Flexible Non-Intrusive Heat Flux Instrumentation for the AFRL Research Turbine

Abstract

This paper describes a large scale heat flux instrumentation effort for the AFRL HIT Research Turbine. The work provides a unique amount of high frequency instrumentation to acquire fast response unsteady heat flux in a fully rotational, cooled turbine rig along with unsteady pressure data to investigate thermal loading and unsteady aerodynamic airfoil interactions. Over 1200 dynamic sensors are installed on the 1 & 1/2 stage turbine rig. Airfoils include 658 double-sided thin film gauges for heat flux, 289 fast-response Kulite pressure sensors for unsteady aerodynamic measurements, and over 40 thermocouples. An overview of the instrumentation is given with in-depth focus on the non-commercial thin film heat transfer sensors designed and produced in the Heat Flux Instrumentation Laboratory at WPAFB. The paper further describes the necessary upgrade of data acquisition systems and signal conditioning electronics to handle the increased channel requirements of the HIT Research Turbine. More modern, reliable, and efficient data processing and analysis code provides better handling of large data sets and allows easy integration with the turbine design and analysis system under development at AFRL. Example data from cooled transient blowdown tests in the TRF are included along with measurement uncertainty.

Comparison of Thin Film Heat Flux Gauge Technologies Emphasizing Continuous-Duration Operation

“…After each thermal property was individually characterized, the thermal product ρc p k was examined. Table 4 compares the present study with measurements at two temperatures to previously published data from AFRL [27], Oxford [23,24], MIT [3], and VKI [32] as well as manufacturer-reported specifications [45][46][47]. Although this table shows a wide range of values, this spread is not unexpected.…”

“…To create these sensors, the manual application of platinum paint may be used, but lithography processes can significantly improve the control of dimensionality and alignment for double-sided gauges. A lithography technique typically requires advanced equipment but has been used to successfully execute gauge designs using nickel- [3,26] and platinum- [5,27,28] resistive elements.…”

Development of coated heat flux gauges for fast responding measurements

“…The current through the surface heater creates voltage modulations at the same frequency as illustrated in figure 7(b). The heat flux dissipated on the surface (q 0 ) can then be calculated though equation (7):…”

“…Figure 11 also displays the linear line with a k s /d s = 3842 (Wm −2 K −1 ), as determined in the previous section. The values of q 0 plotted on the ordinate represent the calculated heat flux based upon equation (7) with corrections for mean heat flux lost to the surrounding environment. The uncertainty bounds plotted in figure 11 account for the uncertainty of the temperature calibrations, heater currents, and voltage acquisition, leading to an estimated overall uncertainty of 8% for mean heat flux.…”

“…Sensors of this type have been used for decades in turbomachinery applications. Traditionally, HFGs have been used in short-duration facilities with typical test durations on the order of seconds [7][8][9][10]. As these sensors transition from shortduration environments to more engine-representative testbeds, additional protections must be deployed to ensure the survivability of the gauges [11].…”