CONVERGE Features, Capabilities and Applications

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1 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 onthe-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 near nozzles 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 and emissions 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.

2 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

3 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

4 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.

5 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.

6 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)

7 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 and restarted 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.

8 Turbine Simulations Conjugate Heat Transfer Nozzle Simulations Relevant Images and link for Video Files Winklhofer Nozzle Velocity Contour at p=90bar

9 Void Fraction and Streamlines at p=90bar Mass Flow Comparison with Experimental Measurements 3D Nozzle Sector

10 3D Nozzle Cavitation (Void Fraction Contour) 3D Nozzle Cavitation (Void fraction Contour) 3D Nozzle Cavitation (Velocity Contour)