1. An Investigation into the Effects of Turbofan Aircraft Nacelle Placement on Aircraft Drag
Philip Brown (Y3292943)
Introduction
Aim
The aim of the project is to analyse the drag characteristic of three different configurations of
engine nacelle placement (under-wing, in-wing and over-wing) on the Boeing 737-800 wing. This
is in order to determine which configuration provides the greatest efficiency with respect to drag.
Background
Modern large passenger aircraft strive to be as efficient as possible, be it in use of materials,
engine management systems or bigger aircraft. One thing that hasn’t changed is the placement of
aircraft engine nacelles.
Current large passenger aircraft tend to have their engines below the wing. It is common for
smaller passenger jets to have their engines placed behind and above the wing and this can be
seen in designs currently in use by companies such as Bombardier and Gulfstream. In-wing
nacelles tend to only be seen on older aircraft such as the DeHavilland Comet and the BAe
Systems Nimrod.
Method
The project took in three different methods of determining the drag of a Boeing 737-800 wing.
These were:
 Flat Plate Approximation
 2D Aerofoil Sections simulated with OpenFOAM’s SimpleFoam solver.
 A full 3D wing section simulated with OpenFOAM’s SimpleFoam solver.
2D Aerofoils
A Boeing 737 wing is made of 4 different aerofoil sections and so to give a good idea of drag, we
can determine the coefficient of drag of each section and then by using the standard drag formula
(D=½ρv2
SCD), we can determine the drag of each section from a simplified model of the wing.
Results
Flat Plate Approximation
The clear winner in this approximation is the in-wing setup, mostly due to the fact
that flat plate approximation is approximating only the skin friction. The in-wing
setup has less surface area and therefore we would assume that it would have
the least skin friction drag.
2D Aerofoils
This time, the under and over-wing configurations have the lower drag, largely
probably due to nacelle aerofoil choice for the author . If this was re-run with a
more supercritical aerofoil, this may have been in the in-wing configuration’s
favour.
Full Wing
The hope of the author was to investigate the interactions of fluid flow around
the nacelle and wing to see if one of the configurations would come out with the
most favourable drag profile. Unfortunately, with the time constraints placed on
the project, the author didn’t manage to complete this.
2D Aerofoil Velocity Maps
Drag Profiles
Flat Plate Approximation
2D Aerofoils
Conclusion
Unfortunately, there was not enough time to get a definitive answer on
which wing configuration was the most efficient from a drag point of view.
With more time, all three of the wing configurations could have been tested
fully to give us a better answer.
Continuation
There are many ways to improve on this project, eleven of which are in the
main body of the project. Just a few of them are below:
Structural Analysis of the wing
Ground-Air-Ground (GAG) Cycle Modelling
Nacelle Pylons
Runway Debris
Stability Issues
Turbine Disc Burst Damage
Design Alteration Costs
Maintenance Inspection
Vibration Transmission
Computational Aeroacoustic Modelling
References
Elizabeth, D.(2012) Passenger Airplane Wallpaper [Photo] [Online] Available at http://www.desktopwallpapers4.me/aircraft/
passenger-airplane-5616/ (Accessed 31st August 2013).
OpenCFD Ltd (ESI Group) (2013) OpenFOAM –The Open Source CFD Toolbox (Version 2.2.0) [Computer Program] Available at
http://www.openfoam.com/ (Accessed 11th
February 2013).
Geuzaine, C.and Remacle, JF (2013) GMsh (Version 2.8.2) [Computer Program] Available at http://geuz.org/gmsh/ (Accessed 20th
March 2013).
Kundu, P.K. and Cohen, I.M. (2008) Fluid Mechanics, 4th edn. United States of America, Academic Press.
Flat Plate Approximation
As a first point of call, determining drag forces from just the skin friction of the wing surfaces, can
give an idea of which nacelle configuration is most efficient. This is where the flat plate
approximation comes in. Using the formula CD=1.33÷√Re, we can determine the coefficient of
drag and thus the total drag of each nacelle configuration.
Full Wing
As mentioned above, the Boeing 737 wing is complex and so a 2D aerofoil will not be able to fully
provide all sources of drag. We must therefore create an as faithful as possible representation of
the wing. Through OpenFOAM, we can determine the drag of each configuration directly with
reasonable fidelity.
Root Aerofoil
Aerofoil C
Aerofoil B
Tip Aerofoil
Nacelle Aerofoil
Config Wing Nacelle Pylon Total
Drag/ N
Re Cd D/ N Re Cd D/ N Re Cd D/ N
Under 26571546 0.00025801 387.35 22142955 0.00028264 65.20 22142955 0.00028264 32.32 484.87
Over 26571546 0.00025801 387.35 22142955 0.00028264 65.20 22142955 0.00028264 32.32 484.87
In 26571546 0.00025801 359.72 26571546 0.00025801 26.08 0 0 0 385.80
Config Total Drag/NSection Drag/N
1 2 3 Nacelle
Under 8500.4 7996.5 6934.5 41405.6 64,837
Over 8500.4 7996.5 6934.5 41405.6 64,837
In 7867.0 4622.9 6934.5 80514.4 99,939
Drag Tables
Flat Plate Approximation 2D Aerofoils