The measurement of wind tunnel flow quality at transonic speeds

The measurement of wind tunnel flow quality for the transonic flow regime has been plagued by the inability to interpret complex unsteady flow field information obtained in the free stream. Traditionally hot wire anemometry and fluctuating pressure techniques have been used to quantify the unsteady characteristics of a wind tunnel. This research focuses on the application of these devices to the transonic flow regime. Utilizing hot wire anemometry, one can decompose the unsteady flow field with a three sensor technique, to obtain fluctuations associated with the velocity, density, and total temperature. Implementing thermodynamic and kinematic equations, new methods for expanding the measured velocity, density, and total temperature fluctuations to obtain additional fluctuations are investigated. The derived static pressure fluctuations are compared to the static pressure fluctuations obtained with a conventional fluctuating static pressure probe. The results of this comparison are good, which implies that the individual velocity, density, and total temperature components are time accurate. In the process of obtaining a high quality fluctuating flow field information, it was necessary to evaluate the calibration of the hot wire sensors. A direct calibration approach was compared to a conventional non-dimensional technique. These two calibration techniques should have resulted in the same hot wire sensitivities. There were significant differences in the hot wire sensitivities as obtained from the two approaches. The direct approach was determined to have less errors due to the added heat transfer information required of the indirect approach. Both calibration techniques demonstrated that the velocity and density sensitivities were in general not equal. This suggests that the velocity and density information cannot be combined to form a mass flow. A comparison of several hot wire techniques was included to highlight the errors obtained when assuming that these sensitivities are the same. An evaluation of the free stream flow quality associated with a Laminar Flow Control experiment was carried out in the Langley Research Center 8-Foot Transonic Pressure Tunnel (8' TPT). The facility was modified with turbulence manipulators and a liner that provided a flow field around a yawed super-critical airfoil that is conducive to transition research. These devices are evaluated to determine the sources of disturbances associated with the LFC experiment.