A CFD Investigation of the Two Phase Flow Regimes Inside the Bearing Chamber and De-aerator of a Jet Engine

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Virginia Tech

In a jet engine air and oil are mixed during removal from the bearing chamber. Before the oil can be recycled back into the system it must be separated from the air. This is accomplished through use of a de-aerator and breather. The oil air mixture enters the de-aerator first. The de-aerator is a vertical cylinder in which the air and oil enter from the top of the system. Gravity then pulls the oil down as it circulates along the outer wall of the de-aerator. The air is forced out through a top hole and sent to the breather where any oil droplets which remain are furthered separated. A pedestal is located near the bottom of the de-aerator. The pedestal creates a gap between itself and the de-aerator wall. Ideally this gap should be large enough to allow oil to flow through the gap without pooling on the pedestal, but small enough so that air does not flow through the gap. The oil will pool up on the pedestal and reduce the efficiency of the system. In this research, a 30° conical pedestal with a gap of 10.7% was tested. The results showed that the pedestal gap of 10.7% is too large and allows air to flow through the gap. The maximum water was 8.5% and the average water thickness was 5.11%. After studying both the previous experimental data and current CFD data, it is recommended further testing be conducted on pedestal gaps between 8.5% and 9.5%.

Jet Engines, Turbine Lubrication, Oil and Air Separation