Invited: Error Estimation for Unsteady Pressure Sensitive Paint Measurements

The Unsteady Pressure Sensitive Paint (uPSP) team at NASA Ames uses the lifetime method to measure steady pressures and the intensity method to obtain the unsteady (fluctuating component) of pressure. As with any measurement, it is also important to understand the associated levels of uncertainty. This paper presents a method to propagate the main error sources through the working equations for steady and unsteady pressure measurements, for both the lifetime method and intensity method, and generate uncertainty estimates. Having such estimates is important for test planning purposes and for data quality checks. Two forms of errors are considered. Random error originates mostly from shot noise and read noise inherent in the camera system and manifests as a root-mean-square error in steady pressure measurements or a noise floor in power spectral densities generated from unsteady pressure measurements. Bias error originates mostly from uncertainties in surface temperature and paint calibration and is observed as an offset relative to static pressure tap and pressure transducer measurements. These error sources are discussed, including the behavior of the cameras and the paint, and a tool for estimating error is developed. This estimation method is then compared to measurements from pressure transducers obtained in the Launch Vehicle Demo Test (LVDT), a large scale uPSP wind tunnel test performed in the Ames 11-Foot Transonic Wind Tunnel.