CFD Analysis of Pressure Losses in Flat-Oval Duct Fittings

Headnote

ABSTRACT

This paper is a summary of a study conducted by the team at HVAC design d.o.o. Sarajevo in the framework of the ASHRAE RP-1493 CFD Shootout Contest-Prediction of Duct Fitting Losses. In the introductory section, methods of airflow modeling and simulation used in this analysis are briefly described. This is followed by a presentation of a set of validation results that were used to select appropriate simulation parameters. Next, computational fluid dynamics (CFD) results of pressure loss coefficients in flat-oval ducts and tee and lateral duct fittings at different flow rate ratios and Reynolds numbers in both converging and diverging flow modes are compared to empirical correlations and measurements. Obtained duct fitting simulation results are generally in qualitatively good agreement with laboratory data.

(ProQuest: ... denotes formulae omitted.)

INTRODUCTION

This paper discusses a computational fluid dynamics (CFD) analysis of pressure losses in flat-oval duct fittings that was performed in the framework of the ASHRAE RP-1493 CFD Shootout Contest-Prediction of Duct Fitting Losses (ASHRAE 2010). The aim of the contest was to assess predictive performance of CFD with respect to calculation of pressure losses in tee and lateral flat-oval duct fittings at a range of flow rate ratios and Reynolds numbers for both converging and diverging flow modes without reference to experimental data. Additionally, the competition was designed to estimate to which extent CFD methods are capable to substitute the often expensive measurements procedures for determination of loss coefficients and calculation of pressure losses in complicated duct fitting systems.

Contest Test Cases

Figure 1 shows sketches of the duct fittings studied. Major and minor dimensions of the main duct are denoted as A and a, respectively, while the corresponding dimensions of the branch duct are denoted as C and c. The dimensions are taken from ASHRAE RP-1493 (2010) as

A = 787 mm (30.98 in.)

a = 356 mm (14.02 in.)

C = 559 mm (22 in.)

c = 254 mm (10 in.)

The hydraulic diameter of a duct is defined as A

...

For the two duct sizes of the fitting the hydraulic diameters are

D^sup large^^sub k^ = 511 mm (20.12 in.)

D^sup small^^sub k^ = 364 mm (14 33 in )

where superscripts large and small denote main and branch ducts,...