Glossary of Terms

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Glossary of Terms for Fluent Computational Fluid Dynamics (CFD)

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

CAD: Acronym for Computer-Aided Design
Software solutions for authoring product design.
CAD-Embedding: A term to describe CAE software with close coupling associated with a direct embedding within Computer-Aided Design software. This includes a native GUI within the CAD system.
CAE: Acronym for Computer-Aided Engineering
Software solutions for simulating the physical behavior of a future product.
CAM: Acronym for Computer-Aided Manufacturing
Software solutions for defining manufacturing operations.
CFD: Acronym for Computational Fluid Dynamics
CFD is a computer-based mathematical modeling tool that incorporates the solution of the fundamental equations of fluid flow, the Navier-Stokes equations, and other allied equations. CFD incorporates empirical models for modeling turbulence based on experimentation, as well as the solution of heat, mass and other transport and field equations. There are three phases to CFD: preprocessing, or creation of a geometry usually done in a CAD tool; mesh generation of a suitable computational domain to solve the flow equations on; and solving with postprocessing, or visualization of a CFD code’s predictions. CFD is now a widely accepted and validated engineering tool for industrial applications. The FLUENT CFD code is the most widely used and popular CFD software in the world.
Collaborative Workspace: An inter-connected environment in which all the participants in the product lifecycle (design, marketing, sales, manufacturing, OEMs, suppliers, and customers) can access and interact with each other's "In-Work" designs, thereby enhancing communication through rapid exchange, direct use, simulation and validation in 3D.
CRM: Acronym for Customer Relationship Management
A business strategy that helps companies manage customer relationships. For example, a CRM database enables a company to access individual customer information, match customer needs with product plans and offerings, stay abreast of customer service requirements, and be aware of previous customer purchases. CRM involves managing customer relationships on a more informed basis and tailoring them to better meet the customers' needs.
DEM: Acronym for Discrete Element Modeling
This is a numerical technique which solves engineering problems that are modeled as a large system of distinct interacting general shaped (deformable or rigid) bodies or particles that are subject to gross motion. Engineering problems that exhibit such large scale discontinuous behavior cannot be solved with a conventional continuum based procedure such as the Finite Element Method.
DES: Acronym for Detached Eddy Simulation
The DES capability is a turbulence model based on the one-equation eddy-viscosity transport model of Spalart and Allmaras. In the near-wall region, the DES model reduces to the original RANS model of Spalart and Allmaras, while it acts as a subgrid-scale turbulence model away from the wall.
DNS: Acronym for Direct Numerical Simulation
This is a CFD method by which the complete turbulent flow field is solved directly numerically without any form of time or length averaging in the domain, i.e. both the mean flow and all turbulent eddies (fluctuations) are simulated. DNS is very computationally intensive and currently only practicable for simple flows at low Reynolds Numbers.
DPM: Acronym for Discrete Phase Model
In addition to solving transport equations for the continuous fluid phase in a CFD simulation, FLUENT allows you to simulate a discrete second phase in a Lagrangian frame of reference. This second phase can consist of spherical particles (which may be taken to represent droplets or bubbles) dispersed in the continuous phase. Trajectories of these discrete phase entities, as well as heat and mass transfer to/from them can be modeled.
EACC: Acronym for European Automotive CFD Conference
This event is hosted by Fluent biennially in Europe. It is the largest Automotive CFD event in the world and a forum for innovative leading edge CFD, CAE and PLM in the automotive industry worldwide. For more information, visit www.eacc.fluent.com
FEM: Acronym for Finite Element Method
This is a numerical technique for solving boundary-value problems. In a fluid flow application, the flow domain can be represented by finite elements, i.e. a geometrically similar model consists of several simplified discrete regions, which are linked. Flow governing equations (mass and momentum conservation, constitutive equations) are applied to each element, and a system of equations is constructed in terms of nodal unknowns. Techniques of linear algebra, combined with non-linear numerical schemes are subsequently invoked for solving the system.
FVM: Acronym for Finite Volume Method
This is a method for representing and evaluating partial differential equations (PDE) as algebraic equations.
