innovation

Nature’s way: Bionics make engines quieter and more efficient

Engineers are developing bionic com­po­nents for tomorrow’s aircraft engines.

02.2019 | author: Monika Weiner | 9 mins reading time

author:
Monika Weiner has been working as a science journalist since 1985. A geology graduate, she is especially interested in new developments in research and technology, and in their impact on society.

Na­ture had sev­er­al bil­lion years to evolve and de­vel­op the per­fect so­lu­tions for its needs. Wood, for ex­am­ple, gets its rigid­i­ty and strength from its cell walls. Bones have a light­weight struc­ture and yet are in­cred­i­bly strong. Reeds have dif­fer­ent lay­ers of cells that make them tough as well as flex­i­ble. And thanks to their struc­tured sur­face, the leaves of the lo­tus flower can re­pel wa­ter and dirt, while shark scales have den­ti­cles that help re­duce drag in the wa­ter.

Ex­am­ples from na­ture such as these have been spark­ing cre­ativ­i­ty and in­spi­ra­tion for hu­man in­ven­tions for years. Even Leonar­do da Vin­ci stud­ied the flight of birds pri­or to build­ing his fly­ing ma­chines—even if his first at­tempts at fly­ing failed be­cause they re­lied on hu­man strength alone to gen­er­ate the nec­es­sary lift. But the con­cept of cre­at­ing lift through propul­sion is still found on­board all air­craft to this day. Fol­low­ing in da Vin­ci’s foot­steps, en­gi­neers to­day al­so take in­spi­ra­tion and ap­ply prin­ci­ples from na­ture when they de­vel­op ma­te­ri­als and com­po­nents.

From development to manufacturing

Additive manufacturing Numerical simulation is used to develop the bionic structure of a component, which is then reproduced in metal by means of additive manufacturing.

Huge innovation potential

Bion­ics, a port­man­teau of “bi­ol­o­gy” and “elec­tron­ics,” has be­come a field of re­search in its own right. As the founder and CEO of Ger­man com­pa­ny die Bioniker GbR and a con­sul­tant at Al­tran Deutsch­land, Markus Holler­mann is a firm be­liev­er in the huge in­no­va­tion po­ten­tial that bion­ics of­fers. “Bion­ics isn’t about copy­ing na­ture but about learn­ing from it—ap­ply­ing its prin­ci­ples to elec­tron­ic prod­ucts and process­es and de­vel­op­ing new func­tion­al­i­ties. Us­ing ex­am­ples from na­ture, we can cre­ate com­po­nents for avi­a­tion ap­pli­ca­tions that are light­weight, ex­cep­tion­al­ly strong and that ab­sorb sound.”

(strich:A bionic component is printed layer by layer) Controlling an additive manufacturing machine. Hover over the image for a bigger view

A bionic component is printed layer by layer Controlling an additive manufacturing machine.

A bionic component is printed layer by layer Controlling an additive manufacturing machine.

(strich:Material-conserving process) Production of a bracket tray. Hover over the image for a bigger view

Material-conserving process Production of a bracket tray.

Material-conserving process Production of a bracket tray.

Bion­ic struc­tures can be used as a ba­sis for lighter, qui­eter and more ef­fi­cient en­gine de­signs—at least the­o­ret­i­cal­ly. For a long time, how­ev­er, this ap­peared im­pos­si­ble to trans­late in­to prac­tice. That’s be­cause con­ven­tion­al com­po­nents are forged or cast, which makes it dif­fi­cult to in­te­grate cav­i­ties or de­signs based on na­ture. But now, ad­di­tive man­u­fac­tur­ing process­es are open­ing up a world of new op­por­tu­ni­ties for de­sign en­gi­neers. A year ago, MTU Aero En­gines formed its own bion­ic de­sign team as part of its Cen­ter of Ex­cel­lence for ad­di­tive man­u­fac­tur­ing.

Head­ed by Dr. Mark Welling, the team has now de­vel­oped a bion­ic com­po­nent: a brack­et for oil lines. Giv­en that the com­po­nent is crit­i­cal to safe en­gine op­er­a­tion, it must meet strin­gent re­quire­ments to ob­tain ap­proval from the avi­a­tion au­thor­i­ties. Un­like the con­ven­tion­al, straight-edged brack­ets that are milled, this new brack­et is curved and takes a shape not dis­sim­i­lar to a bone. “The new de­sign en­abled us to cut the weight of the com­po­nent in half, with­out in­ter­fer­ing with the strength or damp­ing char­ac­ter­is­tics,” says Welling. It’s no co­in­ci­dence that the de­sign re­sem­bles a bone: “Na­ture is ex­treme­ly eco­nom­i­cal; it doesn’t in­vest any more than what is re­quired. If you look at bones, ex­tra ma­te­r­i­al is present on­ly in places where it’s ab­solute­ly nec­es­sary for sta­bil­i­ty. We used a sim­i­lar prin­ci­ple to op­ti­mize our brack­ets—you could say that they’re the re­sult of ac­cel­er­at­ed evo­lu­tion.”

Inside MTU Ideation Challenge Bionic

Na­ture has its own per­fect so­lu­tions—we just have to dis­cov­er them. In 2017, MTU called on em­ploy­ees at all its lo­ca­tions world­wide to take part in the Ideation Chal­lenge and con­tribute their ideas and an­swers to the ques­tions: What can we learn from na­ture that can be ap­plied to en­gine con­struc­tion? And what’s the best way to com­bine bion­ic de­sign with ad­di­tive man­u­fac­tur­ing?

A to­tal of 67 peo­ple sub­mit­ted en­tries on­line, ten of which were se­lect­ed by a team of ex­perts for the next round. The short­list­ed con­tenders then had one last chance to pitch their ideas to a pan­el of man­agers. Fi­nal­ly, the pan­el se­lect­ed three win­ners who were re­ward­ed with the op­por­tu­ni­ty to put their ideas in­to prac­tice.

