High-tech guessing game: Behind all the cables, hoses and sup­port­ing struc­tures, it’s hard to make out the latest off­spring of the partner­ship between MTU Aero Engines and Pratt & Whitney. The core module of the next gen­era­tion in the geared turbofan family is being tested on a rig at the German engine-maker’s Munich location. Some 1,300 meas­ure­ment points have been wired up on the high-pressure compressor to record the widest possible number of parameters. Such rig tests involve a lot of time and effort, but the engineers consider them indis­pensable and even plan to test two dif­ferent engine components this year—with the support of the aero­nautics research program funded by the German Federal Ministry for Economic Affairs and Energy. “Rig tests are an essential element in our tech­nol­ogy process. We use them to verify the per­for­mance of inno­vative products under the relevant operating conditions. This helps us pre­pare the way for the next wave of new technologies,” says Dr. Stefan Weber, Senior Vice President Technology and Engineering Advanced Programs at MTU. It is part of the company’s research policy to carry out such tests on its two key products, the compressor and the low-pressure turbine, at four-to-five-year intervals.

In this particular case, the focus lies on enhancements to the PW1100G-JM Geared Turbofan^TM. To maintain the technological lead established by the Airbus A320neo engine, which only recently entered service, efforts must be made to further reduce its fuel consumption. This will be achieved by improving the performance of the high-pressure compressor, developed in collaboration with Pratt & Whitney, and that of MTU’s high-speed low-pressure turbine. This is not an easy task, given that both components already have an extremely high degree of fuel conversion efficiency. “We will have to work hard on a number of issues that, in the end, will enable the progress needed,” says Dr. Gerhard Kahl, project manager in charge of compressor rig 268. Because the compressor components have to match the dimensions of the original engine, the number of stages has not been increased. Attention has therefore been focused on optimizing the blade profile and reducing parasitic losses. In engineering parlance, parasitic losses are unwanted phenomena that interrupt the flow of air, such as leakages or gaps be­tween rotating and static parts. In their search for potential improvements, the engineers make use of increasingly sophisticated design tools. But the joint MTU and Pratt & Whitney development team also has to make sure that this doesn’t affect the compressor’s operating stability. For this reason, the rig tests not only include analyzing aerodynamic factors but also record data concerning tem­pera­ture, gap widths, vi­bra­tions and many other parameters.

When the compressor is mounted on the test rig, it is powered by an array of electric motors with a combined output of 16 mega­watts—the equiva­lent of 18 Formula One racing cars. After passing through the com­pres­sor, the air is throt­tled down to at­mos­pheric pressure and evacu­ated via an exhaust chamber. “MTU has ac­cu­mu­lated many decades of ex­peri­ence in engine assembly and testing. This gives us a head start in our cur­rent ac­tiv­ities,” says Kahl. By the end of the year, the ex­haus­tive com­pres­sor testing schedule will have racked up 140 hours.

The rig testing is already finished for en­hance­ments to the low-pressure turbine origi­nally de­vel­oped for the geared turbo­fan under the sole re­spon­sibil­ity of MTU. These tests, total­ing 100 hours, were car­ried out on the high-altitude test rig at the University of Stuttgart, where MTU tra­di­tion­ally tests its turbines. In this case too, the de­si­gners verified the ef­fi­ca­cy of the im­prove­ments to the engine’s aero­dynamic per­for­mance. “Without changing the di­men­si­ons, we re­designed the blades and further reduced the aero­dynamic losses oc­curring in the peripheral areas of the turbine,” says Dr. Irene Raab, project manager in charge of turbine rig 456. A detailed analy­sis of the results is now in progress. The next stage, sched­uled for next year, in­volves testing the complete second-generation geared turbofan. After that, the even more fuel-efficient GTF will be re­quired to undergo the usual cer­ti­fi­ca­tion procedures, some of which will probably be carried out in Munich. And that’s not all: Like their col­leagues in the compressor department, the turbine team also has de­vel­oped more inno­vations than can be im­ple­mented under the present program. They could also benefit future engine generations.