Profiled Annular Passageway for Gas Turbine Bifurcation Pressure Uniformity
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Solution Overview
Problem
The bifurcation in turbofan gas turbine engines causes significant peak-to-peak variation in the static pressure field, leading to undesirable forcing on fan blades and reduced aerodynamic efficiency, as the flow stagnates at the bifurcation leading edge and accelerates around it, resulting in high and low pressure areas.
Innovation Solution
A profiled annular fluid passageway is introduced upstream of the bifurcation, with varying radial thickness and curvature, to modify the flow and achieve a more uniform static pressure distribution from upstream of the bifurcation to downstream of the fan rotor, reducing the forcing on fan blades and improving aerodynamic efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the bifurcation is provided downstream of the OGVs to encase and direct electrical connections, then the electrical connections are protected and directed, but the bifurcation causes significant peak-to-peak variation in the static pressure field leading to undesirable forcing on fan blades
Solution Approach 1:
The profiled region is positioned upstream of the bifurcation to pre-condition the flow before it reaches the bifurcation. By modifying the flow characteristics in advance, the adverse pressure effects at the bifurcation are mitigated, reducing the peak-to-peak static pressure variation that causes fan blade forcing.
Solution Approach 2:
The profiled region has non-uniform radial thickness with a first circumferential portion having a smaller radial thickness than a second circumferential portion. This localized variation in geometry is specifically positioned to address the pressure distribution issues upstream of the bifurcation, creating a more uniform static pressure field in the critical region.
2Speed
If the flow is allowed to stagnate at the bifurcation leading edge, then the flow is directed around the bifurcation, but this creates high static pressure at the leading edge and low pressure in surrounding areas, causing significant pressure variation
Solution Approach 1:
The profiled region upstream of the bifurcation pre-modifies the flow to reduce the severity of stagnation effects. By adjusting the flow characteristics before they reach the bifurcation leading edge, the extreme pressure variations that would otherwise occur are attenuated.
Solution Approach 2:
The profiled region changes the geometric parameters of the flow passage, specifically the radial thickness varying circumferentially. This geometric parameter change modifies the flow parameters (velocity distribution, pressure distribution) to achieve a more uniform static pressure field upstream of the bifurcation.
3Stability of the object's composition
If outlet guide vanes are provided to straighten flow from the fan, then flow uniformity is improved, but the interaction with the downstream bifurcation still creates significant pressure variations that force fan blades
Solution Approach 1:
The profiled region is positioned to act on the flow before it reaches the bifurcation, pre-conditioning the flow to be more resistant to the adverse pressure effects of the bifurcation. This preliminary modification works in conjunction with the OGVs to maintain flow uniformity while reducing pressure variations.
Solution Approach 2:
The profiled region introduces localized geometric variations in the flow passage (different radial thicknesses in different circumferential portions) that specifically address the pressure distribution issues in the region upstream of the bifurcation, complementing the overall flow straightening function of the OGVs.
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 profiled region enhances the uniformity of the static pressure field, reducing fan blade vibration and improving aerodynamic performance by minimizing pressure variations and diffusion losses.
Implementation Method 1
The profiled region includes a first circumferential portion positioned adjacent a second circumferential portion. The first circumferential portion has a first average radial thickness and the second circumferential portion has a second average radial thickness. The first average radial thickness is smaller than the second average radial thickness. The profiled region of the passageway is configured to modify the flow through the passageway so as to improve the uniformity of a static pressure field
Data Source
AI summary
A gas turbine engine comprising in axial flow series: a fan having a fan rotor; a series passages defined between adjacent outlet guide vanes for guiding flow from the fan; and a bifurcation. The gas turbine engine further comprises a substantially annular fluid passageway extending from the fan to the bifurcation, the outlet guide vanes being positioned within the passageway. The passageway includes a profiled region. The profiled region includes a first circumferential portion positioned adjacent a second circumferential portion, the first circumferential portion having a first average radial thickness and a second circumferential portion having a second average radial thickness, the first average radial thickness being smaller than the second average radial thickness, wherein the first circumferential portion is positioned in a region corresponding to a circumferential position of the bifurcation, and wherein the profiled region is at an axial position corresponding to the axial position of the outlet guide vanes and the first circumferential portion extends continuously over two or more of the passages.