Demonstration of a Temperature-Compensated Pressure Sensitive Paint on the Orion Launch Abort Vehicle (Invited)

Abstract

Engineers at the Arnold Engineering Development Center (AEDC) have been developing a pressure-sensitive paint (PSP) capability for the Propulsion Wind Tunnel (PWT) 16T to acquire surface pressure data on wind tunnel models. Some advantages of using PSP are: 1) it provides a more complete pressure distribution than is possible with individual pressure orifices and 2) it permits the acquisition of data in areas inaccessible to conventional pressure measurements. In addition, PSP data can easily be integrated over individual surfaces to determine distributed loads. NASA Ames had a requirement to measure the aerodynamic surface pressure distribution on the Orion Launch Abort Vehicle (LAV) in the wind tunnel to determine distributed loads, but the model design would not allow installation of a sufficient number of pressure orifices. Therefore, NASA requested that AEDC provide their PSP capability for wind tunnel tests at the Ames Research Center in the 11-ft transonic and 9x 7-ft supersonic wind tunnels. The test article had two high-pressure airflow paths internal to the model to provide simulated exhaust from the abort motors (AM) and attitude control motors (ACM). The AM flow required the air to be heated to 110F to avoid liquefaction during expansion from the nozzles while the ACM flow was not heated. Unfortunately, the PSP extensively used at AEDC has some temperature sensitivity, albeit small. This has not been a problem for tests in 16T because the model surface temperature typically reaches equilibrium with the tunnel flow and any small variations in temperature (<4F) are of little impact. However, use of the traditional PSP for the Orion LAV test, with the expected large temperature variations, would result in significant pressure measurement errors. A new binary PSP with self-compensation for temperature was developed and applied to the Orion LAV for tests in both wind tunnels. The new PSP had significantly less temperature sensitivity than the traditional AEDC PSP, and a comparison of the paint performance is presented. Images from an infrared camera documented the range of surface temperature variations and assisted in evaluating the performance of the new paint. The largest temperature variation detected would have resulted in pressure errors greater than 100 psf (depending on the absolute pressure value). Analysis of the PSP uncertainty, determined using conventional pressure measurements as the standard, indicate the average uncertainty to be 10-15 psf. Comparisons are made between PSP and conventional pressure measurements and integrations of the PSP and the internal balance. The full model surface pressure distributions are presented to aid in understanding the data.