Non-Parallel Shaft Gas Turbine APU Design
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Solution Overview
Problem
Aircraft auxiliary power units (APUs) often operate below their maximum power capacity, leading to inefficiencies in space utilization and manufacturing complexity, as their sizing is typically determined by peak generator power and environmental control system requirements, resulting in suboptimal use of available space and increased costs.
Innovation Solution
The design incorporates a serial flow communication system with a turbine, engine compressor, and gear train, featuring non-parallel shafts and a differential gear train with bevel gears, allowing for efficient power distribution to both compressors and generators, reducing the overall length and pressure drop within the APU while enabling modular assembly and maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the APU is sized for maximum generator power and ECS flow requirements, then the power capacity is sufficient for peak demands, but the APU operates below maximum power at other operating points leading to inefficiencies
Solution Approach 1:
The patent implements a variable geometry inlet guide vane system that dynamically adjusts the airflow angle and quantity to the compressor based on operating conditions. This allows the APU to maintain optimal compressor inlet conditions across a range of power outputs, enabling efficient operation at partial load while maintaining the power capacity needed for peak demands. The dynamic adjustment of guide vane angles optimizes the matching between turbine power output and compressor power requirements at each operating point.
2Device complexity
If the APU components are arranged in a conventional parallel configuration, then the layout is simple, but the space utilization is inefficient and the overall length is increased
Solution Approach 1:
The patent transitions from a conventional parallel shaft configuration to a series shaft arrangement where the compressor shaft and turbine shaft are aligned in series rather than parallel. This dimensional reorganization allows the exhaust gases to flow directly through the turbine and out the rear of the APU, eliminating the need for complex flow reversal sections and reducing the overall length. The series configuration optimizes space utilization by arranging components along the gas flow path rather than requiring lateral expansion.
Solution Approach 2:
The patent nests the generator within the compressor housing, with the generator rotor positioned inside the compressor assembly. This nested arrangement allows the generator to share space with the compressor components, reducing the overall volume required for the APU while maintaining both functions. The generator is integrated into the existing structural envelope rather than requiring separate dedicated space.
3Ease of operation
If the shafts are arranged parallel to the engine axis, then the alignment is straightforward, but the pressure drop increases and airflow efficiency decreases
Solution Approach 1:
The patent orients the compressor shaft and turbine shaft in series along the gas flow direction rather than parallel to the engine axis. This reorientation aligns the shafts with the natural flow path of the exhaust gases, allowing smooth flow from the combustor through the turbine and out the rear. This configuration minimizes flow separation and reduces pressure drop while maintaining straightforward alignment through the series arrangement.
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
This configuration enhances the operating efficiency and stability of the APU, reduces space requirements, and simplifies assembly and maintenance by allowing components to be positioned non-parallel to the engine axis, thereby improving airflow and reducing pressure drops, leading to a more compact and efficient power unit.
Implementation Method 1
generating exhaust gases in a combustor of a gas turbine engine to drive a turbine about an engine axis
Implementation Method 2
a first shaft operatively connecting the turbine to the engine compressor via a gear train and a third shaft connected to the turbine; and the second shaft is operatively connected to the turbine via the gear train
Data Source
AI summary
An auxiliary power unit (APU) includes, in serial flow communication: an engine compressor, a combustor and a turbine, the turbine rotatable about an engine axis. A first shaft operatively connects the turbine to the engine compressor and extends non-parallel to the engine axis. A second shaft operatively connects the turbine to a load and extends non-parallel to the engine axis. A method of operating an APU is also described.