The widespread use of the gas turbine as a means of aircraft propulsion engine or for electrical power production has provided a considerable momentum for improving its efficiency. However without a greater understanding of the unsteady flowfield, in particular the flow mechanisms that cause losses, it is difficult to further improve efficiency.

Since entropy is the only means of quantifying aerothermal losses, a fast response entropy probe has been developed and built. The entropy cannot be measured directly, but only inferred from other measured flow properties such as the total temperature and the total pressure. Therefore the principal components of the miniature (diameter 1.8mm) fast-response entropy probe (FENT) are a fast response aerodynamic probe and an unsteady total temperature probe based on the thin film technology, see Fig.1. The thin film gages are fabricated by sputtering 200nm thick nickel in a serpentine shaped onto a 1.8mm semi-cylindrical quartz substrate. This design provides high spatial resolution, high temperature sensitivity, and robustness, which ensure that the unsteady total temperature measurement capability is in the same range as that of the unsteady total pressure (40kHz).

As an example, Fig. 2 shows the measured time-resolved entropy distribution measured at the rotor exit of the axial turbine LISA.