Separation of Vortex Shedding Tones and Broadband Signals using SPOD of uPSP Measurements in NASA Ames Wind Tunnel Test

This paper discusses the outputs of Spectral Proper Orthogonal Decomposition (SPOD) of Unsteady Pressure-Sensitive Paint (uPSP) measurements in a Space Launch System (SLS) Force & Moment Test. The uPSP measurements were collected in the transonic wind tunnel with a scale mode of the SLS Block 1 crew vehicle at NASA Ames Research Center in April 2025. Vortex shedding tones, which were generated by the forward attachments of the Solid Rocket Boosters (SRBs) were consistently observed in the uPSP measurements. In this paper, it is demonstrated, with SPOD and Inverse SPOD, the original uPSP measurements are effectively separated into two datasets of timeseries of the vortex shedding tones and broadband signals. The characteristics of the vortex shedding tones are presented through visualization of the SPOD modes. The work described in this paper is a part of NASA’s development of a new state-of-the-art uPSP capability in production wind tunnels. Funding was provided by the NASA Aerosciences Evaluation and Test Capabilities Portfolio Office of the Aeronautics Research Mission Directorate.