FSI: Acronym for Fluid-Structure Interaction
This is a model that allows for the deformation of solid boundaries to be taken into account when there is physical interaction with a flow field. This is relevant in applications where deformations undergone by boundaries are significant and affect the flow domain. FSI encompasses those physical phenomena for which aerodynamic (hydrodynamic), elastic (structural), and inertial (dynamic) forces influence each other and interact in a significant way. Aeroelasticity (Hydroelasticity) is an important subset of fluid-structure interaction. Flutter in aircraft is a subset of aeroelasticity. Vortex-Induced Vibration (VIV) is a subset of hydroelasticity. Modeling FSI can usually be achieved by coupling a CFD code with a structural analysis code.
GUI: Acronym for Graphical User Interface
This is a computer screen interface that presents information (often applications, i.e. CFD codes) in a user-friendly way using pictures, graphics and icons.
IGES: Acronym for Initial Graphics Exchange Specification
This is an agreed international neutral file format used to translate geometrical information between different CAD, CAE and analysis software packages. Visit www.nist.gov/iges/ for details.
LES: Acronym for Large Eddy Simulation
This is a compromise between DNS and RANS. In DES, the unsteady flow equations are solved for the mean flow and large eddies of a flow field and a “sub grid scale” model is used to simulate the effects of the smaller eddies. Since it is the largest eddies which contain the most energy and interact most with the mean flow, the LES approach results in a good model of the main effects of turbulence. Since the grid size no longer has to be small enough to allow for the smallest turbulent eddies, this method is much less computationally expensive as DNS and may be applied to a wider range of flows. However, time dependent meshes using relatively fine meshes are still necessary, so the computational requirement is still high. LES is valuable for predicting aeroacoustic flows.
Mechanical Design: The conception, modelization, and design of mechanical systems. From concept to detailed design, and on to drawing production, mechanical design products accelerate core activities of product development. Mechanical design products also address sheet metal and mold manufacturer requirements through dedicated applications that dramatically enhance productivity and strongly reduce time-to-market.
MRF: Acronym for Multiple Reference Frame
This is a steady state CFD method that simplifies the flow effects of a transient moving body with a fixed shape in a computer simulation. It is very commonly used for modeling impellers in mixing tanks and rotor/stator turbomachinery interactions for instance.
MST: Acronym for Mesh Superposition Technique
A technique based on overlapping meshes. As an example, it is used in the POLYFLOW software for the simulation of fluid flows surrounding fixed or moving solid bodies with complex geometric shapes.
PDF: Acronym for Probability Density Function
This is the description of the probability of an event at a given value of an independent variable and is especially used in chemical reaction modeling.
PLM: Acronym for Product Lifecycle Management
A business strategy that helps companies share product data, apply common processes, and leverage corporate knowledge for the development of products from conception to retirement across the extended enterprise. By including all actors (company departments, business partners, suppliers, OEM, and customers), PLM enables this entire network to operate as a single entity to conceptualize, design, build, and support products. Defined broadly, PLM is an information-driven approach to all aspects of a product’s life, from design to manufacture to deployment and maintenance, eventually ending when the product is removed from service and disposed. Imagine all of these steps enabled by a set of highly integrated processes, methods, and tools. PLM systems are really an outgrowth of product document management, or PDM systems, and are geared more toward CAD data than simulation data.
RANS: Acronym for Reynolds Averaged Navier-Stokes
This is a form of the Navier-Stokes equations for describing fluid flow in which additional terms (known as Reynolds Stresses) are included in the solver to account for the time-averaged effects of turbulence. It is the standard method used in the FLUENT CFD code.
Rapid Flow Modeling: There is constant pressure in the engineering design community to reduce development time, while continuing to produce competitive and innovative products. Techniques to reduce time-to-market for new products are usually called “rapid”, e.g.: rapid design, rapid prototyping, rapid tooling, and rapid manufacturing. Rapid flow modeling is an approach to CFD simulation that allows for accurate and quick engineering design validation early in the product development cycle. Fluent’s CFD design software, FloWizard, is a rapid flow modeling tool.