“The aim of the com­pe­ti­tion was to spark a process of in­no­va­tion,” says Dr. Patrick Holtsch, who helped or­ga­nize the Ideation Chal­lenge. “It’s clear from the re­sults that MTU has a huge pool of ideas with great po­ten­tial at its fin­ger­tips—which we can draw on in our de­vel­op­ment of to­mor­row’s en­gines.”

Ideation Chal­lenge: The win­ning ideas

The bionic borescope
The bion­ic borescope for on-site re­pairs based on the hu­man hand. With its long, thin and flex­i­ble snake-like arm, the borescope can be in­sert­ed in­to the en­gine to in­spect the com­po­nents and smooth the sur­face of the blades, al­low­ing re­pair work to be car­ried out for cus­tomers di­rect­ly on site. The tech­nol­o­gy could help avoid cost­ly and time-con­sum­ing shop vis­its that re­quire the en­gine to be dis­as­sem­bled.

The bionic turbine blade
The bion­ic tur­bine blade—in­spired by the gi­ant reed. With their hol­low stems, these reeds are in­cred­i­bly re­silient and al­so ca­pa­ble of ab­sorb­ing vi­bra­tions. This tur­bine blade has a sim­i­lar de­sign—its hard out­er lay­er and in­ner hon­ey­comb struc­ture make it both light­weight and qui­et.

Housing with integrated cooling
Hous­ing with in­te­grat­ed cool­ing—re­sem­bling the make­up of a bone. The cav­i­ties con­tain ad­di­tion­al hon­ey­comb struc­tures that chan­nel air di­rect­ly to the ar­eas that need to be cooled. The ad­van­tage is that the tubes con­ven­tion­al­ly used to sup­ply cool­ing air to the hous­ing are no longer re­quired.

Development by numerical simulation

Nu­mer­i­cal sim­u­la­tion be­gins with a hexa­he­dral mod­el, a fi­nite el­e­ment mod­el that is sub­ject­ed to spe­cif­ic loads and tem­per­a­tures. A com­put­er pro­gram then iden­ti­fies which of the hexa­he­drons are crit­i­cal for with­stand­ing the stress­es and which ones are not. The non-crit­i­cal ones are re­moved one by one un­til on­ly the es­sen­tial struc­tures re­main. Next, the com­put­er sim­u­lates dy­nam­ic stress­es and their im­pact over thou­sands of take­offs and land­ings. The mod­el ex­pos­es any weak points where the hexa­he­dral mesh needs to be mod­i­fied.

In the next step, the de­sign is op­ti­mized for ad­di­tive man­u­fac­tur­ing. Se­lec­tive laser melt­ing. In this process, thin lay­ers of the high-tem­per­a­ture iron-nick­el al­loy In­conel 718 are ap­plied to the sub­strate in pow­der form. A laser then melts the pow­der, fus­ing the lay­ers to­geth­er to cre­ate sol­id struc­tures. In prin­ci­ple, this method is suit­able for pro­duc­ing any geom­e­try, but it does re­quire any sup­port struc­tures and over­hangs to be re­moved or re­worked af­ter­wards. Op­ti­miz­ing the mod­el min­i­mizes the amount of work in­volved.

The CAD da­ta from the sim­u­la­tion can now be used for ad­di­tive man­u­fac­tur­ing with­out fur­ther pro­cess­ing. For qual­i­ty as­sur­ance pur­pos­es, MTU’s en­gi­neers de­vel­oped their own method for iden­ti­fy­ing any struc­tur­al weak points as ear­ly as pos­si­ble. Dur­ing the weld­ing process, a sen­sor records the time it takes for the pow­der melt­ed by the laser to reso­lid­i­fy and cool down. If this is un­usu­al­ly long, it’s a sign that the pow­der has not fused prop­er­ly with the lay­er be­low.

Pro­duc­tion of the blank for the brack­et takes on­ly a few hours. Be­fore the brack­et is mount­ed, it un­der­goes fur­ther qual­i­ty in­spec­tions to en­sure it is safe to use in the en­gine.

The new bion­ic brack­ets are now be­ing in­stalled in a test en­gine. Once they have passed en­durance test­ing and demon­strat­ed they meet the re­quire­ments for ap­proval, they can be rolled out in­to large-scale pro­duc­tion. “Then we’ll have an­oth­er im­por­tant mile­stone un­der our belt, paving the way for more de­vel­op­ments of this kind in the fu­ture,” Welling says. “Our plan is to pro­duce 15 to 30 per­cent of our en­gine com­po­nents us­ing ad­di­tive tech­nolo­gies by 2030. That’s no mean feat, and we know we’ve still got some chal­lenges to over­come. But we’re work­ing through them sys­tem­at­i­cal­ly to find so­lu­tions.”

There is a long list of com­po­nents that would be suit­able for ad­di­tive man­u­fac­tur­ing. Among the po­ten­tial can­di­dates are a hous­ing with in­te­grat­ed cool­ing, light­weight en­gine blades or a re­designed vari­able guide vane ac­tu­a­tor—a mech­a­nism cur­rent­ly made up of many small parts that have to be as­sem­bled man­u­al­ly.

“Ad­di­tive man­u­fac­tur­ing can al­so help achieve the tar­gets for re­duc­ing fu­el con­sump­tion and emis­sions in avi­a­tion,” Welling says. “Fol­low­ing na­ture’s ex­am­ple, we can make air­craft en­gines lighter, qui­eter and more ef­fi­cient.”

Bionic structures reduce weight
Additively manufactured brackets for oil lines weigh half as much as those made using conventional milling

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