Log in

Login to your account

Username *
Password *
Remember Me

Create an account

Fields marked with an asterisk (*) are required.
Name *
Username *
Password *
Verify password *
Email *
Verify email *

AFT Blog

Welcome to the Applied Flow Technology Blog where you will find the latest news and training on how to use AFT Fathom, AFT Arrow, AFT Impulse, AFT xStream and other AFT software products.
Font size: +
1 minute reading time (250 words)

Using Standard Accuracy Specific Heat Ratio to Solve AFT Arrow Convergence Problems

AFT Arrow is a highly accurate and powerful compressible flow analysis tool and rather than solving various compressible flow correlations, AFT Arrow is simultaneously solving the fundamental mass, momentum, energy, Equation of State, and Mach number equations.  Although AFT Arrow accurately calculates the fluid physical properties throughout the compressible pipe network, there is also a high level of complexity associated with these calculations.

We have seen several models that have various convergence issues and there is a common troubleshooting technique that solves the majority of these issues.  This technique is simply changing the specific heat ratio accuracy option from “High” to “Standard” in the System Properties window.

System Properties Window


By default, the High Accuracy specific heat ratio is used and is defined below as:

High Accuracy Specific Heat Ratio


When the Standard Accuracy option for the specific heat ratio is chosen, an approximation is made such that the specific heat ratio is defined as:

Standard Accuracy Specific Heat Ratio


For superheated gases, this is a very reasonable approximation to make without significant loss of accuracy and thus, is a small change that will help solve a majority of convergence issues.

In order to see if the standard accuracy option is reasonable, compare the fluid properties used in the model with the saturation conditions of the fluid.  If the model predicts pressures and temperatures that are reasonably departed from saturation conditions, then using Standard Accuracy is reasonable.  If model predictions are close to saturation conditions, then high accuracy should be used for the specific heat ratio and other model modifications should be made.

New & Improved Laminar & Non-Newtonian Flow Calcul...
AFT Efforts To Improve Global Presence and Service

Related Posts

 

Comments

No comments made yet. Be the first to submit a comment
Guest
Thursday, 07 July 2022
© 1996 - 2022 Applied Flow Technology