Engineers consider a variety of factors when designing jet engine test cell instrumentation systems, including engine control, safety and performance.
The typical cycle deck is a computational model of a gas turbine engine used to determine expected performance at different stages within the engine.
Test Cell Support
- Applications of Cycle Deck Models for Test Cell Performance Evaluation and Engine Simulation
- Engine Performance Analysis
- Jet Propulsion System Support
U.S. Air Force jet engine testing uses actual engines to verify/correlate engine test cells prior to and during field installation. Engine performance calculation and acceptance are based on sensor measurements corrected to "standard day" readings. The typical cycle deck is a computational model of a gas turbine engine used to determine expected performance at different stages within the engine. A high-fidelity, dynamic engine signal simulator based on cycle deck models could significantly reduce the cost of test cell health verification and test system checkout.
Using Engine Simulators
The typical cycle deck is a computational model of a gas turbine engine used to determine expected performance at different stages within the engine. Click image for larger view.
To accomplish this, the effectiveness of an engine simulator in reducing or replacing the use of live engine runs needed to be determined, including a method for simulating mechanical transitions between engine states, an alternative for characterization of test cell air flow, and an approach for mapping outputs of the cycle deck model to real-world test cell sensors. The algorithms based on the cycle deck model for use as real-time sensor validation routines in existing and new jet engine test systems needed to be developed.
First, a cycle-deck-based engine simulator was developed. It was then evaluated as a verification and correlation tool, by comparing the simulation data with test cell data and assessing the simulator at a test site. This was used to construct a new approach to sensor validation using a top-level design diagram of the cycle-deck-based engine simulator. A generic framework was developed that can be used on related projects in the future.
The generic framework includes two operating modes:
- Cycle Deck - Use real-world data to calculate values for parameters at different engine stages
- Intermediate and Depot - Convert cycle deck parameters into recognizable test cell parameters
There are several requirements of the sensors. First, they must be individually configurable, meaning that each sensor can be software- or hardware-controlled separately. For the software-controlled sensors, the operator sets the sensor values. Sensors which are linked to hardware have each input to the simulator linked to a test cell sensor input; each output is able to generate a scaled voltage.
Data Comparison and Analysis
Data from 31 depot-tested engines was compared to cycle deck performance with the same input conditions to determine the consistency of the cycle deck using actual test cell data. Evaluation revealed cycle deck engine performance within 1.5% of depot-tested engines and within 3.8% of intermediate level-tested engines.
The relationship between the performance of the cycle deck and an actual T56 engine was identified. Analysis showed the cycle deck to be equivalent to an engine with 107.98% efficiency. This observation is supported by the upper limit of 108% imposed on measured test cell performance.
Data was analyzed for T56 test cell facility modifiers and F110/F101 engine test cells using the standard deviation to determine the limit of the simulator’s test cell correlation and verification capability. The simulator shows excellent performance for outdoor testing of the T56 engine with no test cell-induced effects on air flow. For depots, facility modifiers can be added to the cycle deck through a SwRI-developed GUI.
Sensor validation algorithms were developed based on the cycle deck. Using an iterative process, the algorithms calculate modeled engine output based on input sensor data, and then compare the result with the measured output. If the observed data does not fit the model, the algorithm adjusts one sensor at a time to determine the likely cause for the discrepancy. Using these routines, the observed torque of 150+ engine runs was compared with the torque output from the sensor routines using the same input sensor values. Observed torque exceeded modeled torque at several points which have a calculated efficiency at or near the specified maximum limit, indicating potential sensor measurement errors in the original data.
Currently, most sensor validation is performed during post-data analysis. These algorithms can be embedded in test system software and run in the background to perform sensor validation in real time on the target test system and sensors.
Test cell correlation analysis software measures engine efficiency and plots correlation correction paths.
SwRI is working on a new method to correlate test cells using an engine cycle model when a test cell undergoes a significant modification of the physical structure or the instrumentation system hardware or software.
Southwest Research Institute (SwRI) has performed engine performance analysis test cell data to independently verify and validate the algorithms used in the test cell. SwRI has also developed improved algorithms that reduce the noise in the data and improve the usability of the data.
