Courtesy of Ray Horstman, Boeing Company

The air control systems group at Boeing recently used FLUENT to redesign a complex mixing manifold on the Boeing 767, realizing substantial savings through the use of CFD.

By demonstrating the effectiveness of the simpler manifold design, the FLUENT analysis saved Boeing more than 75% of the project's cost.

The mixing manifold is part of the passenger cabin ventilation system, in which air for cabin cooling is bled from the compressor in the jet engine, passed through a heat exchanger for cooling, and then expanded to cabin pressure, resulting in a further reduction in temperature. The resulting 25° F air is then mixed with recirculated cabin air and vented back into the cabin. The mixing takes place in the manifold and must achieve a performance requirement of 15° uniformity at the exit.

The redesign effort included a proposal to use complex turning vanes to enhance the mixing of the inhomogeneous air streams. To determine if the vanes would perform as required, a CFD analysis using FLUENT was performed on a model of the manifold that included the proposed vanes. The model contained roughly 80,000 cells. Because the heat loss to the walls was negligible, no heat transfer was considered other than the mixing of the streams. The analysis showed that the turning vanes mixed the streams to within 5° of uniformity, considerably more homogeneity than was required. A separate CFD analysis of a simpler manifold design, without vanes, was then undertaken. This simulation showed that 15° uniformity could be achieved without the vanes, resulting in a simpler design.

The CFD analysis of the mixing manifold took a total of approximately three weeks and resulted in large savings in parts, materials, and tooling by identifying the effectiveness of the simpler design. By avoiding field testing, the CFD work saved additional time and money. In total, Boeing estimates that more than 75% of the project's cost was saved by the FLUENT analysis.

Computational mesh and temperature distribution in the mixing manifold. While the complex vanes in the mixing manifold produced the required mixing, FLUENT showed how a simpler design could be used.

Mesh generation using ICEM CFD.

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