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

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

02.2019 | Text: Monika Weiner

Text:
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.

aeroreport_natur-als-vorbild

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.

aeroreport_natur-als-vorbild_2

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

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