RLicense: As part of Fluent’s continuing eBusiness initiative, Fluent has developed a usage-based licensing service. Fluent’s RLicense Service provides authorized users with the ability to generate additional license keys (RLicenses) for overdraft or mobile usage. Each RLicense can be customized to best match project needs based on product mix, process count, and duration.
RNG k-epsilon Turbulence Model: Acronym for ReNormalization Group
This is a variant of the standard k-epsilon turbulence model where the model constants are derived by Renormalization Group theory and are based on statistical techniques as opposed to the empirical techniques used in the standard k-epsilon model.
RSF or RSolve: Acronym for Remote Simulation Facility
Using the Fluent RSolve Service and the Remote Simulation Facility (RSF), trained users can take advantage of "supercomputer" capacity for the execution of large or complex simulations. The RSF portal provides for fully secure 128 bit encrypted SSL service that is monitored and available 24 hours a day, 7 days a week, 365 days a year. FLUENT 6 is now available for use on RSolve via a secure portal from the Internet.
RSM: Acronym for Reynolds Stress Model
This is a more accurate (and computationally intensive) second-moment closure turbulence model, which employs 6 equations for Reynolds Stress Transport along with the scalar turbulent dissipation rate rather than the 2 equation k-epsilon type turbulence model.
SPDM: Acronym for Simulation Process and Data Management
This integrates the processes and data involved in engineering design. SPDM aims to simplify the use of powerful CAE technologies so that they are available to a wider group of companies for evaluating more designs more thoroughly at a much earlier stage in the design process as well as capture the knowledge and codify the process of CAE usage. Such an approach can deliver substantial improvements in product design and performance while reducing product development lead time and costs. Fluent’s sister company, Enductive Inc., is an expert service provider in this field.
STEP: Acronym for Standard for the Exchange of Product Model Data
This is an international standard for the exchange of digital product information (ISO 10303). Visit www.steptools.com/library/standard/ for details.
UDF: Acronym for User-Defined Function
This is a subroutine of code that can be written by the user and linked into Fluent’s general purpose CFD code solvers to perform certain custom operations such as initialization, special boundary conditions, new materials properties, source terms, reaction rates and postprocessing, and reporting enhancements.
UGM: Acronym for User Group Meeting
These are regular (usually annual) events held locally on a geographical basis worldwide, where Fluent’s customers, partners and other interested parties hear of developments in Fluent’s products and services, as well as meet with other CFD users and hear user CFD application stories.
USC: Acronym for User Service Center
This is Fluent’s unique passworded customer service web site. It includes a wealth of up-to-date information on Fluent’s products including beta releases, frequently asked questions, online technical support, training information, manuals, discussion forums, software downloads, CFD literature and other CFD resources.
VOF: Acronym for Volume of Fluid/Flow Model
The VOF model is used mainly for multiphase flows, and in particular free surface (or wave) flows. Motion of fluid interfaces based on the solution of a conservative transport equation for the fractional volume of fluid in a grid cell is the method employed in FLUENT.
VPD: Acronym for Virtual Product Development
Nearly every enterprise realizes that it needs to bring higher-quality products to market faster to get an advantage over the competition; the goal being increased market share and higher profit margins. One way to achieve this goal is to replace the tried and true “build and test” approach to product design with the Virtual Product Development (VPD) paradigm, which brings powerful computer-aided engineering (CAE) simulation tools to bear on the design process to dramatically reduce the build and test cycle time. Because these tools become increasingly important to design and manufacturing, and as CAE becomes more critical to the design process, limitations in their use are becoming apparent. Fluent’s sister company, Enductive Inc., is an expert service provider in this field.
Virtual Prototyping: The virtual design and simulation in 3D of a product and all of its components. Digital or virtual mock-up eliminates the need for expensive real mock-up. Manufacturers can design a mock-up of a product in full detail, simulating all functions and anticipating interaction among the different components. Since digital mock-up contains all of the data associated with the product, it is richer than physical mock-up because all simulation and calculations can be performed on it.

