“…Hence, straight blades will also be assumed. Extension to account for compressibility and swept back blades is possible ( 6 , 10 ) and can be implemented in a future study.Figure 2Schematic description of the co-axial proprotor.…”
Section: 0 the Problem Description And Methodologymentioning
confidence: 99%
“…The torque balance of the co-axial proprotor can be achieved by changing the rear blade pitch angle as in this study, but also by changing the rotor’s rotational speed that is much easier to implement by electric motors commonly used in drones than by gas turbines used in larger aircraft. A summary of aerodynamic models used to analyse the co-axial proprotor during the decades after WWII is given in Playle et al ( 10 ) .…”
Low Reynolds number blade profiles of ReC=105–2×105 as based on the chord length and used for small unnamed air vehicles, and near space applications are investigated for single and counter-rotating (co-axial) proprotors, i.e. acting as rotors or propellers. Such profiles are prone for early stall, significantly reducing their maximum lift to drag ratio. Two profiles previously designed by our continuous surface curvature design approach named as CIRCLE are investigated in order to improve the performance of the proprotors. The profiles are redesigns of the common symmetric NACA0012 and asymmetric E387 profiles. Using general arguments based on composite efficiency and rotor’s lift to drag ratio, the performance envelope is noticeably increased when using the redesigned profiles for high angles of attack due to stall delay.A new approach is derived to account for the distance between the rotors of a co-axial proprotor. It is coupled with a blade element method and is verified against experimental results. Single and co-axial CIRCLE-based proprotors are investigated against the corresponding non-CIRCLE-based proprotors at hover and axial translation. Noticeable improvements are observed in thrust increase and power reduction at high angles of attack of the blade’s profiles, particularly for the co-axial configuration. Plots of thrust, torque, power, composite efficiency and aerodynamic efficiency distributions are given and analysed.
“…Hence, straight blades will also be assumed. Extension to account for compressibility and swept back blades is possible ( 6 , 10 ) and can be implemented in a future study.Figure 2Schematic description of the co-axial proprotor.…”
Section: 0 the Problem Description And Methodologymentioning
confidence: 99%
“…The torque balance of the co-axial proprotor can be achieved by changing the rear blade pitch angle as in this study, but also by changing the rotor’s rotational speed that is much easier to implement by electric motors commonly used in drones than by gas turbines used in larger aircraft. A summary of aerodynamic models used to analyse the co-axial proprotor during the decades after WWII is given in Playle et al ( 10 ) .…”
Low Reynolds number blade profiles of ReC=105–2×105 as based on the chord length and used for small unnamed air vehicles, and near space applications are investigated for single and counter-rotating (co-axial) proprotors, i.e. acting as rotors or propellers. Such profiles are prone for early stall, significantly reducing their maximum lift to drag ratio. Two profiles previously designed by our continuous surface curvature design approach named as CIRCLE are investigated in order to improve the performance of the proprotors. The profiles are redesigns of the common symmetric NACA0012 and asymmetric E387 profiles. Using general arguments based on composite efficiency and rotor’s lift to drag ratio, the performance envelope is noticeably increased when using the redesigned profiles for high angles of attack due to stall delay.A new approach is derived to account for the distance between the rotors of a co-axial proprotor. It is coupled with a blade element method and is verified against experimental results. Single and co-axial CIRCLE-based proprotors are investigated against the corresponding non-CIRCLE-based proprotors at hover and axial translation. Noticeable improvements are observed in thrust increase and power reduction at high angles of attack of the blade’s profiles, particularly for the co-axial configuration. Plots of thrust, torque, power, composite efficiency and aerodynamic efficiency distributions are given and analysed.
“…5, where axial and tangential induced components are shown). As the induced velocities are oscillating, their time-averaged magnitude is considered [39][40][41][42][43][44].…”
This paper provides design and performance data for two envisaged year-2050 engines: a geared high bypass turbofan for intercontinental missions and a contra-rotating pusher open rotor targeting short to medium range aircraft. It defines component performance and cycle parameters, general arrangements, sizes, and weights. Reduced thrust requirements reflect expected improvements in engine and airframe technologies. Advanced simulation platforms have been developed to model the engines and details of individual components. The engines are optimized and compared with “baseline” year-2000 turbofans and an anticipated year-2025 open rotor to quantify the relative fuel-burn benefits. A preliminary scaling with year-2050 “reference” engines, highlights tradeoffs between reduced specific fuel consumption (SFC) and increased engine weight and diameter. These parameters are converted into mission fuel burn variations using linear and nonlinear trade factors (NLTF). The final turbofan has an optimized design-point bypass ratio (BPR) of 16.8, and a maximum overall pressure ratio (OPR) of 75.4, for a 31.5% TOC thrust reduction and a 46% mission fuel burn reduction per passenger kilometer compared to the respective “baseline” engine–aircraft combination. The open rotor SFC is 9.5% less than the year-2025 open rotor and 39% less than the year-2000 turbofan, while the TOC thrust increases by 8% versus the 2025 open rotor, due to assumed increase in passenger capacity. Combined with airframe improvements, the final open rotor-powered aircraft has a 59% fuel-burn reduction per passenger kilometer relative to its baseline.
A primary design goal with a coaxial rotor is to minimize the combined sources of losses on the upper and lower rotors that have their source in aerodynamic interference. To this end, parametric studies were conducted using a free-vortex wake method to study the aerodynamic interference effects of changing interrotor spacing, blade twist rates, and blade planform on the interdependent loads produced on the upper and lower rotors, respectively. A formal, multistep optimization process was then conducted by coupling the aerodynamic method to an optimization approach based on the method of feasible directions, the goal being to expeditiously find the individual blade geometries that would give the highest levels of efficiency from the coaxial as a system. Because of the inherent aerodynamic differences between the upper and lower rotors of a coaxial, it is shown that the best performing coaxial rotors may require the use of different blade shapes on each rotor, but substantially different blade designs may also achieve similar values of aerodynamic efficiency. It is also shown that the nonconvexity of the design problem for a coaxial rotor may limit the usefulness of formal optimization methods, and extensive parametric studies may still be required in the process of design.
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