Gas Turbine Fan Braking and Lubrication for Ground Windmilling
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Solution Overview
Problem
Gas turbine engines with geared architectures face challenges in preventing windmilling when stationary, leading to gear wear and requiring effective braking and lubrication systems to manage rotation and lubrication during ground conditions.
Innovation Solution
A braking system that selectively engages the fan with a disc brake and pawl mechanism to apply multiple levels of braking, and a lubrication system that pumps lubricant into the gearbox during windmilling, including a secondary pump for adequate lubrication, with sensors monitoring conditions for control unit intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a braking system is added to prevent windmilling, then gear wear is reduced, but device complexity increases
Solution Approach 1:
The braking system is segmented into two distinct components: a brake mechanism for controlled deceleration and a pawl mechanism for complete rotation prevention. This segmentation allows each component to be optimized for its specific function, with the brake handling gradual slowing and the pawl providing absolute locking, thereby reducing overall system complexity through functional decomposition
Solution Approach 2:
The brake is designed to engage first and slowly decelerate the fan before the pawl engages to completely prevent rotation. This preliminary action sequence prevents sudden mechanical shocks that would occur if the pawl engaged immediately at high rotation speeds, protecting the geared architecture from damage while maintaining system reliability
2Reliability
If a secondary lubrication pump is added for windmilling conditions, then gear lubrication is ensured, but device complexity increases
Solution Approach 1:
The lubrication system incorporates a dynamic control mechanism that automatically activates the secondary pump when rotation speed drops below 1000 rpm. This dynamic response ensures adequate lubrication is provided precisely when needed during windmilling conditions, while keeping the system simple by using automatic sensor-based control rather than complex manual or continuous control systems
Solution Approach 2:
The system uses a rotation speed sensor to automatically detect when windmilling conditions occur and triggers the secondary pump activation without external intervention. This self-service capability maintains reliable lubrication during low-speed operation while avoiding the need for additional complex control systems or manual operation
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 braking system effectively prevents windmilling and reduces gear wear, while the lubrication system ensures continuous lubrication, extending hardware life and maintaining engine efficiency during prolonged ground periods.
Implementation Method 1
The brake is configured to selectively engage the disc to apply the first level of braking to slow rotation of the fan
Implementation Method 2
The gearbox is supplied with a flow of lubricating fluid, which is typically oil, to protect the gears during operation
Data Source
AI summary
A gas turbine engine according to an exemplary aspect of the present disclosure includes, among other things, a fan and a braking system. The braking system is configured to selectively engage the fan during ground windmilling to apply a first level of braking to slow rotation of the fan. Further, when the rotation of the fan sufficiently slows, the braking system is further configured to apply a second level of braking more restrictive than the first level of braking.