Pressure- and Temperature-Sensitive Paint at 0.3-m Transonic Cryogenic Tunnel

Abstract Recently both Pressure- and Temperature-Sensitive Paint experiments were conducted at cryogenic conditions in the 0.3-m Transonic Cryogenic Tunnel at NASA Langley Research Center. This represented a re-introduction of the techniques to the facility after more than a decade, and provided a means to upgrade the measurements using newer technology as well as demonstrate that the techniques were still viable in the facility. Temperature-Sensitive Paint was employed on a laminar airfoil for transition detection and Pressure-Sensitive Paint was employed on a supercritical airfoil. This report will detail the techniques and their unique challenges that need to be overcome in cryogenic environments. In addition, several optimization strategies will also be discussed. 1. Introduction The accurate determination of spatially continuous pressure and temperature distributions on aerodynamic surfaces is critical for the understanding of complex flow mechanisms and for comparison with computational fluid dynamics (CFD) predictions. Conventional pressure measurements are based on pressure taps and electronically scanned pressure transducers or embedded pressure transducers, while temperature measurements are usually conducted using mounted devices such as thermocouples, RTDs, or thin film gauges. While these approaches provide accurate pressure and/or temperature information, they are limited to providing data at discrete points. Moreover, the integration of a sufficient number of these devices on a surface can be time and labor intensive and expensive. The Pressure-Sensitive Paint (PSP) and Temperature-Sensitive Paint (TSP) techniques allow for the accurate determination of pressure and temperature distributions over an aerodynamic surface and are based on an emitted optical signal from a luminescent coating. However, when full flight Reynolds number measurements are required, it is common to use a cryogenic facility, especially if an increase in model size is not a viable option. In this case, there are several challenges to overcome using both the PSP and TSP technique. This report will detail the results of both a TSP test and a PSP test at the 0.3-m Transonic Cryogenic Tunnel (0.3-m TCT) conducted at NASA Langley Research Center. These tests were aimed at re-introducing the techniques into the facility after more than a decade. In addition, several areas of improvement have been identified and will be discussed.