Document
uPSP Test Technology
Capability Challenge
Separation of Vortex Shedding Tones and Broadband Signals using SPOD of uPSP Measurements in NASA Ames Wind Tunnel Test 1 2 2 2 2 Jie Li , E. Lara Lash , Kenneth R. Lyons , David D. Murakami , Nettie H. Roozeboom , 2 1 2 2 Marc A. Shaw - Lecerf , Evan D. Crowe , Nathan W.C. Eller , Sofia Y. Tafolla Metis Technology Solutions, Inc., Moffett Field, CA 94035 NASA Ames Research Center, Moffett Field, CA 94035 2026 AIAA SciTech Forum, Orlando, Florida January 12 - 16, 2026
Introduction
• Unsteady Pressure - Sensitive Paint
( uPSP ) measurements were
collected in a Force & Moment Test
of the Space Launch System (SLS)
Block 1 crew vehicle at NASA Ames
Research Center in April 2025.
• This paper discusses separation of
vortex shedding tones and
broadband signals using Spectral
Proper Orthogonal Decomposition
(SPOD) of the uPSP measurements.
Scale Model of the SLS Block 1 Crew Vehicle in the Force & Moment Test in April 2025
Vortex Shedding Tones
• Vortex shedding tones, generated by the forward attachments of
the Solid Rocket Boosters (SRBs), were consistently observed in
the uPSP measurements .
Right SRB
Center Body
Left SRB
Selected Grid Nodes and Patches
Reference Patch Left SRB Forward Areas of Camera Attachments View Blockage of SRBs b y SRBs Right SRB
SPOD and Inverse SPOD Algorithms
• SPOD of uPSP measurements
• Full timeseries of uPSP measurements are partitioned into a set of smaller blocks, and each block is converted from the time domain to the frequency domain with the Discrete Fourier Transform (DFT); • A t each frequency, the Cross Spectral Density (CSD) matrix is estimated with Welch’s method, and the SPOD modes are determined as the eigenvectors of the estimated CSD matrix .
• Inverse SPOD
• Dominant SPOD modes are converted from the frequency domain to the time domain.
Energy of SPOD Modes at Mach 1.2
Energy of SPOD modes of uPSP measurements on selected grid nodes at Mach 1.2 Vortex Shedding Tone Vortex Shedding Tone st st 1 Harmonic 1 Harmonic Left SRB Right SRB Vortex Shedding Tone Vortex Shedding Tone nd nd 2 Harmonic 2 Harmonic Right SRB Left SRB
Separation of Vortex Shedding Tones and Broadband Signals (1)
Original uPSP Vortex Shedding Broadband
Measurements Tones Signals
Timeseries of
Average
Pressures
Vortex Shedding Tone Vortex Shedding Tone st nd 1 Harmonic, Left SRB 2 Harmonic, Left SRB
Power Spectral
Densities
(PSDs)
Separation of Vortex Shedding Tones and Broadband Signals (2)
Original uPSP Vortex Shedding Broadband
Measurements Tones
Signals
Vortex Shedding Tone nd 2 Harmonic Left SRB Vortex Shedding Tone st 1 Harmonic Left SRB
Visualization of SPOD Modes of Vortex Shedding Tones in Frequency Domain
Magnitude (psi) of SPOD Modes Energy (psi ) of SPOD Modes Vortex Shedding Tone Vortex Shedding Tone st st 1 Harmonic 1 Harmonic Vortex Shedding Tone Vortex Shedding Tone Reference Left SRB Right SRB st st 1 Harmonic 1 Harmonic Frequency st st 1 SPOD Mode 1 SPOD Mode Left SRB Right SRB nd nd 2 SPOD Mode 2 SPOD Mode
Visualization of SPOD Modes of Vortex Shedding Tones in Time Domain
st 1 SPOD Modes of Vortex Shedding Tones of Left SRB st st 1 SPOD Mode, 1 Harmonic Raw uPSP Measurements st nd 1 SPOD Mode, 2 Harmonic
Conclusions
• The outputs of SPOD of uPSP measurements of an SLS Force & Moment
Test are discussed.
• It is demonstrated the vortex shedding tones can be effectively separated
from the broadband signals in the time domain using the Inverse SPOD of
the dominant SPOD modes of uPSP measurements.
• Different aerodynamic and aeroacoustic phenomena may be analyzed separately.
• The characteristics of the vortex shedding tones are presented through
visualization of the SPOD modes.
• The measurements of uPSP have much higher spatial resolution compared to those of the conventional pressure transducers.
Acknowledgement
• Funding was provided by the NASA Aerosciences Evaluation and Test Capabilities (AETC) Portfolio Office .
• Many thanks to the SLS team .
• The authors highly appreciate the contributions of all member of the team .
NASA Ames Research Center NASA Marshall Space NASA Langley Fluid Mechanics Unitary Plan NASA Advanced Flight Center Research Center Lab Wind Tunnel Supercomputing Ryan Connelly Michael Barad Oleg Goushcha Max Amaya Avraham Gileadi Bruce LaVerde Stephen Cotton Patrick Heaney Jennifer Baerny Lawrence Hand Thomas Steva Derek Dalle Seth Kelly James Bell Andrew Meade Cory Wilbanks David Ellsworth David Piatak Colin Davis Rabindra Mehta Timothy Wray Christopher Henze Jeremy Pinier Maureen Delgado Blair Maclachlan Jeffrey Housman James Ramey Jennifer Everett Jayanta Panda Nina McCurdy Martin Sekula Ross Flach James Ross Patrick Moran Patrick Shea Theodore Garbeff Nathanial Smith Bron Nelson Francesco Soranna Samuel Morice Timothy Sandstrom Craig Streett James Prunty Gerrit - Daniel Stich Hannah Spooner Boeing Tim Steiger AeroHydroPLUS Mike Treece Thomas Volden Paul Bremner Jaffar Iqbal Michael Weiss Alan Landman