Curriculum Vitae ~ Michael Farrow

 

MEng Aerospace Engineering Graduate

University Projects

 

Personal Research Project - Wing Embedded Engines for Large Blended Wing Body Airliners - A Computational Analysis

Note: This is a general summary of the project, and has been greatly simplified. For a copy of the full investigation, please download the pdf [Caution, this file is 6.84Mb, you may wish to right click, and save the file instead of opening it in your browser].

On the 26th of June 2009, I was awarded the Len Weaver Memorial Prize by the University of Surrey, for work on this project. The prize is awarded to 'the final year student who demonstrates exemplary achievement in a project related to production engineering, design for manufacture or computer aided production.'

Following directly on from the MDDP Project, my final year personal research project focused directly on the effects of engine placement in Blended Wing Body (BWB) airliners. The design brief was to use Computational Fluid Dynamics (CFD) to compare podded (nacelle & pylon mounted) engines and internally embedded engines, for a test aircraft, modelled on the Boeing/NASA BWB Concept.

The first part of the project involved careful construction of a detailed CAD model of the BWB aircraft, reconstructing dimensions from known aerofoil sections and public domain photography/drawings.

Reconstructed BWB Geometry

Once geometry had been created a detailed drag estimation was performed, in order to analyse thrust requirements for the aircraft. With this in hand, detailed powerplant model was created, using a scaled GE90-115B, so that required engine size could be accuratley estimated. This allowed to conceptual engine placements to be designed and investigated. The podded case, modelled on the BWB 450, and a new embedded case, based upon the Avro Vulcan and Handley Paige Victor type configuration.

Two Experimental Engine Configurations for a BWB Airliner

All three experimental cases were then meshed using AnSYS Icem CFD. Because of time, hardware and complex geometry, an unstructured tetrahedral mesh was used, with a prismatic layer grown into the near wall fluid. To reduce meshing and solver time, the problem was assumed to be symmetric, and only half of the aircraft was meshed.

Two Experimental Engine Configurations for a BWB Airliner

Once coarse and fine meshes had been constructed for all three cases, they were solved for a 0.85 Mach compressible flow using Fluent. Results showed a very strong correlation to the mathematical models, but highlighted a number of unforeseen issues with both engine configurations.

Pressure Contours over the clean aircraft configuration

The first of these issues is the normal shockwave forming along the upper surface of the entire surface. This has the effect of greatly modifying the inlet conditions for the three rear mounted engines.

Two Experimental Engine Configurations for a BWB Airliner

The embedded case was also not without problems. The simplistic design of the engines resulted in the formation of an expansion wave at the inboard vertical edge of the square inlet. Although a small issue at first glance, this has the knock on effect of expanding the flow into the inlet, producing a reduction in inlet mass flow of roughly 12%, a serious problem.

Two Experimental Engine Configurations for a BWB Airliner

The presence of the unfilleted inlet and exhaust manifolds in the surface of the wing was not significant enough to constitute a loss of lift for that wing section. However, the surface intersection between the exhaust manifold and the wing upper surface caused a promotion of the normal body shockwave, effectively accelerating the propagation of the shock.

Pressure Contours Showing Embedded/Clean Normal Shock Comparison

This promotion of the normal body shock will result in early boundary layer separation and a concordant small increase in viscous drag force on the upper surface.

The flow and force data for both cases was then compared, and conclusive results obtained. Although much more research is required to confirm this, it is clear that there are advantages to embedded engines in terms of both pressure and viscous drag. Conversely however, there are significant structural issues presented by such large engines within the structure, and this needs much further investigation.

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