Hybrid Electric Active Clearance Control for Turbine Acceleration
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Solution Overview
Problem
Gas turbine engines face challenges in maintaining optimal clearance between rotor blades and case structures during rapid acceleration, as rotor stages expand more quickly than their surrounding case structure, leading to inefficiencies and potential limiting conditions.
Innovation Solution
A hybrid electric propulsion (HEP) system that integrates an active clearance control (ACC) system, where the system determines a power allocation between the gas turbine engine and the electric motor based on available electric power, and adjusts the target clearance using the ACC system to maintain efficient operation during acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the gas turbine engine accelerates rapidly, then the acceleration rate increases, but the rotor stages expand more quickly than the case structure causing clearance issues
Solution Approach 1:
The patent applies dynamics by making the clearance control system adaptive and variable rather than fixed. The ACC system dynamically adjusts cooling fluid flow to the case structure based on real-time operating conditions, allowing the clearance to be actively managed during rapid acceleration. This dynamic control enables the system to maintain reliable clearance despite the rotor stages expanding faster than the case structure would naturally accommodate.
Solution Approach 2:
The patent changes the thermal parameters of the case structure by controlling the temperature of cooling fluid directed at it. By adjusting the cooling fluid flow rate and temperature, the system modifies the thermal expansion characteristics of the case structure, allowing it to expand at a controlled rate that matches or exceeds the rotor stage expansion during rapid acceleration, thereby maintaining acceptable clearance.
2Loss of energy
If the clearance between blade tips and case structure is reduced, then efficiency improves, but the risk of contact and damage increases during thermal expansion
Solution Approach 1:
The ACC system employs feedback control by continuously monitoring engine operating parameters such as temperature, pressure, and rotational speed. Based on this feedback, the controller adjusts the cooling fluid flow to the case structure in real-time, dynamically maintaining the optimal clearance. This feedback mechanism allows the system to keep the clearance small for efficiency while automatically preventing it from becoming too small during rapid thermal expansion, thus avoiding blade contact.
Solution Approach 2:
The system performs preliminary action by pre-cooling or pre-heating the case structure in anticipation of upcoming thermal changes. During predicted rapid acceleration or thrust increases, the ACC system adjusts cooling fluid flow in advance to prepare the case structure for thermal expansion, ensuring clearance is maintained before critical conditions arise. This proactive control prevents clearance issues before they occur rather than reacting after problems develop.
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 integration of the HEP system with the ACC system allows for efficient power allocation and clearance control, enabling the gas turbine engine to maintain optimal efficiency and prevent limiting conditions during rapid acceleration.
Implementation Method 1
Rotor stages (including blades, disks, and cases) are known to radially expand due to centrifugal force and thermal expansion (e.g., due to engine operating temperatures). Active clearance control (ACC) systems have been developed to selectively direct cooling fluid at the case structure to more closely control the clearance between blade tips and clearance structure.
Implementation Method 2
an electric motor configured to assist the gas turbine engine by rotating a first shaft of the gas turbine engine
Data Source
AI summary
A method is provided for an HEP system that includes a gas turbine engine and an electric motor configured to assist the gas turbine engine by rotating a first shaft of the gas turbine engine. The method includes receiving a throttle command, and determining, based on an amount of electric power available to the electric motor, a power allocation between the gas turbine engine and the electric motor for an acceleration period during which a rotational speed of the first shaft is accelerated to implement the throttle command. The method also includes determining a target clearance between a tip of a rotor blade and a case structure for the acceleration period and, during the acceleration period, implementing the power allocation and operating an active clearance control (ACC) system to establish the target clearance. A system for an aircraft and a method for a HEP system are also disclosed.