user (perhaps constant angular

velocity)


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• The transient solver would need to be enabled

• The case would be solved as normal, and every timestep, the solver would rotate the

tailgate appropriately and generate a new volume mesh automatically

Embedding, grid scaling and AMR all are relative to the base grid size. With these

enabled, the user is encouraged to perform a grid refinement study (varying only the

base mesh) to find the optimum accuracy/speed setting for the base mesh size.

Airfoil

The Mach 10 airfoil simulation below illustrates the use of CONVERGE™ for external flow

calculations. The simulation was performed by using a coarse grid initially and then

turning on embedded refinement. The activation of refinement was done automatically

while the simulation was running (i.e., the simulation does not need to be stopped andrestarted with a new grid).

Three types of embedding are used in this simulation:

Grid Size Scaling - All cells are reduced in size by one scale (i.e., a factor of two).

Fixed Grid Embedding - Four layers of cells are placed on the boundary at an embed

scale of six.

Adaptive Mesh Refinement - AMR

is activated on the velocity field

with an embed scale of five for the

smallest allowed cells and the total

number of cells is capped at

250,000.


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Turbine Simulations

Conjugate Heat Transfer

Nozzle Simulations

Relevant Images and link for Video Files

Winklhofer Nozzle

Velocity Contour at p=90bar


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3D Nozzle Sector

Void Fraction and Streamlines at p=90bar

Mass Flow Comparison with Experimental Measurements


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www.convergecfd.com www.ceisoftware.in

3D Nozzle Cavitation (Void Fraction Contour)

3D Nozzle Cavitation (Velocity Contour)

3D Nozzle Cavitation (Void fraction Contour)
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