Total Temperature Measurements in Icing Cloud Flows Using a Rearward Facing Probe

Abstract

This paper reports on temperature and humidity measurements from a series of ice-crystal icing tunnel experiments conducted in June 2018 at the Propulsion Systems Laboratory at the NASA Glenn Research Center. The tests were fundamental in nature and were aimed at investigating the icing processes on a two-dimensional NACA0012 airfoil subjected to artificially generated icing clouds. Prior to the tests on the airfoil, a suite of instruments, including total temperature and humidity probes, were used to characterize the thermodynamic flow and icing cloud conditions of the facility. Two different total temperature probes were used in these tests which included a custom designed rearward facing probe and a commercial self-heating total temperature probe. The rearward facing probe, the main total temperature probe, is being designed to reduce and mitigate the contaminating effects of icing and ingestion of ice crystals and water droplets at the probe's inlet. The probe also serves as an air-sample inlet for a light absorption based humidity measurement. The paper includes a section which discusses total temperature and humidity measurement considerations, and another section which provides an analysis of the main probe's performance characteristics. A computational fluid dynamic model of the flow around the probe was also conducted to gain insight into the trajectory of the flow entering the probe inlet. The experiments included a series of tests in which the relative humidity of the facility flow was swept through with increasingly larger values. The data showed that the rearward facing probe can reasonably capture the flow's total temperature and humidity under mild to moderate icing conditions but can produce anomalous results under more intense icing conditions. The experimental data was also compared to an in-house developed thermodynamic model which takes into account the interaction of the main flow with the icing cloud. Comparison to the thermodynamic model showed that the rearward facing probe measured the predicted trends.

Ice-Crystal Icing Accretion Studies at the NASA Propulsion Systems Laboratory

“…The humidity was measured using a SpectraSensor instrument (Model WVSS-II) which uses an optical absorbance technique on the air drawn into the RFP. An accompanying paper [13] provides further details of the RFP used in the current tests.…”

“…Correspondingly, there is less evaporative cooling with increasing RH0,i resulting in smaller changes in total temperature at the exit (Te), as can also be seen shown on the right axis of Figure 7. An accompanying paper [13] provides further details on the reduction of data from the RFP.…”

“…The accretions at other flow conditions and AOAs are planned to be reported at a later date. However, some results from those conditions can be found in complementary papers presented in this conference which provide more details of instrumentation [13] or use the data for model comparison [14].…”

Analysis of Experimental Ice Accretion Data and Assessment of a Thermodynamic Model during Ice Crystal Icing

“…It should be noted that while the conditions upstream of the spray bar in the tunnel plenum were maintained constant, as it has been previously reported [2][3][4][5], conditions downstream at the test section change with the activation of the spray cloud. Modeling efforts [19][20][21][22][23] show that a thermodynamic interaction between the icing cloud and flowing air results in changes in total air temperature, , and humidity at the test section, compared with pre-spray conditions. In addition, changes occur in total water content, melt ratio and cloud particle size at the test section, compared with the initial spray conditions in the plenum.…”