Specific Tasks at Virginia Tech Task 3 Interaction of a hot streak temperature gradient with the endwall

Preliminary experiments were conducted in which measurements of temperature, total pressure, and endwall adiabatic effectiveness levels were made with a flat temperature profile and coolant injection from an upstream film-cooled wall. This configuration along with the measurement locations are indicated in Figure 1. Note that these were preliminary measurements in which the experimental conditions, flow uniformity, and instrumentation were all checked in preparation for the final experiments in which coolant will be injected from a two-dimensional slot rather than the film-cooled wall.

Although it is not shown here, the experimental conditions for these tests consisted of a temperature difference between the film cooling and the mainstream of 28°C and the uniformity of the mainstream temperature was within 0.5°C. The thermal field temperatures were measured using a thermocouple rake while the total pressure measurements were made using a Kiel probe rake. The adiabatic effectiveness measurements were calculated based on the infrared camera measurements of the endwall temperatures as well as the coolant and freestream temperatures measured using thermocouples.

Figure 2 shows the non-dimensional temperature and pressure profiles upstream of the turbine vane measured at the locations indicated in Figure 1. As can be seen from these profiles there are large variations in both peak and profile shapes entering the turbine section. These variations are a result of the discrete film-cooling holes. Peak total pressure and minimum temperatures (maximum non-dimensional temperatures) coincide with the centerline of the film-cooling holes whereas between the holes, the values were much different. For example, consider the P1 measurement location which is mid-way between two cooling holes where the total pressure profiled is nearly flat but decreasing towards the wall. This total pressure profile is quite similar to what one would expect for an approaching turbulent boundary layer. For the P3 location, there is a peak total pressure at approximately 2% of the span which is much different than a turbulent boundary layer profile. Similar differences are indicated by the thermal field measurements.

Figure 3 shows preliminary adiabatic effectiveness measurements with 1% of the total cooling flow exiting the upstream rows of film-cooling holes. As can be seen, a 1% coolant injection from these film-cooling holes is not particularly effective in reducing the endwall temperatures in the turbine vane passage. Small fingers of coolant are indicated on the endwall, but for the most part the endwall effectiveness levels are near zero indicating no real cooling benefit. It is expected that the two-dimensional slot will provide better protection than the film-cooling injection since the coolant mix-out will be reduced.

0 0

Post a comment