Simulations are a key technology in the aviation industry

Simulation techniques are transforming development and production—including in the aviation industry. Virtual manufacturing makes processes faster, more efficient and more cost effective.

05.2016 | Text: Monika Weiner

Text:
Monika Weiner has been working as a science journalist since 1985. The geologist is especially interested in new develop­ments in research and techno­logy, and in their impact on society.

Every nick costs money. If an engine is to operate at maximum capacity, the sur­faces of the turbine components must be smooth as glass. When you consider that compressed air is flowing over the surface at speeds of up to several hundred kilo­meters per hour, even the tiniest imperfections cause disruptive turbulence. Manu­facturing blade-inte­grated disks, or blisks for short, also calls for ultimate precision. Cutting out a component with such a complex geometry from sheets of titanium a meter across is a real challenge. “Even the smallest of vibrations in the cutting head leave tiny scores in the surface, which can be remedied only with time-consuming post-processing. In the worst case, the whole blisk is unusable and you’re left with scrap that cost the same as a small car,” says Thomas Dautl, head of the manu­facturing tech­nologies department at MTU Aero Engines.

The chatter marks left by the cutting machine are a problem he has been grappling with for years. “Some blisks were affected, others not—and nobody knew exactly why.” It took the simula­tion experts to get to the bottom of the puzzle. With the help of computer models, they discovered that the rotation of the cutting head can trigger resonances in the titanium sheet. Tiny differences in the geometry and composition of the sheet are all that decides whether it begins to vibrate and divert the cutting head from its pro­grammed course. The simula­tions were also able to uncover how to prevent the unwanted vibration, for instance by fitting damping elements or altering the pro­cessing speed. Pro­duction implemented the recom­men­dations and suddenly the problem of chatter marks was eliminated.

Key technology for the aviation industry

Computer programs instead of trial and error. The routine applications of simula­tion technology in the aviation industry are numerous: Optimizing air­craft aerodyn­amics; cutting fuel consump­tion; reducing noise pollution; increasing safety; and making material selection and production processes more efficient. “Numerical simulation is a key technology for the aviation industry. Simula­tions are irre­place­able in developing engines and air­craft, optimizing them and getting them to market quicker,” says Dr. Edmund Kügeler, head of the numerical methods depart­ment at the German Aerospace Center’s (DLR) Institute of Propulsion Techno­logy. “The advan­tage of simu­lations over a conventional test bench is that they are cost effective: You can sit at your computer and run through designs and parameters without having to build costly test objects or conduct expensive experiments. Simula­tion and optimization techno­logy provides an auto­mated way to find the best solutions from your computer.”

Video: Comprehensive testing Article with video

Comprehensive testing

The simulation of the additive manufacturing process enables the homogeneity of the metallic ingredients to be tested. To the video ...

MTU has made use of soft­ware tools for years to solve problems with vibrations. Traditionally, though, simula­tions have only been capable of looking at an individual manu­facturing step. “There are specific tools for the various tasks, all varying in their level of detail and mostly incompatible with one another,” notes Thomas Göhler, a specialist in computer-aided analysis in materials develop­ment at MTU. “Since it’s almost impossible to link between the individual simula­tion steps, important information is lost: For instance, the material pro­perties of a titanium sheet are important not only for control­ling the cutting head but for the blisk’s performance, too.”

“There’s no doubt in my mind that simulation techno­logy has a lot more to offer than we have utilized to date,” agrees Dr. Andreas Fischersworring-Bunk, head of materials and damage modeling. “We could boost the efficiency of engine building enormously if only we could find a way to model and optimize the entire manu­facturing process from materials develop­ment through to final testing.” In pursuit of this goal, he is working together with an inter­disciplinary team on a new, cross-system approach.

Video: Numerical Methods Article with video

Numerical Methods

Flow in compressor Rig 250 To the video ...

Linking together the results from individual simula­tions

The answer may lie in a new ap­proach going by the name of ICM2E, short for Integrated Computational Materials and Manu­facturing Engineering. Researchers around the world are using this still new method to optimize materials develop­ment and manu­facturing by linking together the results from individual simula­tions. Their goal is to coordinate all the parameters from materials develop­ment through the entire pro­duction pro­cess so as to obtain a finished part that has exactly the desired pro­perties.

