Prediction of duct fitting losses using computational fluid dynamics: Fid-Bau Portal

Prediction of duct fitting losses using computational fluid dynamics

Manning, Andy / Wilson, John / Hanlon, Nate / Mikjaniec, Travis

This article outlines a study to evaluate the feasibility and accuracy of using computational fluid dynamics techniques to numerically determine the loss coefficients for duct fittings. The success of the study may eliminate the need of laboratory fitting tests in compliance with ASHRAE Standard 120 (2008) and further facilitate the design process of duct and HVAC systems. In this article, computational fluid dynamics software was used to calculate the loss coefficients for two duct fittings, a flat-oval straight-body lateral and a flat-oval straight-body Tee. Two loss coefficients, namely C_s (main loss coefficient) and C_b (branch loss coefficient), were calculated for each fitting for both converging and diverging airflows at various flow splits and flow rates, with flow velocities in the main and branch sections ranging between 6 m/s and 20 m/s (1181 fpm and 3937 fpm). The configurations modeled replicated experimental test apparatus in compliance with ASHRAE Standard 120. The numerical simulation effort was made as part of a competition blind study, with the experimental results unknown to the authors until its conclusion. The experimental and numerical results are compared here for completeness and to assess the feasibility and accuracy of the computational fluid dynamics software. Due to the nature of the blind study and the experimental methodology used, direct percentage comparison of the results is not possible in this case. However, comparison of the experimental and numerical results show the same structural shape for seven of the eight cases and magnitude agreement for six of the eight cases, indicating that computational fluid dynamics could be used as an appropriate means to model the different configurations.