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ACRi -- Analytic & Computational Research, Inc.





The new, better-than-ever version 6.0 of ANSWER, the general purpose CFD Software developed by ACRi is released. On top of the many stability and versatility features built into the solver, ANSWER now comes bundled with CFDStudio, the integrated development environment for CFD applications.

Among the many other new features are:

  • Gridless Computing (2D only, 3D under development). (*)
  • Support extended to Hybrid elements such as prisms, pyramids, tetrahedra as well as hexahedra (3D); triangles as well as quads (2D). Any combination of elements are acceptable. (*)
  • Adaptive Gridding / Auto Refinement at runtime based on certain runtime criteria. (*)
  • If-then-else type of conditional statements.
  • Better matrix solution control.
  • Computational improvements for better interpolation of values at faces.
  • Many other improvements... See New Features Sheet for a detailed list.

(*) These features may have an additional cost, depending on your licensing agreement.

Click on this link or the link on left hand side to request an evaluation copy of ANSWER.

General Features:

ANSWER is highly modular and presents a versatile interface to the user. It provides a platform to quickly experiment with new physical models, numerical schemes, matrix solvers, etc. Among its distinctive features are:

  • The exclusive usage of CFDStudio, the new integrated development environment for ANSWER which significantly shortens the learning curve
  • A powerful yet simple English-like, self-documenting FREEFORM™ interface which allows user to define a complex problem with a few simple commands.
  • User can define new field variables with arbitrary names on the fly without writing a single line of code.
  • User can solve arbitrary number of new transport equations with user-defined properties, sources, and boundary conditions without a single line of code.
  • User can implement arbitrary multi-step kinetics without writing code.
  • User can implement arbitrary and complex functions for sources, boundary conditions, field variables and fluid and matrix properties with simple English-like commands.
  • ANSWER provides a wide variety of physical sub-models for turbulence and combustion.
  • ANSWER provides alternative numerical methods and matrix solvers.
  • ANSWER is highly modular and can easily integrate external solvers, numerical methods and problem specific algorithms.

Physics and Computational Features for the Detail-Oriented:

A wide variety of physical models are already implemented in ANSWER.

  • Transient or Steady state
  • Compressible or Incompressible fluid

Turbulence Models:

  • Near wall models:
    • Launder-Sharma
    • Chien
    • So-Sarkar
    • Yeang-Shih
  • Standard k-ε
  • k-ε with RNG
  • Non-linear Quadratic k-ε (Lumley-Shih)
  • Non-linear Cubic k-ε (Lumley-Shih)
  • Differential RSM(Craft-Ince-Launder)
  • LES (Implemented by UCLA/Northrop)
  • Wilcox's k-ω
  • Mentor's blended k-ε-ω

Combustion models:

  • 1,2,3 and 4-Step Hydrocarbon Model
  • 3 or 5-Step Univ. of Washington Hydrocarbon Model
  • User-defined multi-step multi-species reaction systems with/without turbulence limiting
  • Arbitrary 1st, 2nd or 3rd order Arrhenius Kinetics with or without EBU/turbulent limiting
  • Fast-Chemistry assumed PDF
  • Flamelet (Implemented by Prof. Candel for SMECMA)
  • Mass Transport with Unlimited number of Species


  • Direct, Mass Injection, Solubility Limited, Radiation or Arrhenius Kinetics
  • Sources that are functions of surface area or volume
  • Functions of time, space or any dependent or user-defined variable
  • Any number and mix of sources for any variable
  • Boundary Conditions: Dirichlet, Neuman, Radiation and other derived types

Heat Transfer:

  • Conjugate heat transfer with embedded solids
  • Sub-models for Spray, Radiation, Regeneration and other physical phenomena
  • Built-in six-flux radiation model
  • Interface with heat ordinate radiation model


  • Structured or Unstructured Meshes
  • Arbitrary quadrilateral or Hexahedral control volumes
  • Specialized 2D and/or Cylindrical modes
  • Specialized 2D Cylindrical mode with a third swirl velocity component
  • Built-in geometry and meshing for geometrically and topologically simple problems

A brief History...

During the past 25 years, ANSWER has evolved from a simple mathematical model for flow and heat transfer into a comprehensive Computational Fluid Dynamics software tool for analysis of a wide range of problems. It provides for coupled transport of fluid, heat and multiple chemical species in complex three-dimensional geometry. It is able to simulate the transient or steady state behavior of laminar or turbulent flow in compressible or incompressible fluids with chemical reactions, combustion, liquid sprays, droplet burning, soot formation, and radiation. It has grown from a simple computer code with few modules and fewer options to a software package with almost 1000 modules and a versatile set of options that can accommodate almost any user requirements.

ANSWER has been used to analyze problems as diverse as low pressure film deposition, cooling of electronic components, automobile fluid dynamics, ventilation of tunnels, HVAC design optimization, analysis of process tanks, design of ramjets and aircraft engines, and missile launch tube simulations, lubrication of bearings, and performance of high Mach number missiles.

In the process, ANSWER has evolved with the user's needs. At every stage, the flexibility and generality of the software were maintained while options were added to address user requirements. As a result, today ANSWER provides a flexible format that is bound neither to a specific algorithm, nor to a particular methodology. Rather, it provides a framework that facilitates experimentation. The user can change numerical schemes, solution method, matrix inversion algorithms, or any of the physical or mathematical features.

Of all features of ANSWER, two deserve special mention: generality of applications over a diverse range of problems, and ease of use provided by the conversational FREEFORM command language. These have enabled ANSWER to emerge as a leading software in its field of application.

ANSWER™ is distinguished by the diversity of its users. It is being used by commercial, research and educational organizations in 6 countries. Among its users are Aerospatiale (France), Allison Gas Turbine, ASCI, S.A. (Spain), BAe-Sema (U.K.), C.N.I.M. (France), Department of Education (Mexico), GERPY (FRANCE), General Electric Company, James M. Montgomery, Lam Research Corporation, Marquardt Company, National Aeronautical and Space Administration, Renault (France), SNECMA (France), University of California, US Air Force, Watkins-Johnson, WS Atkins (UK), and a number of other commercial organizations. Over 100 publications and project reports on the benchmarking, verification and application of ANSWER™ are currently available.

Related Links:

ANSWER Applications
ANSWER Examples
ANSWER Express
ANSWER Publications
ANSWER Price List
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