Engineers at Honeywell Engines and Systems used CFD in an effort to minimize the number of test rig configurations necessary for the design of turbofan mixer nozzles from an average of three to one. These lobed mixer nozzles help to improve engine performance by maximizing gross thrust by 1-2 percent at cruise conditions, and minimizing peak exhaust velocity to reduce noise, particularly during take-off. Mixer nozzles work by introducing cooler fan air through an annular lobed structure to mix with the hot core flow from the turbofan engine exhaust. Mixer nozzles can help reduce the engine thermal signature, an important functionality to military engine designers.

Honeywell rig hardware

Honeywell's CFD analysis of the mixer nozzle utilized the full range of FLUENT's CFD tools from the RSM turbulence model to unstructured meshes to grid adaption. A systematic approach for validating FLUENT for this application was developed by the engineers. In this process, the FLUENT predictions agreed well with test rig measurements. In particular, very good estimates of nozzle efficiency and a reasonable estimate of nozzle f low capacity were obtained. In addition, the engineers gained insight using CFD that they could not have obtained from the test data.

CFD simulations were performed to match the rig hardware dimensions

Mixer nozzle temperature contours

The fact that only one rig was constructed allowed the engineers to meet aggressive mixer nozzle design goals in a single design cycle. Elimination of redesign costs reduced overall costs for this project by an order of magnitude. This combined CFD/test rig data approach is now standard at Honeywell for mixer nozzle designs.

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