Coupling ANSYS Mechanical and Flownex

The below example demontrates how to couple Flownex and ANSYS mechanical using the Mechanical Generic Interface component.

For those that don’t know, Flownex is a thermal-fluid system modeling tool that is great for modeling heat, flow, pressure, etc… in systems.  At PADT we often connect it to ANSYS Mechanical to do more detailed component level simulation when needed. 

Why the need for the link in the fist place?

  • It is an automated workflow to couple Flownex and ANSYS through direct mapping of Flownex results (HTC and bulk temperatures) as boundary condition to an ANSYS thermal analysis.
  • Represents a conjugate heat transfer model with fluid calculations handled in Flownex
  • Allows one to easily/quickly investigate fluid flow and heat transfer properties under a wide range operating conditions.

First we will discuss the steady state thermal ANSYS Mechanical model that will be linked to Flownex.

We have a pipe Pipe with arbritraty geometry and material properties. Convection boundary conditions have been applied to both the internal and external pipe walls. The inernal Bulk Temperature will be supplied by Flownex.

  • External BC
    • HTC 100 w/m2K
    • Bulk Temperature 22C
  • Internal BC
    • HTC 1500 w/m2K
    • Bulk Temperature will be supplied by Flownex

A command snippet, which will calculate the total heat flow through the inner wall surface and write the value out into a text file called d_result, has been inlcuded in the ANSYS Mechanical model.

In order to achieve a bidirectional coupling, Flownex will execute the Mechanical APDL batch file. We can generate the Mechanical APDL batch file (ds.dat), from within Mechanical.

The soluiton procedure is as follows

  1. Flownex modifies the ds.dat file
  2. Flownex executes the modified ds.dat file
  3. The modified ds.dat file generates the d_result.txt file
  4. Flownex reads the d_result.txt file
  5. Flownex executes an iteration, using value from d_result.txt
  6. Repeat untill solutions are converged.

The next step after creating the ds.dat file is to set up your Flownex model.

The Flownex model comprises of a pipe component with arbritrary geomery, filled with air with an inlet temperature and pressure of 500˚C and 120 kPa respectilvy and a flow rate of approximatly 1kg/s.

We have connected the pipe component to the Mechanical Generic Interface using data transfer links.

The data transfer links pass the bulk fluid temperature form the pipe to the Mechanical Generic Interface component, and return the heat flow value calculated using ANSYS to the pipe.

Next we need place the ds.dat file in the AnsysMechanical_Files folder which is located in the Flownex project folder. It is necessary to create a copy of the ds.dat called ModifiedData.dat in the same location.

Let’s go over the inputs to the Mechanical Generic Interface component in Flownex:

1) Executable location

C:\Program Files\ANSYS Inc\v180\ansys\bin\winx64\Ansys180.exe

This is the path to ANSYS executable. Pay particular attention to the version number (eg 180, 172), as this will be different depending on the version of ANSYS you have installed.

2) Command line parameters

-b -i ModifiedData.dat -o results

Flownex will launch ANSYS, and execute the ModifiedData.dat Mechanical APDL batch file from the command line, using the above command a detailed description of command line options can be found in another blog post here.

3) Project files folder, Data file name and Modified data file name

Here we specify location of the Mechanical APDL batch files

4) Inputs

Here we will define where in ModifiedData.dat the value from Flownex, fluid temperature in this case, will be placed. This is done by determining what the boundary condition variable and ID is, and finding the prefix before the boundary condition value in the ds.dat file. Typically the variable for temperature is _loadvari and for HTC it is _convari.

It is possible to know the boundary condition ID by activating the appearance of Beta options in WB.

5) Outputs

Here we will specify the location of the d_result.txt that ANSYS generates. It should appear in the same folder as the Mechanical APDL batch files after successful execution.

Flownex and ANSYS will pass data back and forth every time step of a transient Flownex run.

The simulation should continue to run up to, and beyond the point where the Flownex and ANSYS simulation have converged. If we plot out the heat input or temperature value vs time we should be able to visualize convergence, akin to residual plots when running a CFD simulation, and then manually stop the simulation after values have stabilized.

Below we increase the fluid inlet temperature form 500˚C to 1000˚C after 10 iterations, and observed a increase in heat flow from ~1.4kW to ~2.8kW.

Major Enhancements in FLOWNEX 2015: Combustors, Importers, and Pipes

FlownexLogo_OfficialSimulation has revolutionized flow and heat transfer dependent systems over the past decades by minimizing costly physical testing and accelerating time to operation around the world. But for many companies, such simulation has largely focused on components and proved to be very time consuming. The technology advancements delivered by Flownex SE now offer a fast, reliable, and accurate total system and subsystem approach to simulation.


With the release of FLOWNEX 2015, users now have access to advanced combustor system level modeling and they can interact with more system and component simulation tools. This is on top of the already considerable capabilities found in the  tool

Gas Turbine Combustor Heat Transfer Library

During the Preliminary design phase or when considering modifications to existing combustor designs it’s essential to make realistic predictions of  mass flow splits through the  various air admission holes, total pressure losses liner temperatures along the length of the combustor etc.

FLOWNEX-2015-combustor-simulationAlthough very powerful, 3D CFD solutions of combustors are specialized, time consuming processes and therefore are seldom exclusively used during initial sizing of a combustor.

It has been demonstrated that 1D/2D network tools, like Flownex, are capable of predicting with reasonable accuracy the same trends as more detailed numerical models.

The advantage, however, is Flownex’s rapid execution, which allows design modifications and parametric studies to be conducted more simply than ever before. The ease of use and incredible speed of Flownex allows 1000s of preliminary designs to be evaluated under all modes of operation for steady state and dynamic cases. Furthermore, the data obtained from the one-dimensional analysis can be used as boundary conditions for a more detailed three-dimensional model, ultimately supplementing a typical combustor design work flow.

While the simulation of combustor systems was previously possible in the Flownex environment, much of the work of implementing industry standard heat transfer correlations was left to the user through scripting .Now in Flownex SE 2015 it’s all been built in to the tool, while maintaining the flexibility required to model any combustor configuration.

New components include

  • Film convection component
  • Fluid radiation component
  • Jet impingement heat transfer component

To sum up Flownex allows more accurate initial designs, less time is spent on advanced 3D combustor simulations and rig tests, thus reducing development time and cost.

Here is a Video that shows off these features:

Added importers and integration features

AFT Fathom/Impulse/Arrow importer

An importer was added to import the file formats of AFT products. The importer imports all the diameters, loss factors heights, etc. so 90% of the effort is done, and in some cases the networks solve without any modifications.

ROHR2 Integration (pipe stress analysis software)

Flownex has the ability to calculate forces during dynamic simulations. This is very useful in pipe stress analysis for surge or water hammer cases. The ability to import complete geometries from ROHR2 and export results in the format that ROHR2 expects natively has been added. This means a user can perform these combined analysis now with ROHR2 with the minimum of effort.

Fluid Importers

An Importer was added to import liquid and gas properties from CoolProp an open source fluid property library. The existing Aspen/Hysys fluid importer was changed to be a generic Cape-Open compliant importer. This means that fluid properties can now be imported from any Cape-Open compliant server software.