CFX Expression Language – Part 1: Accessing CFD Simulation Information in CFX (and FLUENT)

Categories:

This week we are presenting an introduction to CFX Expression Language. If you’re not familiar with CFX, it is one of the two CFD tools available from ANSYS, Inc., the other being Fluent. CFX has been part of the ANSYS family of engineering tools since 2003. It is relatively easy to use and can be run stand-alone or tightly integrated with other ANSYS products within ANSYS Workbench. We have some general information on CFX available at this link.

CFX Expression Language, or CEL, is the scripting language that allows us to define inputs as variables, capture outputs as variables, and perform operations on those variables. Through the use of CEL we can be more efficient in our CFD runs and better capture results that we need. With CEL we can access and manipulate information without needing to recompile code or access separate routines besides the main CFX applications.

Also note that since CEL can be used in CFD Post, it is useful for postprocessing FLUENT solutions in addition to CFX, since CFD Post is common to both CFX and FLUENT. There are some things to be aware of regarding FLUENT In CFD Post. This link in to the ANSYS 14.5 Help system explains it:

// User’s Guide :: 0 // 7. CFD-Post File Menu // 7.15. File Types Used and Produced by CFD-Post // 7.15.10. Limitations with FLUENT Files

If you are a user of APDL, ANSYS Parametric Design Language, what I have written above about CEL should look familiar. One difference, though, is that while Mechanical APDL is dimensionless, CFX is not. Therefore, CEL definitions contain units where appropriate.

CEL is typically used in CFX-Pre and CFD-Post. A handy editor is available to assist in the definition of the expressions. Most of the activity is enabled by right clicking.

Virtually any quantity in CFX that requires a value input can make use of CEL, including boundary conditions and material properties. CEL can also be used to access and enhance results information. Expressions defined in CEL can be used in design point studies in ANSYS Workbench, either as input or output parameters.

So, what kind of things can you do in an expression? In addition to accessing simulation information and storing it as a variable, you can manipulate values using operators such as add, subtract, multiply, divide, and raise to a power. You can also use built-in functions such as sine, cosine, tangent and other trig functions, exponent, log, square root, absolute value, minimum, maximum, etc.

There are many predefined values, including some common CFD constants such as pi, the universal gas constant, and Avogadro’s number. The available options are different in CFX pre vs. CFD Post, with relevant choices for each.

In CFX Pre, expressions are accessed by double clicking on Expressions in the tree. That takes you to the expression editor, as shown here:

image

Notice how units are defined for each expression, but they can be mixed if desired.

Regarding CFD Post, the example below shows three expressions defined in CFD Post. The expressions within the box are user-defined. The other expressions listed are setup automatically.

The values for forceX1 and forceX2 are calculated by extracting X-direction forces on two different surfaces. The surface names were defined in ANSYS Meshing in this case, as Named Selections. The value fdiffx is calculated by subtracting forceX1 from forceX2. The resulting value, fdiffx, has been specified as an output parameter in Workbench; hence the P-> symbol next to the name.

clip_image004

New expressions are created by right-clicking in the Expressions tab. The new expression value is given a name, then the definition is input, typically by right clicking and selecting from the menus of available quantities, like this:

clip_image006

The location of application for an expression can also be selected by right clicking:

clip_image008

So we’ve got our variables defined using CEL. Now what? Here are some things we can do with CEL variables:

1. Use them as inputs such as material properties or boundary condition values in CFX. If we are running multiple cases, it is typically much easier to define quantities that we want to vary this way. The values can then be changes in the Expression Window, or if defined as a parameter in Workbench, in the parameters view as part of a parameter study.

2. Use them for reporting results quantities of interest, such as forces at a desired location.

3. Use them as input or output parameters in a design point study or design optimization.

Hopefully this brief introduction gives you a glimpse at the power of CEL. In a future article we will look at using CEL for more advanced functionality, such as applying ramped or time varying boundary conditions, using IF statements, and monitoring expression values during solution.