Glossary of Terms
Company Profile History of Fluent Fluent's Technology Advantage ISO/TickIT Registration Jobs/Careers Learn about CFD What is CFD A Brief History of CFD Glossary of Terms	Glossary of Terms for Fluent Computational Fluid Dynamics (CFD) A B C D E F G H I J K L M N O P Q R S T U V W X Y Z CAD Acronym for Computer-Aided Design Software solutions for authoring product design. CAD-Embedding A term to describe CAE software with close coupling associated with a direct embedding within Computer-Aided Design software. This includes a native GUI within the CAD system. CAE Acronym for Computer-Aided Engineering Software solutions for simulating the physical behavior of a future product. CAM Acronym for Computer-Aided Manufacturing Software solutions for defining manufacturing operations. CFD Acronym for Computational Fluid Dynamics CFD is a computer-based mathematical modeling tool that incorporates the solution of the fundamental equations of fluid flow, the Navier-Stokes equations, and other allied equations. CFD incorporates empirical models for modeling turbulence based on experimentation, as well as the solution of heat, mass and other transport and field equations. There are three phases to CFD: preprocessing, or creation of a geometry usually done in a CAD tool; mesh generation of a suitable computational domain to solve the flow equations on; and solving with postprocessing, or visualization of a CFD code’s predictions. CFD is now a widely accepted and validated engineering tool for industrial applications. The FLUENT CFD code is the most widely used and popular CFD software in the world. Collaborative Workspace An inter-connected environment in which all the participants in the product lifecycle (design, marketing, sales, manufacturing, OEMs, suppliers, and customers) can access and interact with each other's "In-Work" designs, thereby enhancing communication through rapid exchange, direct use, simulation and validation in 3D. CRM Acronym for Customer Relationship Management A business strategy that helps companies manage customer relationships. For example, a CRM database enables a company to access individual customer information, match customer needs with product plans and offerings, stay abreast of customer service requirements, and be aware of previous customer purchases. CRM involves managing customer relationships on a more informed basis and tailoring them to better meet the customers' needs. DEM Acronym for Discrete Element Modeling This is a numerical technique which solves engineering problems that are modeled as a large system of distinct interacting general shaped (deformable or rigid) bodies or particles that are subject to gross motion. Engineering problems that exhibit such large scale discontinuous behavior cannot be solved with a conventional continuum based procedure such as the Finite Element Method. DES Acronym for Detached Eddy Simulation The DES capability is a turbulence model based on the one-equation eddy-viscosity transport model of Spalart and Allmaras. In the near-wall region, the DES model reduces to the original RANS model of Spalart and Allmaras, while it acts as a subgrid-scale turbulence model away from the wall. DNS Acronym for Direct Numerical Simulation This is a CFD method by which the complete turbulent flow field is solved directly numerically without any form of time or length averaging in the domain, i.e. both the mean flow and all turbulent eddies (fluctuations) are simulated. DNS is very computationally intensive and currently only practicable for simple flows at low Reynolds Numbers. DPM Acronym for Discrete Phase Model In addition to solving transport equations for the continuous fluid phase in a CFD simulation, FLUENT allows you to simulate a discrete second phase in a Lagrangian frame of reference. This second phase can consist of spherical particles (which may be taken to represent droplets or bubbles) dispersed in the continuous phase. Trajectories of these discrete phase entities, as well as heat and mass transfer to/from them can be modeled. EACC Acronym for European Automotive CFD Conference This event is hosted by Fluent biennially in Europe. It is the largest Automotive CFD event in the world and a forum for innovative leading edge CFD, CAE and PLM in the automotive industry worldwide. For more information, visit www.eacc.fluent.com FEM Acronym for Finite Element Method This is a numerical technique for solving boundary-value problems. In a fluid flow application, the flow domain can be represented by finite elements, i.e. a geometrically similar model consists of several simplified discrete regions, which are linked. Flow governing equations (mass and momentum conservation, constitutive equations) are applied to each element, and a system of equations is constructed in terms of nodal unknowns. Techniques of linear algebra, combined with non-linear numerical schemes are subsequently invoked for solving the system. FVM Acronym for Finite Volume Method This is a method for representing