aviation

Low-pressure turbines: The path to world-class manu­facturer

A journey that dates back 45 years: MTU is now a world-class manu­facturer of low-pres­sure turbines—and its high-speed, high-end version for the Geared Turbofan™ is unmatched.

04.2019 | Text: Denis Dilba

Text:
Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.

Kopf

What was MTU’s first step on the path to be­com­ing a lead­ing man­u­fac­tur­er of low-pres­sure tur­bines? Sur­pris­ing­ly, it was the de­vel­op­ment of an ex­haust cas­ing. Ex­act­ly how this hap­pened is some­thing Lud­wig Schweikl knows first­hand, be­cause he and his col­leagues were the ones who built it. “At that time, the ear­ly 1970s, cor­po­rate man­age­ment made a strate­gic de­ci­sion to get in­to the com­mer­cial en­gine busi­ness,” says Schweikl, who had a long tenure as head of de­sign at MTU. The ex­perts al­ready had ex­pe­ri­ence with mil­i­tary en­gines and had de­vel­oped and built the in­ter­me­di­ate-pres­sure tur­bine for the RB199, the en­gine for the Tor­na­do. Over the course of this pro­duc­tion process, MTU came in­to con­tact with Amer­i­can en­gine man­u­fac­tur­er Pratt & Whit­ney. “Some­how this led to an in­vi­ta­tion for the MTU de­vel­op­ment de­part­ment to vis­it the Pratt head­quar­ters in East Hart­ford,” the en­gi­neer re­calls. It would be a great way to get to know one an­oth­er, said the Amer­i­cans. Sounds good, re­spond­ed the Ger­mans. So, Schweikl soon found him­self on a plane mak­ing its way to the US and was thus the first MTU de­vel­op­er to meet his coun­ter­parts at Pratt & Whit­ney.

AEROREPORT series: 50 years of innovation at MTU

“They were very skep­ti­cal as to whether or not we had any­thing to of­fer. At that time, Pratt & Whit­ney was the world’s lead­ing en­gine man­u­fac­tur­er and MTU was just a small com­pa­ny,” the 82-year-old says. But he made a good im­pres­sion, and MTU was asked to try its hand at the ex­haust cas­ing for a new ver­sion of what was then the clas­sic medi­um-haul JT8-D. The col­lab­o­ra­tion worked smooth­ly, far ex­ceed­ing Pratt & Whit­ney’s ex­pec­ta­tions. MTU’s skilled en­gi­neers im­pressed the Amer­i­can en­gine man­u­fac­tur­er—which then asked them to de­vel­op the low-pres­sure tur­bine for the JT10-D: a larg­er, more pow­er­ful fol­low-up to the JT8-D. It was an hon­or and an or­der that Schweikl and his de­vel­op­er team grate­ful­ly re­ceived. “This marked the be­gin­ning of the low-pres­sure tur­bine busi­ness for MTU,” Schweikl says. Thus be­gan a true de­vel­op­ment race, with one in­no­va­tion top­ping the oth­er—a race that con­tin­ues to this day.

aeroreport_1_pw2000

The low-pressure turbine for the PW2000 was the first to incorporate a solution for cooling the casing, called the active clearance control (ACC) system.

aeroreport_2_v2500_iae

This development led to a significant increase in the efficiency of the low-pressure turbine for the V2500, which powers the A320 family and others.

aeroreport_3_gp7000

Assembly of the low-pressure turbine for the GP7000.

aeroreport_4_pw1100g

The high-speed low-pressure turbine for the Pratt & Whitney Geared Turbofan™ family is appreciably quieter than conventional models.

aeroreport_5_pw1000g_v2500_ndt

The low-pressure turbines for the PW1000G and V2500 in comparison.

aeroreport_6_a320neo

More fuel efficient, cleaner and quieter—the Airbus A320neo.

