Compressor Exit Pressure Monitoring for Rotating Stall Detection
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Solution Overview
Problem
Current gas turbine engine start sequences rely on conservative thresholds for shaft speed and turbine gas temperature to prevent rotating stall, leading to increased starting times and potential failed start attempts, as monitoring turbine gas temperature is a crude method for ensuring sufficient ventilation and rotor bow clearance.
Innovation Solution
A method that predicts compressor exit pressure fluctuations using a variable dependent on both current and lagged compressor exit pressure, with a first-order recursive filter to smooth readings and an integrator counter for consistent prediction, ensuring accurate clearance of rotating stall before initiating combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conservative thresholds for shaft speed and turbine gas temperature are used to prevent rotating stall, then reliability of start sequence is improved, but starting time increases
Solution Approach 1:
The patent changes the monitoring parameter from turbine gas temperature to compressor exit pressure fluctuation. By detecting pressure fluctuations at the compressor exit, the system can more accurately determine when rotating stall has cleared, allowing for optimized threshold settings that reduce starting time while maintaining start reliability.
Solution Approach 2:
The patent replaces the thermal monitoring approach (turbine gas temperature) with a pressure-based monitoring approach (compressor exit pressure fluctuation). This substitution provides more direct and timely information about rotating stall clearance, enabling faster and more reliable start sequence decisions.
2Reliability
If turbine gas temperature monitoring is used to guard against insufficient ventilation, then reliability is improved, but measurement precision is insufficient
Solution Approach 1:
The patent substitutes temperature monitoring with pressure fluctuation monitoring. Compressor exit pressure directly reflects the aerodynamic conditions in the compressor, providing precise detection of rotating stall clearance. Pressure fluctuations are a more direct indicator of stall conditions than temperature, which is a crude indirect measure.
Solution Approach 2:
The patent uses compressor exit pressure as an intermediary parameter that directly reflects rotating stall conditions. By monitoring pressure fluctuations at the compressor exit, the system obtains a precise intermediate measurement that accurately indicates when rotating stall has cleared, enabling better control decisions.
3Reliability
If threshold values are set conservatively to ensure sufficient flow, then reliability is improved, but productivity decreases
Solution Approach 1:
The patent changes the control parameter from temperature-based thresholds to pressure-fluctuation-based thresholds. This enables more accurate determination of rotating stall clearance, allowing for less conservative threshold settings that increase the engine start rate while maintaining reliability through precise pressure monitoring.
Data Source
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AI summary
A method of predicting the condition of a compressor with respect to rotating stall is disclosed. The method comprises the steps of: i) comparing the difference between the largest and smallest values of a variable occurring during a time period with a difference threshold, the variable at any given time being dependent on the compressor exit pressure at that time, and ii) predicting either that the compressor is in rotating stall or that the compressor is not in rotating stall in dependence upon the result of the comparison.