and evaluating partial differential equations (PDE) as algebraic equations. FSI Acronym for Fluid-Structure Interaction This is a model that allows for the deformation of solid boundaries to be taken into account when there is physical interaction with a flow field. This is relevant in applications where deformations undergone by boundaries are significant and affect the flow domain. FSI encompasses those physical phenomena for which aerodynamic (hydrodynamic), elastic (structural), and inertial (dynamic) forces influence each other and interact in a significant way. Aeroelasticity (Hydroelasticity) is an important subset of fluid-structure interaction. Flutter in aircraft is a subset of aeroelasticity. Vortex-Induced Vibration (VIV) is a subset of hydroelasticity. Modeling FSI can usually be achieved by coupling a CFD code with a structural analysis code. GUI Acronym for Graphical User Interface This is a computer screen interface that presents information (often applications, i.e. CFD codes) in a user-friendly way using pictures, graphics and icons. IGES Acronym for Initial Graphics Exchange Specification This is an agreed international neutral file format used to translate geometrical information between different CAD, CAE and analysis software packages. Visit www.nist.gov/iges/ for details. LES Acronym for Large Eddy Simulation This is a compromise between DNS and RANS. In DES, the unsteady flow equations are solved for the mean flow and large eddies of a flow field and a “sub grid scale” model is used to simulate the effects of the smaller eddies. Since it is the largest eddies which contain the most energy and interact most with the mean flow, the LES approach results in a good model of the main effects of turbulence. Since the grid size no longer has to be small enough to allow for the smallest turbulent eddies, this method is much less computationally expensive as DNS and may be applied to a wider range of flows. However, time dependent meshes using relatively fine meshes are still necessary, so the computational requirement is still high. LES is valuable for predicting aeroacoustic flows. Mechanical Design The conception, modelization, and design of mechanical systems. From concept to detailed design, and on to drawing production, mechanical design products accelerate core activities of product development. Mechanical design products also address sheet metal and mold manufacturer requirements through dedicated applications that dramatically enhance productivity and strongly reduce time-to-market. MRF Acronym for Multiple Reference Frame This is a steady state CFD method that simplifies the flow effects of a transient moving body with a fixed shape in a computer simulation. It is very commonly used for modeling impellers in mixing tanks and rotor/stator turbomachinery interactions for instance. MST Acronym for Mesh Superposition Technique A technique based on overlapping meshes. As an example, it is used in the POLYFLOW software for the simulation of fluid flows surrounding fixed or moving solid bodies with complex geometric shapes. PDF Acronym for Probability Density Function This is the description of the probability of an event at a given value of an independent variable and is especially used in chemical reaction modeling. PLM Acronym for Product Lifecycle Management A business strategy that helps companies share product data, apply common processes, and leverage corporate knowledge for the development of products from conception to retirement across the extended enterprise. By including all actors (company departments, business partners, suppliers, OEM, and customers), PLM enables this entire network to operate as a single entity to conceptualize, design, build, and support products. Defined broadly, PLM is an information-driven approach to all aspects of a product’s life, from design to manufacture to deployment and maintenance, eventually ending when the product is removed from service and disposed. Imagine all of these steps enabled by a set of highly integrated processes, methods, and tools. PLM systems are really an outgrowth of product document management, or PDM systems, and are geared more toward CAD data than simulation data. RANS Acronym for Reynolds Averaged Navier-Stokes This is a form of the Navier-Stokes equations for describing fluid flow in which additional terms (known as Reynolds Stresses) are included in the solver to account for the time-averaged effects of turbulence. It is the standard method used in the FLUENT CFD code. Rapid Flow Modeling There is constant pressure in the engineering design community to reduce development time, while continuing to produce competitive and innovative products. Techniques to reduce time-to-market for new products are usually called “rapid”, e.g.: rapid design, rapid prototyping, rapid tooling, and rapid manufacturing. Rapid flow modeling is an approach to CFD simulation that allows for accurate and quick engineering design validation early in the product development cycle. Fluent’s