Performance of a gas turbine engine is monitored by computing a mass flow rate through the engine. Acoustic time-of-flight measurements are taken between acoustic transmitters and receivers in the flow path of the engine. The measurements are processed to determine average speeds of sound and gas flow velocities along those lines-of-sound. A volumetric flow rate in the flow path is computed using the gas flow velocities together with a representation of the flow path geometry. A gas density in the flow path is computed using the speeds of sound and a measured static pressure. The mass flow rate is calculated from the gas density and the volumetric flow rate.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 Temperature mapping portions of this invention were made with government support under contract DE-FC26-05NT42644 awarded by the U.S. Department of Energy. The government may have certain rights in the invention.