In order to adapt the ICM2E concept to the require­ments of MTU as an engine manu­facturer, Thomas Göhler and his team had some pioneering ground to cover. The fruits of their labor can be seen on the screen in the materials specialist’s office, where a virtual laser beam is racing over virtual metal powder. Tiny blue granules melt and fuse together, punctuated by the odd red spot—tiny inhomogeneities just micrometers in size. A component takes shape layer by layer. Too slow? Göhler clicks with his mouse and the speed doubles. Now, though, you can see bigger red spots, inclusions where the powder has not fused properly. Thanks to a new simula­tion tool developed by Göhler’s team in collaboration with researchers from the Fraunhofer Institute for Mechanics of Materials IWM, it is now possible for the first time to see the impact of laser energy and speed on a material’s properties. Doctoral student Tobias Maiwald-Immer then takes the granule size and error rate determined in the course of the simula­tion and exports it into the next piece of software, which visualizes the material’s structure. Now you can see how the crystals grow: “By combining the various simula­tion tools, we can demonstrate for the first time how manu­facturing para­meters during laser sintering impact a material’s strength and elasticity,” says Göhler.

Numerical simulation Simulation of the pressure acting on a passenger airliner during the landing approach.

Machine setup based on the computer model

The component we saw taking form on Göhler’s screen actually does exist; MTU already series manu­factures the bore­scope boss using selective laser sintering. The optimum machine settings came from the computer model. “A comparison with physically manu­factured materials indicates that the simula­tion predictions correlate with the actual results obtained during laser sintering,” says Fischers­worring-Bunk.

It is just as much a success for project partner Dr. Dirk Helm, who heads the Manu­facturing Pro­cesses business unit at Fraunhofer IWM. “In this project we have laid the groundwork for the industrial application of ICM2E and demonstrated what the approach can achieve. The simulation makes it very clear how small changes in the process chain affect material properties. This means we can accurately deduce the manu­facturing para­meters required to pro­duce a component of extremely specific pro­perties.”

(strich:Computer simulation) of vortexes generated by helicopter rotor blades. Hover over the image for a bigger view

Computer simulation of vortexes generated by helicopter rotor blades.

1-hubschrauber

Computer simulation of vortexes generated by helicopter rotor blades.

(strich:Numerical simulation )of ­aerodynam­ic flows acting on an Airbus A380. Hover over the image for a bigger view

Numerical simulationof ­aerodynam­ic flows acting on an Airbus A380.

2-A380

Numerical simulationof ­aerodynam­ic flows acting on an Airbus A380.

(strich:Simulation) of the temperature distribution in a two-stage low-pressure turbine. Hover over the image for a bigger view

Simulation of the temperature distribution in a two-stage low-pressure turbine.

3-Temperatur

Simulation of the temperature distribution in a two-stage low-pressure turbine.

(strich:Simulation) of turbulence effects on a two-stage low-pressure turbine. Hover over the image for a bigger view

Simulation of turbulence effects on a two-stage low-pressure turbine.

4-Turbulenzen

Simulation of turbulence effects on a two-stage low-pressure turbine.

Now the engineers at MTU want to simulate how the individual manu­facturing steps affect the quality of the final blisk. “It’s a particular chal­lenge since we get the raw materials from external suppliers, who have to be included in the process,” says Fischersworring-Bunk. “Only they can provide the raw data we need to optimize the various processing steps and achieve the per­formance we require.”

Simulation-assisted product and manu­facturing develop­ment

That’s not the end of it: integrated simula­tions can also be used to calculate how long it takes to manu­facture a component, where there are savings to be made and how to run machines at optimum capacity. “Our goal is a simulation-assisted pro­cess of product develop­ment that covers everything—from microscopic material properties through all the stages of manu­facture and all the way to the finished engine,” says Dautl. A Herculean task when you consider that that means factoring in 1,000 components.

Trends in simulation development

Physically based predictions Confidence in evaluation Simulation automation Computing efficiency Multi-discipline analysis and optimization
Goal
Model real interactions rather than simplified correlations. Increasing substitution of experiments with simulations. Accelerate and simplify work processes, multi-user func­tion­ality. Run computing operations simul­ta­neously, efficient handling of increasing quantities of data. Virtual linking of all specialist dis­ci­plines required to develop and manufacture engine components.
Method
Factor in materials’ composition, production process, microstructure, interior defects, mechanical properties, workability and performance in operation. Systematic comparison of results from simulations and experiments. Link simulations that build on each other, automatic evaluations. Further development of hardware and software for faster, simul­ta­neous computation in high-performance computer centers. Virtual linking of all specialist dis­ci­plines required to develop and manufacture engine components.

Simulation in the aviation and its applications

Aircraft Structural mechanics Engine technology
Goal
Cost savings in the devel­opment process. Improved airflow for fuselage and wings; reduce air resistance; prevent turbulence. Cost savings in the development and testing of new materials; modeling of composite materials’ capacity. Cost savings in the development process. Improved material properties; high-performance, quiet and extremely efficient engines.
Appli­cations
Aerodynamic simulations help to optimize the aircraft’s shape and so minimize air resistance and fuel consumption. Simulations allow researchers to calculate the form and stability of new, weight-saving composite materials. Simulations allow for the optimization of both individual components and complex systems; by selecting the right materials and manufacturing processes, it is possible to guarantee the required component performance and service life.
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