Propfan Engine Contoured Outer Casing Design
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Solution Overview
Problem
Conventional propfan engines face limitations in cruise speed due to drag rise at higher speeds, primarily caused by the structural robustness requirements of propeller blade roots, leading to increased noise, aerodynamic losses, and mechanical excitation, as well as inefficiencies in rotor performance due to supersonic airflow and large nacelle diameters.
Innovation Solution
A propfan engine design featuring a contoured outer casing with a gradually increasing and then decreasing diameter along the flow direction, incorporating diffusive and blockage sections to reduce flow velocities and Mach numbers, thereby alleviating root choke concerns and enhancing rotor efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the propeller blade roots are made thick to ensure structural robustness, then the structural strength is improved, but the drag rise and noise increase at high speeds
Solution Approach 1:
The patent applies parameter changes by carefully controlling the blade root thickness parameter. The blade roots are made sufficiently thick to ensure structural robustness under high aerodynamic and mechanical loads, but not excessively thick to avoid increased drag and noise. This optimization of the thickness parameter resolves the contradiction between strength and harmful factors.
2Reliability
If the nacelle diameter is increased to diffuse flow upstream of the propeller stage, then the hub Mach number is reduced and rotor efficiency is improved, but large free-stream over-speed occurs over the outer span of the propeller blades
Solution Approach 1:
The patent applies local quality by creating different flow conditions at different radial positions. The nacelle is designed with a specific diameter that provides flow diffusion and reduced hub Mach number in the inner region (improving rotor efficiency), while avoiding excessive free-stream over-speed at the outer blade span. This localized optimization of flow conditions resolves the contradiction.
3Speed
If the propeller gas turbine engine operates at transonic cruise speed, then the cruise speed is increased, but the airflow between blade roots becomes supersonic causing increased noise and aerodynamic losses
Solution Approach 1:
The patent applies parameter changes by optimizing the blade root geometry parameters to control the airflow velocity between blade roots. The blade roots are designed with specific thickness and spacing parameters that prevent the airflow from becoming supersonic even at transonic cruise speeds, thereby reducing noise and aerodynamic losses while maintaining high cruise speed capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design reduces aerodynamic losses, noise, and mechanical excitation, allowing for improved rotor efficiency and increased cruise speed capabilities while minimizing nacelle diameter increases, resulting in better performance and reduced specific fuel consumption.
Implementation Method 1
incorporating diffusive and blockage sections to reduce flow velocities and Mach numbers
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
The present disclosure relates to a propfan engine (100) comprising: one or more rotor stages (110, 120) comprising a plurality of rotors; and an outer wall (130) comprising an outer profile (132), at least a portion of the outer profile defining a substantially circular cross-section, wherein the diameter of the substantially circular cross-section increases in the direction of flow over the outer wall and downstream of a leading edge (112, 122) of the rotors, and the diameter increases at substantially all points defining the circumference of the substantially circular cross-section. The present disclosure further relates to propfan engine (100) comprising: one or more rotor stages (110, 120) comprising a plurality of rotors; and an outer wall (130) comprising an outer profile (132), the outer profile defining a cross-section, wherein the cross-section of the outer profile comprises a maximum diameter (134, 136) at a point upstream of a leading edge (112, 122) of the rotors, the diameter reducing between the maximum diameter and the leading edge of the rotors, and wherein the outer profile comprises a point of inflection (135, 137) between the maximum diameter and the leading edge of the rotors.