Test cell data has been analyzed in combination with failure data to determine patters that indicate future failures, so that some failures can be detected before they cause catastrophic engine damage and the engine can be appropriately maintained.
From jet propulsion requirements and facility design, to systems and software development, SwRI provides experienced and timely jet propulsion systems solutions. For nearly 20 years, SwRI has provided jet engine propulsion services and advice on test and repair facilities to the U.S. Air Force, Army and original equipment manufacturers (OEM). SwRI is a recognized leader in developing innovative solutions and providing independent engineering assessments, including:
- Engine test cell instrumentation
- Test cell facilities and equipment
- Engine test software
- Calibration and certification of test cells
- Engine trending and diagnostics (ET&D)
- Engine trending and analysis training development and delivery
- Engine component test stations
SwRI’s success in engine and engine component testing is based on a multidisciplinary systems engineering approach to problem solving. Comprehensive expertise in design, modeling, fabrication and integration enables SwRI to address client needs. SwRI has implemented an ISO 9001:2000 compliant program for all design and manufacturing processes, including engineering analysis tasks and software development efforts.
Test Cell Components
SwRI engineers designed and fabricated a unique dynamometer test stand configured to accept and measure 250 ft.-lb. to 25,000 ft.-lb. of torque and 80,000 lbs. of thrust at speeds up to 200 rpm.
SwRI engineers have developed plant layouts and design detail options for an engine test facility to evaluate large engine-generator sets fabricated by the client. Exhaust emissions, acoustic noise and ground-borne vibrations from the engine generators were key topics of consideration.
Implementation of the automated and semi-automated control of a jet engine test evolved from operational and performance tests included in technical manuals. SwRI is adept at developing test software from requirements to acceptance testing and post-delivery software maintenance.
Test Cell Support
Using instrumentation error analysis over normal ambient conditions of the test cell and coordination with engine manufacturers, SwRI instrumentation engineers develop technical data to calibrate intermediate and depot jet engine test cells. Software engineers implement semi-automated calibration software and are knowledgeable in error calculations such as SAE ARP4990 for calculating fuel flow in turbine flowmeters. SwRI also coordinates calibration requirements with various calibration organizations, such as the Air Force Precision Measurement Equipment Laboratory (PMEL), Air Force Metrology and Calibration (AFMETCAL) program and the on-site quality team, including development of Calibration Measurement Requirements Summary (CMRS) documents.
Design considerations for engine throttle controls include redundancy and safety, operator ease of use, alignment, computer interface, and application given the cost drivers. Local closed-loop control of stepper motors are used to achieve ±0.25 degree power lever angle repeatable commandable set points. Ramp rates and safety cutback and shutdown commands also are featured.
Test Cell Instrumentation Design
When designing a test cell instrumentation system, SwRI engineers consider control of the engine; measurement of safety, performance and facility parameters; and performance calculations. Safety shutdown and redundant safety parameters, such as engine speeds, engine temperature and fuel flow, provide a safety net to the operator. Engineers also interface with engine buses (such as MIL-STD-1553B) for parameter acquisition and take into account measurement characteristics such as linearity, temperature sensitivity, hysteresis, resolution, shielding and grounds, and National Fire Protection Agency (NFPA) regulations. Design encompasses selection of sensors, data acquisition, data processing, data display/recording equipment, and special interfaces and cabling.
Test Cell Correlation/Certification
SwRI engineers have more than 20 years of experience in performing jet engine test cell correlation, which is required to ensure standardization of all testing facilities that certify serviceable status of the same Type/Model/Series (TMS) turbofan, turboshaft and turbojet engines. The typical reference base is an engine, provided by the OEM, that is baselined for all gas path parameters to meet specification requirements. Running the calibrator, data collection, data analysis and (as required) correction back to baseline is mandated because each facility is unique. SwRI is working on a new method to correlate test cells using an engine cycle model when a test cell undergoes a significant modification of the physical structure or the instrumentation system hardware or software.
aircraft engine performance • cycle deck models • test cell support • test cell performance • engine simulator • sensor validation • engine performance analysis • jet propulsion system