Challenges in Aero Engine Performance Modeling

As is the case with every machinery, manufacturers want to improve their products. This is especially true for aero engines, where even a small improvement in fuel consumption can lead to an advantage on the market. But with any type of propulsion equipment, regulations also play an important role, specifically that certain noise levels or CO¬¬2 emissions should not be exceeded. These factors combine to make the process of developing and manufacturing an aero engine anything but simple. In today’s blog, we’ll take a look at these challenges in more detail and briefly touch upon development strategies to account for such challenges.

PW 1000G
Figure 1: BERLIN – APRIL 26, 2018: The stand of MTU Aero Engines and high-bypass geared turbofan engine family Pratt & Whitney PW1000G. Exhibition ILA Berlin Air Show 2018.

In general, engineers have two options to develop a better engine. The first is to create a completely new design, like implementing a geared turbofan, which takes a lot of time and research. An example of this is the PW1000G engine from Pratt and Whitney, which was in development during the late 1990s and had its first flight test in 2008 [1]. This approach is less common which is reflected by other manufacturers who are backing down from the idea of using geared turbofans due to weight and reliability concerns [2]. The second option and this is the common method, is to gradually improve existing engines. This however brings new challenges, because simply improving one engine component does not necessarily mean that part of the machine will work well together with the rest of the machine. Furthermore, the design process for aero engines is very time-consuming. A general overview is shown in Figure 1. The process starts with an assumption for certain performance characteristics, for example, efficiencies for a compressor. After that, a cycle analysis is performed where the design point and off-design behavior are determined. With the newly gained information, the design process of the single component takes place. Upon successful creation of the component which satisfies all requirements, the process moves to the test phase. In this phase, the designed machine will be evaluated through experimental testing or intensive CFD studies. Modifications will be made if necessary to reach the desired operating conditions. Since changes were made to the geometry, these changes need to be investigated in an additional cycle analysis to understand how they will affect the overall engine performance. This process repeats until a converged solution is found.

Aero Engine Design Process
Figure 2: Aero engine design process

As one can imagine, the engine design and performance modeling process is a very time-consuming task, and the challenge is to find an appropriate balance between modeling accuracy and time. Therefore, it is very beneficial to improve the overall design process. One way to do this is to work with an initial geometry instead of empirical assumptions. The reason for that is that the efficiency of the preliminary design process, ergo the determination of a good initial design, is significantly higher compared to later stages of the design process. Figure 3 shows the relation between time spent and potential efficiency increase. 3D optimization is very time-intensive and if the design is found to be inadequate in this step, will result in the process starting all over. With this in mind, it is crucial to start with a well-suited geometry which reduces the risk of a complete restart.

Figure 3: Efficiency and time during different phase of the design process
Figure 3: Efficiency and time during different phases of the design process

The incorporation of an initial geometry into the cycle analysis allows us to work with more realistic parameter assumptions by simply using the geometry to determine these values. This enables us to move from the cycle analysis to the components optimization/testing with a very good initial geometry and shorten our process significantly.

To sum things up, the design process and modeling of aero engines is a very time-consuming task and stretches over several years. To improve the overall process, it is beneficial to start with a well-suited geometry. With this, we can run a more accurate representation of our cycle early on and spend less time in the 3D optimization step.

Axial Compressor Preliminary Design Generated in AxSTREAM
Figure 4:  Axial compressor preliminary design generated in AxSTREAM

Are you interested in enhancing the design process of aero engines? Reach out to us at or via our contact form and learn more about how we can help you achieve your goals faster by using AxSTREAM’s Generative Design Capabilities. Additionally. If you are an NPSS user, check out our latest webinar about the integration of AxSTREAM into NPSS to expedite the cycle analysis process.



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