Booster Compressor Speed via Epicyclic Gear Unit
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Solution Overview
Problem
Current turbo machine designs face challenges in achieving high bypass ratios and pressure ratios while minimizing engine weight and drag, particularly due to conflicting optimum design parameters for the fan and core engine, which result in increased torque loads and larger engine sizes.
Innovation Solution
A fan and booster compressor system utilizing an epicyclic gear unit that drives the booster compressor at a rotational speed function of both the fan and high pressure compressor speeds, allowing for a smaller booster compressor diameter and reduced torque load on the low pressure shaft, with the booster compressor rotating faster than the fan over a range of rotational speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the bypass ratio is increased to improve fuel efficiency, then the fan pressure ratio becomes relatively low, but this results in lower rotational speed and higher fan shaft torque
Solution Approach 1:
An epicyclic gear unit is introduced as an intermediary mechanism between the fan shaft and booster compressor. This gear unit transmits and transforms rotational motion, allowing the booster compressor to rotate at a different speed than the fan while maintaining proper aerodynamic matching, thereby resolving the torque-speed conflict caused by high bypass ratios
Solution Approach 2:
The system changes the rotational speed parameter of the booster compressor relative to the fan through the epicyclic gear mechanism. By varying the gear ratio, the booster can operate at optimal speeds independent of fan speed, enabling high bypass ratios without excessive torque loads on the fan shaft
2Stress or pressure
If booster stages are coupled to the fan shaft to achieve desired pressure ratio, then the booster rotates more slowly, but this requires more stages or increased radius which affects fan hub line and increases fan tip diameter
Solution Approach 1:
The epicyclic gear unit acts as a speed transformation intermediary, decoupling the rotational speeds of the fan and booster compressor. This allows the booster to achieve higher rotational speeds without increasing fan tip diameter, while still delivering the required pressure ratio with fewer stages or smaller radius
Solution Approach 2:
The gear unit pre-adjusts the rotational speed of the booster compressor before it enters the compression stages, ensuring optimal blade speeds are achieved from the outset. This prevents the need for increased fan hub line or tip diameter that would otherwise be required to compensate for slow rotation
3Reliability
If a geared fan arrangement is used to reduce low pressure turbine weight and aerodynamic loading, then higher bypass ratios are achieved, but the gearbox adds considerable weight and cost
Solution Approach 1:
The patent extracts the gear mechanism from the traditional geared fan configuration and repositions it to drive only the booster compressor rather than the entire fan assembly. This selective application reduces the size and weight of the required gearbox while still achieving the beneficial effects of speed differentiation for improved turbine performance
4Volume of moving object
If the booster compressor diameter is reduced to minimize engine size and weight, then fewer stages are required, but this may compromise aerodynamic performance
Solution Approach 1:
The epicyclic gear unit changes the rotational speed parameter of the booster compressor, allowing smaller diameter compressors to achieve the same blade tip speeds and aerodynamic performance. This enables reduced engine size and weight while maintaining compression efficiency through optimized speed-diameter relationships
Data Source
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AI summary
In a gas turbine engine, the booster compressor is driven by both the low pressure or fan shaft and high pressure shaft through a differential gear arrangement. The rotational speed of the booster compressor is intermediate between the speed of the fan and the speed of the high pressure compressor.