Multi-disciplinary preliminary design assessments of pusher counter-rotating open rotors for civil aviation

摘要

As a consequence of fuel cost escalation and increased stringent engine emissionregulations, interest in counter-rotating open rotor engines (CRORs) has beenrenewed. R&D efforts are currently ongoing to develop the technologies required toensure the appropriate levels of structural integrity, noise, vibrations and reliability.The assessment of the impact of the main low pressure preliminary design and controlparameters of CRORs on mission fuel burn, certification noise and emissions isnecessary to identify optimum design regions. These assessments aid thedevelopment process when compromises need to be performed as a consequence ofdesign, operational or regulatory constraints. These assessments are not possible withthe state-of-the-art aero-engine preliminary design simulation tools.Novel 0-D performance models for counter-rotating propellers (CRPs) and differentialplanetary gearboxes, as well as 1-D and 0-D performance models for counter-rotatingturbines (CRTs) were developed and verified using available data. These models wereused to create 0-D pusher geared (GOR) and direct drive (DDOR) open rotor engineperformance simulation modules allowing the independent definition of the design andoperation of each of the two counter-rotating parts of the CRP and CRT.A multi-disciplinary preliminary design simulation framework was built using the novelengine performance modules together with dedicated CROR aircraft performance,engine geometry and weight, gaseous emissions and certification noise simulationmodules. Design space exploration and trade-off studies were performed and minimumfuel burn design regions were identified for both the pusher GOR and DDOR. A 160PAX aircraft flying a business mission of 500 NM was chosen for these studies.Based on the assumptions made, the main conclusions of these studies are as follows.· Fuel burn reductions of ~1-2% are possible through optimised propeller control· The propeller diameter for minimum mission fuel burn lies between 4.26 and 4.7 m· The design nozzle pressure ratio for minimum mission fuel burn lies between 1.55and 1.6· CRPs with 13 or 14 blades per propeller provide minimum mission fuel burn· Increasing spacing between the propellers reduces noise significantly (~6 EPNdB foreach certification point) with a relatively small fuel burn penalty (~0.3-0.5%)· Relative to unclipped designs, 20% clipped CRPs reduce flyover noise by at least 2.5EPNdB and approach noise by at least 4.5 EPNdB. The corresponding fuel burnpenalty is ~2 % for a GOR and ~3.5% for a DDOR.· Sideline and flyover noise can be reduced by increasing the diameter of the CRP andappropriately controlling CRP rotational speeds. Approach noise can be reduced byeither reducing the diameters or the rotational speeds of the propellers.· The rotational speed of the forward propeller for minimum noise is higher than that forminimum mission fuel burn for all the studied CROR designs.· Regardless of clipping, reducing the rotational speed of the rear propeller relative tothe forward propeller reduces noise and, to a certain limit, also mission fuel burn.(further reductions in rotational speed would have an adverse effect on fuel burn)· An increase in the number of blades results in an increase in certification noise.The main recommendations for further work are as follows.· Integrating the 1-D CRT model with the 0-D DDOR performance model in order toassess the impact of different CRT design criteria at engine and mission levels· Developing preliminary design methods to account for changes in aircraft weight andaerodynamics due to changes in engine design and required cabin noise treatment.