The aerospace industry is driven more than ever to reduce time and cost of developing new aircrafts while reducing weight without compromising performance.  This challenge cascades down to design of aircraft engines, where engines manufacturers are striving to deliver higher fuel efficiency and higher power per unit weight of an engine. The challenge cascades down further to aerospace systems suppliers.  Aircraft engine gearboxes is one such aerospace system.  The focus of this paper is to addresses the challenges of designing aircraft engine gearboxes through application of model based systems engineering and a design workflow based on simulation and optimization.

 

A typical gearbox design starts with system level performance requirements such as power requirements, speed, torques and operating conditions.  The goal is to design a minimum weight gearbox in the shortest possible time that meets all the performance requirements.  In this paper, authors present a design workflow developed for meeting that goal. The steps of this workflow are as follows.

 

1.      Application of model-based systems engineering to generate a driveline concept to meet the system performance requirements.  Output of this step, such as gear and bearing loads will be used as an input to Step 4 of structural optimization.

2.      Generation CAD geometry of inner mold line of the housing around the gear train obtained from Step 1.  Also generate CAD geometry for oil inlets and outlets.  These will be used as input to the next two steps.

3.      Design studies using computational fluid dynamics (CFD) to minimize the amount of oil needed in the gearbox.  Potential design parameters include, but not limited to, number of oil inlets and outlets, location and orientation of oil inlets, inlet velocities, inner mold line geometry and so on.  The CFD simulations may also be coupled with thermal analysis to predict thermal loads on the housing. The software used in this step is a state-of-the-art CFD tool based on smooth particle hydrodynamics (SPH) formulation.  Additionally, it leverages compute power of Graphics Processing Units (GPU), which makes it feasible to perform design studies.

4.      Structural optimization of gearbox housing to obtain a minimum weight housing design starting with the inner mold line geometry.  This is done in three steps: (i) topology optimization to generate a concept design, (ii) design interpretation, and (iii) design validation and refinement.  Design performance targets may include, but not limited to, stresses, fatigue life, vibration and noise. This three-step optimization process is proven to deliver lightest possible structures while minimizing the design time and meeting performance requiremens.

5.      Manufacturability assessment of the housing.  Gearbox housings are typically manufactured using castings.  So, in this workflow authors have used simulations for assessing castability of housing.  An advanced casting feasibility technique is used which performs castability simulations a couple of magnitude faster than other tools used for casting process simulations. 

 

Each step in the above process uses advanced technologies to make each step significantly faster than before.  Additionally, the process offers a seamless transition of data form one step to the next using a common digital thread.  This, in turn, offers another level of efficiency in design time.  The workflow can be further expanded by introducing additional simulations such as external CFD or material design.  Those could be future topics of development.  Also, this workflow does not address challenges of gear and bearing design.  A separate workflow is needed to address those design challenges.  The current workflow focuses on design of housing and lubrication. This workflow is demonstrated on an aircraft engine accessories gearbox.  This process is equally applicable to designing any aerospcae gearbox.


Simulation Driven Design Workflow for Aircraft Engine Gearbox

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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