CFD design software, FloWizard, is a rapid flow modeling tool. RLicense As part of Fluent’s continuing eBusiness initiative, Fluent has developed a usage-based licensing service. Fluent’s RLicense Service provides authorized users with the ability to generate additional license keys (RLicenses) for overdraft or mobile usage. Each RLicense can be customized to best match project needs based on product mix, process count, and duration. RNG k-epsilon Turbulence Model Acronym for ReNormalization Group This is a variant of the standard k-epsilon turbulence model where the model constants are derived by Renormalization Group theory and are based on statistical techniques as opposed to the empirical techniques used in the standard k-epsilon model. RSF or RSolve Acronym for Remote Simulation Facility Using the Fluent RSolve Service and the Remote Simulation Facility (RSF), trained users can take advantage of "supercomputer" capacity for the execution of large or complex simulations. The RSF portal provides for fully secure 128 bit encrypted SSL service that is monitored and available 24 hours a day, 7 days a week, 365 days a year. FLUENT 6 is now available for use on RSolve via a secure portal from the Internet. RSM Acronym for Reynolds Stress Model This is a more accurate (and computationally intensive) second-moment closure turbulence model, which employs 6 equations for Reynolds Stress Transport along with the scalar turbulent dissipation rate rather than the 2 equation k-epsilon type turbulence model. SPDM Acronym for Simulation Process and Data Management This integrates the processes and data involved in engineering design. SPDM aims to simplify the use of powerful CAE technologies so that they are available to a wider group of companies for evaluating more designs more thoroughly at a much earlier stage in the design process as well as capture the knowledge and codify the process of CAE usage. Such an approach can deliver substantial improvements in product design and performance while reducing product development lead time and costs. Fluent’s sister company, Enductive Inc., is an expert service provider in this field. STEP Acronym for Standard for the Exchange of Product Model Data This is an international standard for the exchange of digital product information (ISO 10303). Visit www.steptools.com/library/standard/ for details. UDF Acronym for User-Defined Function This is a subroutine of code that can be written by the user and linked into Fluent’s general purpose CFD code solvers to perform certain custom operations such as initialization, special boundary conditions, new materials properties, source terms, reaction rates and postprocessing, and reporting enhancements. UGM Acronym for User Group Meeting These are regular (usually annual) events held locally on a geographical basis worldwide, where Fluent’s customers, partners and other interested parties hear of developments in Fluent’s products and services, as well as meet with other CFD users and hear user CFD application stories. USC Acronym for User Service Center This is Fluent’s unique passworded customer service web site. It includes a wealth of up-to-date information on Fluent’s products including beta releases, frequently asked questions, online technical support, training information, manuals, discussion forums, software downloads, CFD literature and other CFD resources. VOF Acronym for Volume of Fluid/Flow Model The VOF model is used mainly for multiphase flows, and in particular free surface (or wave) flows. Motion of fluid interfaces based on the solution of a conservative transport equation for the fractional volume of fluid in a grid cell is the method employed in FLUENT. VPD Acronym for Virtual Product Development Nearly every enterprise realizes that it needs to bring higher-quality products to market faster to get an advantage over the competition; the goal being increased market share and higher profit margins. One way to achieve this goal is to replace the tried and true “build and test” approach to product design with the Virtual Product Development (VPD) paradigm, which brings powerful computer-aided engineering (CAE) simulation tools to bear on the design process to dramatically reduce the build and test cycle time. Because these tools become increasingly important to design and manufacturing, and as CAE becomes more critical to the design process, limitations in their use are becoming apparent. Fluent’s sister company, Enductive Inc., is an expert service provider in this field. Virtual Prototyping The virtual design and simulation in 3D of a product and all of its components. Digital or virtual mock-up eliminates the need for expensive real mock-up. Manufacturers can design a mock-up of a product in full detail, simulating all functions and anticipating interaction among the different components. Since digital mock-up contains all of the data associated with the product, it is richer than physical mock-up because all simulation and calculations can be performed on it.