We continue on our journey through the IATA Technology Roadmap. With this story, we will cover the Zero Hub Fan. The Zero Hub Fan is one of the 14 new technology concepts IATA identified as coming into service in 2020 – 2035.
The Zero Hub Fan is indicated to Enter Into Service (EIS) in about 2020 and has a Technology Readiness Level of 7 (system prototype demonstration in a relevant environment).
The Zero Hub Fan (ZH fan) is expected to increase the mass flow rate at the fan inlet without increasing the case diameter. As a result of this design change, the fan’s total inner pressure ratio is increased. And the higher the pressure inside the gas turbine engine, the higher its efficiency. With that new paradigm also comes a requirement for new materials and related changes in manufacturing and deployment.
The concept of the Zero Hub Fan is diagrammed in Figure 1 below:
Figure 1 – Zero Hub Fan Concept
The ZH Fan is designed to pass the Hub-to-Tip ratio’s critical state. Many current gas turbine designs have a ratio of .29, with recent GT Engine improvements taking this ratio down to between .25 to .29. The Trent 1000 achieves a third state here with a Hub-to-Tip Ratio of <.25, which is the third stage outlined in the IHI Engineering Review, as noted in this article.
The Zero Hub Fan starts by reducing the hub diameter and, as a result, moves the blades closer to the centre of the hub. Nextly the blades are designed with wide leading edges to capture and process more air. These blades are highly complex in design, manufacture and application for several reasons. Figure 2 shows a Trent 1000 Gas Turbine engine with fully exposed blades, demonstrating their significant blade geometry.
Figure 2 Complexity of Geometry and Depth of Trent 1000 Blades
As these blades rotate, the tip (outer edge) moves faster than the hub. However, the blades’ angle of attack at the tip is lower than at the hub because it is moving at a much higher velocity than the hub. To make these blades more efficient, they have a twisted geometry. Rolls-Royce states that at takeoff, a Trent 1000 fan blade carries a load equivalent to the weight of 9 London buses.
The ZH Fan begins, as suggested earlier, with new materials. In the case of the Trent 1000, its blades are made of single crystal nickel-based superalloy to increase strength. These blades are further coated with advanced ceramic materials to insulate them from the extreme temperatures of the combustion process.
Blades are manufactured in a temperature-controlled vacuum furnace that allows the crystal to grow using controlled precision.
The Trent 1000 blade also contains complex air passages to cool the blade. Cooling holes are created by accurate laser drilling into the blade. This blade then lives in a high-pressure turbine where the gas temperature is 400 degrees higher than the blades’ alloy’s melting point; we note the previous emphasis on cooling and using passages through the blade.
More specifically, to the application of the ZH Fan, by capitalizing on the architecture and technologies of previous generations of Trent GT engines, the Trent 1000 has been designed and optimized to power the Boeing 787 Dreamliner family of aircraft. The Boeing 787 is the first application of the Trent 1000 Gas Turbine (GT) Engine, and the Trent 1000 is the first application of the ZH Fan!
Figure 3 Boeing 787 Dreamliner with the Trent 1000
The Trent 1000-powered Boeing 787 Dreamliner is 20% more efficient than the Boeing 767 aircraft that it replaces. Three-shaft architecture better supports “all-electric”(2) aircraft with a bleed-less engine system. The result of all of this is a more stable operating cycle.
The Trent 1000 also has several features to safeguard against core icing and a heated ESS (Engine Section Stator) system, which delivers advanced ice protection. (3)
As we began with this web story with the comment that the ZH Fan’s total inner pressure ratio is increased, we now note that the Trent 1000 is one of the first applications of this concept. This gas turbine engine has a bypass ratio of 10:1 and an overall pressure ratio of 50:1. This makes it the most advanced GT engine in service. The Trent 1000 also produces 62,264–81,028 lbf (of thrust).
- All-electric in this case, refers to the fact that these aircraft do not use hydraulics. Nowadays, electro-hydraulic actuators have replaced the centralized system with more localized systems that are controlled by electrical input, rather than mechanical linkages.