DEVELOPMENT OF THE PERSPECTIVE HIGH-BYPASS FAN BLADE

ABSTRACT

The paper provides a detailed overview of various design solutions of advanced engine technologies aimed at increasing performance, reducing noise and increasing efficiency. Key features include the use of wide-chord and long fan blades without vibration-absorbing mid-span shrouds. To solve the problem of high-intensity noise, the peripheral speed of the fans was reduced. Modern high-load single-stage supersonic flow fans have demonstrated the ability to improve efficiency and reduce fuel consumption. In addition, the concept of increasing gas temperature in turbojet engines to maximize thrust while minimizing weight and drag is being explored. In general, advances in engine design, such as twin spool and triple spool gas turbine engines with increased gas temperatures and bypass ratios, highlight the potential for performance improvements in future engine technologies.

АННОТАЦИЯ

В статье представлен подробный обзор различных конструктивных решений перспективных технологий двигателей, направленных на повышение производительности, снижение шума и повышение эффективности. К ключевым особенностям относится использование широкохордных и длинных лопастей вентилятора без антивибрационных полок. Для решения проблемы высокоинтенсивного шума была уменьшена окружная скорость вентиляторов. Современные высоконагруженные одноступенчатые сверхзвуковые вентиляторы продемонстрировали возможность повышения эффективности и снижения расхода топлива. Кроме того, изучается концепция повышения температуры газа в турбореактивных двигателях для максимизации тяги при минимизации веса и лобового сопротивления. В целом, достижения в конструкции двигателей, такие как двухвальные и трехвальные газотурбинные двигатели с повышенной температурой газа и степенью двухконтурности, подчеркивают потенциал улучшения производительности в будущих технологиях двигателей.

Keywords: fan blade, jet engine design, propulsive efficiency, innovations

Ключевые слова: лопатка вентилятора, проектирование турбореактивного двигателя, эффективность движителя, конструкция, инновации.

Introduction

In recent years, the fan blade has undergone a number of design changes that have led to increased efficiency, durability, and other general characteristics. Among these changes can be noted the use of the latest materials and manufacturing technologies. Fan blades are made from high-strength and lightweight materials such as titanium and composite materials. The choice of such materials is determined by such requirements as strength, durability and resistance to high temperatures and loads.

Article [8, p. 4] reviews the progress made in the design and analysis of fan blades used in commercial jet engines, as well as design methods and selection of modern materials such as titanium (Ti-6Al-4V alloys), metal matrix composite, hybrid - metallic materials to achieve better efficiency.

Advanced manufacturing technologies such as additive manufacturing or 3D printing are used to create complex blade designs with high precision and stability.

The efficiency and performance of a gas turbine engine largely depend on the design and functionality of the fan blades. The improvement of the new promising high-performance blade is achieved by changing the aerodynamic shape. To ensure maximum efficiency and performance, the aerodynamic shape of the blades is optimized using computational fluid dynamics (CFD)[2, p. 14; 9, p. 3]. The blades must be designed to effectively draw in air and compress it before entering the combustion chamber.

High bypass ratio gas turbine engine fan blades must be resistant to foreign object damage (FOD). If debris, sand, stones, or birds enter the engine, the fan blades may be damaged. To reduce this risk, new fan blades have protective coatings or features that can withstand the elements without compromising performance.

Advanced technologies improve maintainability and thereby reduce maintenance costs. Digital monitoring and predictive maintenance technologies track their performance and identify potential problems before they cause costly failures.

Design features of an aero engine fan blade

The development of a promising engine is characterized by such determining factors as flight safety, comfort, minimal impact on the environment, as well as economic factors: reduction of operating costs, production costs, etc.

The design of modern high-load single-stage fans with supersonic flow around the blades (π_f = 1.67) at EGT (Exhaust Gas Temperature) = 1600 K and bypass ratio = 9 makes it possible to increase the overall pressure ratio =30 and reduce the specific fuel consumption at takeoff mode while reducing the specific weight.

With a further increase in the bypass ratio, the specific gravity will increase, which in turn is undesirable. A modern solution to promising engines is a propfan engine, in which the propeller is a small-sized, highly loaded variable-pitch propeller. While maintaining efficiency, reducing the diameter by 40%, you can achieve higher flight speeds (up to 850 km/h). Due to the high cycle parameters and high flight speed, the specific fuel consumption of such engines will be lower compared to a gas turbine engine of the classical design.

Another approach is significantly increase the gas temperature in front of the turbine of a turbojet engine in order to obtain the maximum possible thrust with minimal weight and aerodynamic drag of the power plant.

The technical proposal for this issue is the use of an afterburner, thanks to which it was possible to increase the starting thrust. However, this type of design led to a heavier structure and a decrease in fuel efficiency.