Ex­perts share the word about MTU’s com­pe­tence

The first low-pres­sure tur­bine for the JT10-D, soon re­named the PW2000, made a shin­ing im­pres­sion thanks to a spe­cial tech­ni­cal re­fine­ment. As the amount of thrust changes, ro­tors and en­gine cas­ings ex­pand and con­tract at dif­fer­ent speeds. This can lead to greater clear­ances and in turn to per­for­mance loss­es. To com­bat this prob­lem, the en­gine in­cor­po­rat­ed the first so­lu­tion for cool­ing the cas­ing, called the ac­tive clear­ance con­trol (ACC) sys­tem. This off­set the dif­fer­ence in the ther­mal ex­pan­sion of the com­po­nents, thus re­duc­ing clear­ance and con­sid­er­ably im­prov­ing the ef­fi­cien­cy of the en­tire as­sem­bly. Pratt & Whit­ney con­tributed the idea and the patent, while MTU made it a re­al­i­ty. “To­day it is stan­dard in every en­gine,” says Schweikl.

Word about MTU’s ex­per­tise in low-pres­sure tur­bines spread through­out avi­a­tion cir­cles. As a re­sult, a short time lat­er Schweikl and his team al­so took on the de­vel­op­ment of the low-pres­sure tur­bines for the V2500 pro­gram. A low-pres­sure tur­bine has a ma­jor in­flu­ence on an en­gine’s over­all per­for­mance. With the V2500, which pow­ers the A320 fam­i­ly and has be­come one of the most im­por­tant pro­grams in MTU’s com­mer­cial port­fo­lio, the en­gi­neers sys­tem­at­i­cal­ly ap­plied what they learned with the PW2000. This meant they could sig­nif­i­cant­ly im­prove the ef­fi­cien­cy of the low-pres­sure tur­bine for the V2500.

Just three stages in the high-speed low-pres­sure tur­bine

Many more MTU low-pres­sure tur­bines fol­lowed: they are found in busi­ness jet en­gines, in the pow­er tur­bines of tur­boshaft en­gines for heavy-lift he­li­copters, in tur­bo­fan en­gines for medi­um- and long-haul air­lin­ers, and even in the GP7000 for the Air­bus A380 mega­lin­er. MTU has num­bered among the glob­al elite in low-pres­sure tur­bine tech­nol­o­gy for a long time now. The Mu­nich com­pa­ny’s cur­rent mas­ter­piece is the high-speed low-pres­sure tur­bine for the Geared Tur­bo­fan™ (GTF): op­ti­miz­ing the aero­dy­nam­ics down to the small­est de­tail has achieved a high­er de­gree of ef­fi­cien­cy. At the same time, the high ro­ta­tion­al speeds that re­sult from the GTF’s re­duc­tion gear­box mean the stages work hard­er. That’s why the pres­sure tur­bine mod­ule in the A320neo en­gine needs just three stages. As a re­sult, space, weight, main­te­nance costs, not to men­tion fu­el con­sump­tion and there­fore CO2 emis­sions all de­crease.

And as if this weren’t im­pres­sive enough, the new tur­bine is al­so much qui­eter than con­ven­tion­al mod­els. Its noise emis­sions are at high­er fre­quen­cies that are bet­ter ab­sorbed by the at­mos­phere, to the point where the hu­man ear can bare­ly de­tect them. With this world-class low-pres­sure tur­bine, a key com­po­nent with­out which the GTF would not ex­ist, MTU to­day has moved in­to a league of its own. But even this ex­cep­tion­al tur­bine has room for im­prove­ment, through new ma­te­ri­als, pow­er­ful com­put­er sim­u­la­tions, and new­ly op­ti­mized aero­dy­nam­ics. MTU en­gi­neers are cur­rent­ly work­ing at it—and in do­ing so, they will write the next chap­ter in the ex­tra­or­di­nary sto­ry of the low-pres­sure tur­bine’s de­vel­op­ment.

You may also be interested in these articles:


AEROREPORT is an aviation magazine published by MTU Aero Engines, Germany's leading engine manufacturer. Neatly summed up, AEROREPORT offers an MTU perspective on the world of aviation. The word “REPORT” in the title stands for the high-tech and outstanding service “made by MTU”. “AERO” represents broader horizons and general aviation topics.

Flying and the technologies that make it possible yield a wealth of content for the magazine, which makes for some truly fascinating reading: stories from over one hundred years of history and plenty of exciting features on topics with a bearing on the future of aviation, such as climate change, population growth and limited resources.