Categories

Certified Elite Channel Partner

Get Your Ansys Products & Support from the Engineers who Contribute to this Blog.

Product Development
Platinum Partner

Technical Expertise to Enable your Addictive Manufacturing Success.

PADT’s Pulse Newsletter

Keep up to date on what is going on at PADT by subscribing to our newsletter.


By submitting this form, you are consenting to receive marketing emails from: Phoenix Analysis and Design Technologies, 7755 S. Research Dr., Tempe, AZ, 85284, https://www.padtinc.com. You can revoke your consent to receive emails at any time by using the SafeUnsubscribe® link, found at the bottom of every email. Emails are serviced by Constant Contact

Share this post:

Upcoming Events

03/29/2023

8th Thermal and Fluids Engineering Conference

03/29/2023

Structural Updates in Ansys 2023 R1 - Composites, Fracture & MAPDL

03/28/2023

8th Thermal and Fluids Engineering Conference

03/27/2023

8th Thermal and Fluids Engineering Conference

03/26/2023

8TH Thermal and Fluids Engineering Conference

03/24/2023

Arizona BioPreneur Conference | Spring 2023

03/22/2023

2023 Arizona MedTech Conference

03/22/2023

Optimize Jigs & Fixtures with Additive - Webinar

03/15/2023

3D Design Updates in Ansys 2023 R1 - Webinar

03/08/2023

Competitive Advantages of 1D/3D Coupled Simulation - Webinar

03/01/2023

High Frequency Updates in Ansys 2023 R1 - Webinar

02/22/2023

Additive Advantages in Aerospace - Webinar

02/15/2023

Structural Updates in Ansys 2023 R1 (1) - Webinar

02/09/2023

IME 2023: MD&M | WestPack | ATX | D&M | Plastek

02/08/2023

IME 2023 MD&M | WestPack | ATX | D&M | Plastek

02/07/2023

IME 2023 MD&M | WestPack | ATX | D&M | Plastek

01/27/2023

Arizona Photonics Days, 2023

01/26/2023

Arizona Photonics Days, 2023

01/26/2023

TIPE 3D Printing | 2023

01/26/2023

Venture Cafe Phoenix Talent Night - Job Fari

01/26/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/25/2023

Arizona Photonics Days, 2023

01/25/2023

Building A.M.- Utah: Kickoff!