As a result of a number of studies, the design solution of the new generation engine is two-shaft, three-shaft turbofan engines with increased gas temperature (EGT = 1700-1800 K) and bypass ratio= 8-11, single-stage supersonic fan with pressure ratio of the fan π_fb = 1.6-1.8, and peripheral speed on the outer diameter U = 450-500 m/s.

The fan blades of the promising engine are shroudless wide-chord, relatively long blades.

The anti-vibration mid-span shroud is designed to limit the amplitude of alternating stresses in the rotor blades and has positive and negative sides. An anti-vibration mid-span shroud is usually used when choosing a blade with a large aspect ratio. In this case, the mid-span shroud can be considered as an additional support for the beam. Another advantage of such a shroud is to prevent the destruction of the entire blade as a whole, since when a bird hits a large mass, and more often when the blade is destroyed, the above-shroud part comes off. An increase in hydraulic losses and a decrease in stage efficiency by 3-4%, an increase in the labor intensity of manufacturing and the weight of the blade constitute the negative side of this design.

Thus, the abandonment of anti-vibration mid-span shroud will lead to a significant reduction in hydraulic losses.

Vibrations, in turn, will be damped by honeycomb fillers, which will be located in the internal cavities of a hollow wide-chord blade, which will lead to sufficient rigidity.

One of the important problems when designing a fan is the appearance of high-intensity noise. By reducing the peripheral speed of the fan to 250 m/s and using a moderate degree of pressure increase, it is assumed that noise reduction can be realized.

Another design solution to the noise problem is the use of a three-circuit engine with rotating fan blades, where work is redistributed between the circuits by changing the air flow through the intermediate circuit using flaps to optimize operating speeds.

Comparative analysis of prototypes

Important for ensuring the successful design and production of aircraft engine fan blades is the improvement of the use of the latest technologies tested on already known engines, as well as the improvement of the latter. In turn, close collaboration between aerodynamicists, engineers, manufacturing and quality specialists leads to the creation of a turbofan fan that meets the stringent requirements of modern aircraft propulsion systems.

An example of such cooperation is the LEAP (Leading Edge Aviation Propulsion) engine, a high bypass ratio turbofan engine developed by CFM International, a joint venture between General Electric (USA) and Safran Aircraft Engines (Snecma, France).

The LEAP engine's fan blades feature an advanced 3D aerodynamic design designed to maximize efficiency, reduce fuel consumption and minimize environmental impact. Compared to today's best CFM56, this turbofan engine will consume 16% less fuel and emit 16% less carbon dioxide (CO2) emissions, as well as lower fan noise levels[14].

The latest composite technology RTM (resin transfer molding) was used for the first time in the market of narrow-body aircraft, according to CFM, on the LEAP fan. This technology makes it possible to create a more complex blade shape, reduce the number of blades to 18, and greatly minimize the weight of the fan[14].

Developed by Rolls-Royce, the Trent 1000 three-shaft engine is an example of high efficiency, reliability and performance. Recognized as one of the quietest engines in service today, its fan has the highest bypass ratio of any Trent engine.

Trent 1000 TEN (Thrust, Efficiency and New technology) – being the latest modification, it demonstrates greater traction and better fuel consumption, which are achieved by using the latest technologies. Tests aimed at improving fuel efficiency are being studied closely by Rolls-Royce and have already been used on the Trent XWB[15].

To improve the environmental performance of the engine, the new development of the promising Ultra Fan is expected to use the ALECSys system (Advanced Low Emissions Combustion System). The development of ALECSys is supported by the European Union's Clean Skies initiative, as well as by the UK Aerospace Technology Institute and Innovate UK[16].

The most technologically advanced commercial turbofan engine over the past 25 years is the GE90 engine, developed by a competitor of the previous company and at the same time one of the leaders in the global aircraft engine industry, General Electric.

Among the advantages of the iconic jet engine, recognized throughout the world, are record thrust, low noise levels, minimization of emissions and fuel consumption. To reduce weight and thermal conductivity, the fan blades are made using a large amount of pre-laid, hand-laid carbon fiber reinforced plastic (CFRP) fabrics.

The weight of the GE90 turbofan fan without supporting stages is 15.6% of the total mass, while its cost is 14.5%.

Based on the GE90, the GEnx fan features 18 composite blades with a bypass ratio of 9. The overall pressure ratio of this engine is 58, and fuel efficiency is increased by 15% compared to the CF6[17].

The innovative GEnx turbofan engine produces 90% more thrust and is 15% more economical and at the same time more reliable than existing designs. The remaining 10% of engine thrust is provided by combustion jets from the internal engine duct.

Engine reliability is enhanced by the use of a large amount of lightweight composite sound insulation, which is necessary to achieve low noise levels.

The fan blade is made of carbon fiber, which significantly reduces the overall weight of the engine.

