Abstract
A gas turbine engine has supported the U.S. Military Academy’s mechanical engineering program for nearly three decades. Recent, substantial enhancements to the engine, controls, and data acquisition systems greatly increased the student experience by leveraging its broad capabilities beyond the original laboratory learning objectives. In this way, the laboratory served as a learning platform for more than just instruction on gas turbine fundamentals and the Brayton cycle.
The engine is a refurbished auxiliary power unit from Pratt & Whitney Aeropower, installed in the Embrauer 120 and similar to a unit installed on a U.S. Army helicopter. Whereas the original laboratory experience permitted students to test the engine at three different loads applied by a water brake dynamometer, the revised experience allowed for a broader range of test conditions. The original laboratory included single point measurements of three temperatures and two pressures, along with the fuel flow rate, dynamometer torque, and engine speed. The revised laboratory allowed the user to vary bleed air and engine loads across an operational envelope at a user-specified acquisition rate. The improved data acquisition system used LabVIEW™ and included multiple state sensors for pressure, temperature, fuel flow, bleed air, and dynamometer performance, thereby enabling a more complete analysis by accounting for the energy transported by bleed airflow and absorbed by the water brake. Students then quantified the uncertainty in their measurements and analysis. The new emphasis on uncertainty quantification, part of a program-level initiative, challenged students’ notion of “substitute and solve” while also familiarizing them with large, experimental data sets.
The re-envisioned laboratory raised the students’ level in the cognitive domain and served as their premier engine experience. Rather than merely observing engine adjustments across a small range of conditions, students designed their own laboratory experience. With the updated approach, students viewed a graphic of the turbine’s laboratory operating range and chose the key variables of interest — selecting data points within the laboratory operating range — and then justified their selections. The enhanced experience added analysis of flow exergy and exergetic efficiency. The exercise also challenged students to hypothesize why actual turbine performance was less than predicted and determine sources of error and uncertainty. Moreover, the new laboratory offers opportunities to expand the turbine engine’s utility from supporting a single thermal-fluids course to a multidisciplinary learning platform. Concluding remarks address concepts for augmenting course instruction in other courses within the curriculum, including heat transfer, mechanical vibrations, and dynamic modeling and controls.
An Applications Oriented Gas Turbine Laboratory Experience
