The axial flow turbofan HP compressor and turbine were, and continue to be, a battle between size, efficiency, and power. These two components affect the overall performance of the engine. While the design is still an on-going challenge, I can see the fun parts coming. Materials and elegantly designed component modules are things I love to think about. In the mean time the battle continues.
Figure 1: HP Compressor and Turbine Concept rendering (Solid Edge ST9 and KeyShot 6)
The HP Compressor and Turbine
The high pressure (HP) compressor and turbine are a matched pair, joined by a shaft. The compressor forces the mass of air into the combustor. After it has been ignited, that mass of air is expelled through the turbine. The turbine then extracts the power from the heated air sufficient to power the compressor. Any energy remaining in the heated air can then be converted into thrust or other needs.
The HP compressor and turbine have been roughed out for a little while now. Early on it became evident that the design of the pair would be pinned between two difficult limits, namely a large, high-performance bearing, and a bypass duct. After mocking up the cad models in Fusion 360 and Solid Edge, we’ve learned even more about the problems we face. Some things you just have to visualize.
We passed the original compressor design through computational fluid dynamics software (CFD) to compare the modeled result to the expectations from the ideal 2D mathematical model. The results compared very well, and subsequently we have moved forward. Since then, the pair have been redesigned twice so that they fit the needs of the project.
Figure 2: Early HP Compressor model static pressure rise in cascade validated in Autodesk CFD 2017
We have made great jumps in understanding much of the compressor research through the 20th century. A myriad of well known mathematical fluids and thermodynamics principles have been poured through. However, the real struggle has been to get a grip on 8 decades of research into the realistic behavior of fluids in turbojet cascades, diffusers, and combustors. Pioneers like Carter, McKenzie, Howell, Lieblein, Soderberg, Horlock, and so many others come to mind. The turbomachinery industry relies on their published results, which are coefficient defined in a narrow range of observed situations. At every iteration we have to verify that the design remains within well researched limits before reviewing the results.
We have also had some significant setbacks. We work around them, we learn, we move forward. This is all part of the frustrating process. I will bring out more details and topics relating to the project as we progress. I hope this will lead to some great discussions on this site with folks throughout the respective industries.
Boyce, Meherwan P. Gas Turbine Engineering Handbook. 4th ed., Elsevier, Inc., 2002.
Cumpsty, Nicholas. Jet Propulsion, a Simple Guide to the Aerodynamic and Thermodynamic Design and Performance of Jet Engines. 2nd ed., Cambridge University Press, 2003.
Dixon, S L, and C A. Hall. Fluid Mechanics and Thermodynamics of Turbomachinery. 2nd, 6th, and 7th ed., Butterworth-Heinemann/Elsevier, 2010.
Falck, Niclas. “Axial Flow Compressor Mean Line Design.” MA Thesis, Lund University, 2008.
Mattingly, Jack D. Elements of Propulsion: Gas Turbines and Rockets. 2nd ed., AIAA Education Series, American Institute of Aeronautics and Astronautics, Inc., 2006.
Mattingly, Jack D, William H. Heiser, and Daniel H. Daley. Aircraft Engine Design. American Institute of Aeronautics and Astronautics, 1987.