Thanks to the special configuration of the blades, it was possible to reduce their number and at the same time increase the efficiency of the fan.

One of the latest modifications, GEnx-2B, was introduced in the fall of 2019, developed for the 747-8. The fan of such an engine is lighter in weight and more resistant to corrosion.

The company's largest engine to date is the GE9X, which features fan blades made from fourth-generation carbon fiber composites, making them stronger, lighter, thinner and more efficient. The trailing edge of the blade is made of a special fiberglass composite that absorbs shock loads away from it. Additionally, the GE9X is 10% more fuel efficient than the GE90.

The company's largest engine, the GE9X, is equipped with the smallest number of blades - 16.

As a comparison, Graph 1 shows the trend in fan diameters of advanced engines.

Figure 1. Trend in diameters (mm) of turbofan engines

Conclusion

In conclusion, significant advances have been made in the design of modern high-load single-stage fans and advanced motors in increasing efficiency, reducing fuel consumption and minimizing noise levels [1, 3, 4, 7].

Strictly speaking, the new advanced gas turbine fan blades include advanced design features such as aerodynamic geometry, advanced materials, resistance to destructive corrosion and ease of maintenance, which improve the efficiency, durability and overall performance of the gas turbine engine. These design features are necessary to meet the growing demands of the aerospace industry for increased efficiency, reliability and sustainability [5, 12].

When designing an engine with a high bypass ratio, as a result of limiting the rotation speed, an increase in the diameter of the fan and the number of stages of its turbine is observed. As a result, the weight and dimensions of the engine also increase. Accordingly, it is necessary to search for new design solutions taking into account weight minimization using CFD methods [2, 9, 11, 13].

By introducing innovative technologies such as wide chord and honeycomb blades, turbofan engines and higher gas temperatures, engineers are pushing the boundaries of aircraft engine design. These developments offer the potential for improved performance, increased thrust and overall efficiency in future aerospace applications. Continued research and development in this area continues to drive progress and innovation in aviation technology.

References:

1. Alan H. Epstein. Aeropropulsion for Commercial Aviation in the Twenty-First Century and Research Directions Needed. 2014 https://doi.org/10.2514/1.J052713
2. Clint J. Knape. Aerodynamics of Fan Blade Blending. Wright State University. 2019
3. Christopher Hughes, Dale Van Zante, James Heidmann. Aircraft Engine Technology for Green Aviation to Reduce Fuel Burn, 2012 https://doi.org/10.2514/6.2011-3531
4. Elena de la Rosa Blanco, Cesare Hall, D. Crichton. Challenges in the Silent Aircraft Engine Design. 2012 https://doi.org/10.2514/6.2007-454
5. G.A. Fitzpatrick, F.D/ Lloyd “Establishing Best practice in the Design and Manufacture of Hollow Titanium Fan Blades”. RTO AVT Workshop on “Intelligent Processing of High Performance Materials”, Brussel, Belgium, 13-14 May 1998
6. A.John, N. Qin. Understanding Fan Blade Tip Aerodynamics - University of Sheffield S. Shahpar - Rolls-Royce Proceedings of 12th European Conference on Turbomachinery Fluid dynamics & Thermodynamics. 2017; Stockholm, Sweden
7. Károly Beneda, Bence Sipula. Design of An Ultra-High Bypass Ratio Fan Stage For A Research Turbojet Engine. 2019, Hungary
8. Leye M. Amoo. On the design and structural analysis of jet engine fan blade structures Progress in Aerospace Sciences 60 (2013) 1–11
9. Riccardo Balin. Modern Advances in Fan and Compressor Design Using CFD. 2015
10. Rula M. Coroneos, Rama Subba, Reddy Gorla. Structural Analysis and Optimization of a Composite Fan Blade for Future Aircraft Engine. 2012
11. Sebastian Spinner, Dennis Keller, Rainer Schnell, Marco Trost. A Blade Element Theory Based Actuator Disk Methodology for Modeling of Fan Engines in RANS Simulations. AIAA 2020-2749 2020 https://doi.org/10.2514/6.2020-2749
12. Takehiro Okura. Materials for Aircraft Engines. ASEN 5063 Aircraft Propulsion Final Report 2015
13. Xiangyang Deng, Fushui Guo, Yesheng Liu, Pinlian Han. Aero-Mechanical Optimization Design of a Transonic Fan Blade. 2013 https://doi.org/10.1115/GT2013-95357
14. AEC to showcase LEAP engine composite components at Farnborough 2012 (reinforcedplastics.com)
15. https://naukatehnika.com/dvigatel-trent-ot-rolls-royce.html?ysclid=ltbjblvfww255196841naukatehnika.com
16. An exciting new chapter for the Trent 1000 | Rolls-Royce
17. GEnx Engine | GE Aerospace