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Underdeveloped airflow in ducting systems is an area that has not been researched heavily. There is little information and data about turbulent, underdeveloped flow available, so there is no sure way to check to find static pressure drops in complex ducting systems. The Boeing Company has to physically build and test each ducting network that is used in their airliners. This process is tedious and expensive so they wish to have some calculated pressure drops and loss coefficients for certain geometrical models.

Computational Fluid Dynamics (CFD) software was used for the majority of the testing and calculations. An experimental setup was designed and studied in conjunction with computational models in order to provide the data necessary to develop correlations between static pressure drop and flow velocity through air distribution system components found in the cabins of typical airplanes. The models that were tested in this project include 90° bends and gradual expansions followed by sharp edge branched orifices. After much research had been completed, the sponsor requested that inline orifices also be studied.

The main goal of the project was to develop tables and graphs that give correlations for the various experimental setups. The main factor influencing the pressure drop and loss coefficient values was the orifice diameter, so many variations on the diameters were tested. The experimental test setups were constructed in order to compare and verify with the CFD results. An example of one of the graphs can be seen in the figure to the left.

Most of the research for data collection was done using CFD software. Each model was constructed in GAMBIT and tested in FLUENT, which is the same software that is used by Boeing. There were many variations that could be tested so the team decided to narrow our focus to a few geometries.

Bends

A 90° bend followed followed by an orifice was the main model tested. The following parameters were used for the models:

Main diameters: 3,6,9, and 12 inches
d/D ratios: .25, .3125, .375, .4375, .5
Velocities: 1000, 3000, and 5000 feet per minute (fpm)
Length after bend to orifice: 3, 6, and 12 inches

Other variables tested such as length after orifice did not have significant effects on the static pressure drop and thus were held constant. This data was used for the branched orifice testing, but due to time constraints the parameters tested were narrowed for the testing of the inline orifice based on results of the branched testing.

This model involved a gradual expansion followed by an orifice. The included cone angle was kept at a constant 32° as a worst case scenario for noise. The following parameters were used for the models:

The d/D ratio involved the larger main duct diameter since the orifice was placed in this part of the duct.

An experimental test setup was constructed to operate under conditions specified by Boeing to compare and verify the CFD results. The team chose to use PVC as its sample ductwork material due to its smooth finish. A digital anemometer was used to measure the airflow velocity from the test system. A manometer was used to calculate the pressure drops. The following parameters for the test setup were deemed necessary by the group:

The results varied slightly from those calculated in the CFD software due to a variety of reasons. First it was difficult to create the effect where the two pieces were jointed in CFD, and secondly, the blower couldn't match the velocity needed when the ducting system became large. It was very difficult to construct a perfect match of the ducting system and therefore difficult to obtain reliable results.