Abstract

As a consequence of continued rising fuel prices and increased stringent engine emission regulations, it has become necessary to develop innovative, economical and environmentally friendly aero engines to ensure competitive advantage in the industry. Among them, counter-rotating open rotor(CROR) engine can greatly improve the propulsion efficiency by using the ultra-high bypass ratio because it does not require a nacelle and an appropriative reverse thrust device, and can further reduce fuel consumption and emissions compared with the conventional high bypass ratio turbofan engines. Therefore, it has received attention and become one of the development directions of future civil aviation engines. In order to evaluate the potential impact of an open rotor engine, it is necessary to develop an open rotor engine cycle modeling capability. To this end, this paper studies the modeling method of the open-rotor engine with the puller geared CROR as the object, and implements it in an in-house modular program of gas turbine performance prediction. In addition, the steady-state performance of the CROR is analyzed, and the model accuracy is verified based on the existing data. On this basis, the performance of the open rotor engine and the high bypass ratio turbofan engine is compared and results show that the counter-rotating open rotor engine has obvious fuel saving advantages.

The CROR model is developed on component level to provide flexible modeling capabilities for a series of engine cycles and internal engines performance data. Counter-rotating propeller (CRP) is one of the CROR specific component. The methodology used for counter-rotating propeller (CRP) modeling is similar to the one presented for single propellers, however some modifications are necessary. The calculation of the CRP starts from the aerodynamic performance of the single propeller and considers the interaction between propellers and the contraction of the air flow. It should be noted that the solution needs to be iterated due to the interaction of the front and rear propeller. For geared open rotor engine, a power transmission system is needed to transfer the power generated by power turbine to the CRP rather than a counter-rotating turbine for a direct drive open rotor engine. The transmission used for the CROR is a Differential Planetary Gearbox (DPG). Based on the above methodologies, component models of the CRP and DPG was developed in the in-house modular program. In addition, the characteristic maps corresponding to these components and the scaling techniques of the component characteristic maps have been developed. The main components in CROR include inlet, compressor (high /intermediate pressure compressor), combustor, turbines (high /intermediate turbine and power turbine), nozzle, CRP, PDG (Built into the CRP) and ducts. After determining the structure, an appropriate power management strategy is needed. This paper selects turbine entry temperature and rotational speed of both propellers as handles and creates the final mathematical model.

In order to examine the feasibility of the established CROR engine model, the model needs to be verified and compared. The CROR model was verified with data from another paper on the performance of open rotor engines and the calculation results show that the error between the two models is less than 1%.

The CROR model described above was selected to driving a single aisle transport aircraft which has a capacity to fly 5700 NM at cruise of M 0.785 carrying 160 passengers. Due to the similar technology assumptions and modeling process, a comparison can be made between the CROR and an advanced high bypass ratio turbofan which is derived from previous research projects. The comparison results show that the SFC of the open rotor engine is 15.67% lower than that of the turbofan engine. At other operating conditions, the fuel consumption of the CROR also has obvious advantages.