01/25/2023

TIPE 3D Printing | 2023

01/25/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/24/2023

VFS 2023 Autonomous/Electric VTOL Symposium

01/24/2023

TIPE 3D Printing | 2023

01/18/2023

2023 AZ Tech Council Golf Tournament

12/21/2022

Simulation Best Practices for 5G Technology - Webinar

12/14/2022

Digital Twins Updates in Ansys 2022 R2 - Webinar

12/08/2022

Tech the Halls - AZ Tech Council Holiday Mixer

12/07/2022

Electric Vehicle and Other Infrastructure Update Panel

11/30/2022

SPEOS Updates in Ansys 2022 R2 - Webinar

11/23/2022

Simulation Best Practices for Electronics Reliability - Webinar

11/16/2022

Discovery Updates in Ansys 2022 R2

11/10/2022

VentureCafe Phoenix Panel: Venture Capital in AZ

11/08/2022

2022 GOVERNOR’S CELEBRATION OF INNOVATION AWARDS + TECH SHOWCASE

11/03/2022

VentureCafe Phoenix Panel: Angel Investment in AZ

11/02/2022

High & Low Frequency Electromagnetics Updates in Ansys 2022 R2

10/26/2022

Simulation Best Practices For Chip-Package-System Design & Development

10/20/2022

Nerdtoberfest 2022

10/19/2022

2022 Southern Arizona Tech + Business Expo

10/19/2022

LS-DYNA Updates in Ansys 2022 R2 - Webinar

10/17/2022

Experience Stratasys Truck Tour - Clearfield Utah

10/14/2022

ASU School of Manufacturing Systems and Networks - Formal Opening Cele

10/14/2022

Experience Stratasys Truck Tour - Midvale Utah

10/12/2022

Experience Stratasys Truck Tour - Littleton Colorado

10/06/2022

Fluids Updates in Ansys 2022 R2 - Webinar

10/05/2022

Experience Stratasys Truck Tour - Colorado Springs

09/29/2022

White Hat Life Science Investor Conference - 2022

09/28/2022

2022 AZBio Awards

09/28/2022

Simulation Best Practices for Rotating Machinery Design & Development

09/21/2022

ExperienceIT NM 2022

09/21/2022

Additive Updates in Ansys 2022 R2 - Webinar

09/14/2022

Rocky Mountain Life Sciences Investor & Partnering Conference

09/08/2022

Ansys Optics Simulation User Group Meeting - Virtual

09/08/2022

Ansys Optics Simulation User Group Meeting

09/07/2022

SI & PI Updates in Ansys 2022 R2 - Webinar

08/31/2022

Simulation Best Practices for Developing Medical Devices - Webinar

08/24/2022

Mechanical Updates in Ansys 2022 R2 - Webinar

08/10/2022

Tucson after5 Tech Mixer: Ruda-Cardinal

08/05/2022

Flagstaff Tech Tour, 2022

08/02/2022

2022 CEO Leadership Retreat

08/01/2022

2022 CEO Leadership Retreat

07/27/2022

Thermal Integrity Updates in Ansys 2022 R1 - Webinar

07/20/2022

Simulation Best Practices for the Pharmaceutical Industry - Webinar

07/14/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

NCMS Technology Showcase: Corpus Christi Army Depot

07/13/2022

Additive & Structural Optimization Updates in Ansys 2022 R1 - Webinar

07/07/2022

Arizona AADM Conference, 2022

06/29/2022

LS-DYNA Updates & Advancements in Ansys 2022 R1 - Webinar

06/23/2022

Simulation Best Practices for Wind Turbine Design - Webinar

06/15/2022

MAPDL Updates & Advancements in Ansys 2022 R1 - Webinar

06/01/2022

Mechanical Updates in Ansys 2022 R1 - pt. 2 Webinar

05/26/2022

Modelling liquid cryogenic rocket engines in Flownex - Webinar

05/25/2022

SMR & Advanced Reactor 2022

05/25/2022

05/24/2022

SMR & Advanced Reactor 2022

05/19/2022

RAPID + tct 2022

05/19/2022

Venture Cafe Roundtable: AI & Healthcare

05/18/2022

Tucson after5 Tech Mixer: World View

05/18/2022

RAPID + tct 2022

More Info

05/18/2022

Signal & Power Integrity Updates in Ansys 2022 R1 - Webinar

05/18/2022

Simulation World 2022

05/17/2022

RAPID + tct 2022

05/11/2022

Experience Stratasys Manufacturing Virtual Event

05/04/2022

Mechanical Meshing Updates in Ansys 2022 R1 - Webinar

04/27/2022

04/22/2022

12TH ANNUAL TUCSON GOLF TOURNAMENT

04/21/2022

04/20/2022

Additional Fluids Updates in Ansys 2022 R1

04/20/2022

Experience Stratasys Tour – Tempe Arizona

04/18/2022

Experience Stratasys Tour - Flagstaff Arizona

04/14/2022

D&M West | MD&M West

04/13/2022

D&M West | MD&M West

04/13/2022

Experience Stratasys Tour - Albuquerque New Mexico

04/12/2022

D&M West | MD&M West

04/12/2022

Experience Stratasys Tour - Los Alamos New Mexico

04/12/2022

Optimizing Engineering Workflows f​​​​or Propulsion System Design

Search in PADT site

Contact Us

Most of our customers receive their support over the phone or via email. Customers who are close by can also set up a face-to-face appointment with one of our engineers.

For most locations, simply contact us: