A rib valve is under consideration for use as a shutter in an air swirler in the fuel nozzle of a variable-geometry combustor. In the original application, the variable-geometry combustor would be part of an engine in the High-Speed Civil Transport. In this application, the rib valve/shutter would provide the variable-geometry airflow needed for proper functioning of the combustor under various operating conditions, including rich burn, quick quench, and lean burn. In this context, "proper functioning" means not only smooth and efficient operation but also minimization of quantities of harmful exhaust gases. The rib-valve and variable-geometry combustor design might also be adaptable to any future gas turbine engines.
The rib valve is built into the air swirler (see figure). The air-swirler vanes are mounted in a stationary subassembly. The ribs are straight blades that are located between the air-swirler vanes and are mounted in another subassembly that can be moved axially to insert the blades between the vanes or withdraw the blades from between the vanes. When the blades are fully with
drawn, the air flows axially into the swirler, with very little obstruction— almost as though the blades were not present. When the blades are inserted all the way, the passages between the vanes are blocked, shutting off the flow of swirling air. Flow conditions between these extremes are obtained by moving the blades to intermediate positions.
The rib valve offers advantages over a block valve that is similar except that (a) throttling is effected by an annular disk, the axial position of which can be adjusted to obtain various degrees of partial blockage of the inlet to the air-swirler-vane subassembly and (b) as a consequence, air enters radially, then turns to flow axially. The effective opening area of the block valve in the fully open position is about 10 percent less than that of the rib valve in the fully open position; as a result, the pressure loss in the block valve is almost 20 percent more than that in the rib valve.
One of the consequences of the rib-valve design is that the velocity of the airflow is nearly uniformly high across the radial flow gap. This is an advantage in that high velocity is needed for adequate atomization of fuel near a fuel filmer in the nozzle. In the block valve, the velocity is low near the fuel filmer, and the flow profile is skewed when the valve is half open.
This work was done by Qiang Wang of United Technologies for Lewis Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Lewis Research Center
Commercial Technology Office
Attn: Tech Brief Patent Status
Mail Stop 7-3
21000 Brookpark Road
Refer to LEW-16033.