Mechanical loads on a turbofan engine structure at blade-off

Abstract: Aircraft engine development is an expensive and time consuming business. The
engines have to be designed to withstand loads well above those encountered
during normal operating conditions. To meet the certification requirements
manufacturers conduct tests where the engines are subjected to extreme
conditions and loads. One such extreme condition is fan blade-off (FBO).

Using finite element methods (FEM) computational software one can simulate
FBO conditions and predict what loads it will inflict on the engine
structure. These simulations involve large models that contain many degrees
of freedom. As such they are time consuming to create and evaluate. Also they
demand a detailed knowledge of the engine geometry to create.
In preliminary design studies of engines there exists a need for knowing the
loads an engine is subjected to. This provides the design team with valuable
information that is used in decisions regarding engine architecture.

The aim of this thesis is to create a scaled-down, simpler model of a
turbofan engine, that can be used to predict bearing and engine mount loads,
for a fan blade-off event. In addition the model can be used to estimate or
check other parameters like weight and to compare different engine
architectures.

The turbofan model created was based on rotor dynamics, this model was
created in MATLAB and DyRoBeS rotor dynamic simulation software. The
simulations were done on three turbofan engines: a reference engine to
validate the turbofan model and later applied on two proposal turbofan
engines for the coming Next generation Single Aisle (NSA) aircraft.

The results for the simulations show that the turbofan model can be used in
the conceptual design stage. It can provide the design team with an initial
estimate for bearing and engine mount loads. Taking into account the
simplicity of the turbofan model, a conclusion on the accuracy of the results
is that they are within acceptable limits.