Three-Velocity-Component Cross-Correlation Doppler Global Velocimetry for the Space Launch System Booster Separation Test in the NASA Langley Unitary Plan Wind Tunnel

The biases introduced by background light contributions in planar, Doppler-based velocimetry are significantly reduced by the application of structured illumination. The method works by measuring and separating desired flow-scattered signals from unwanted reflections and secondary scattering contributions via a sinusoidal intensity modulation across the laser sheet used to interrogate the flow. In the current work we consider the influence of background light on cross-correlation Doppler global velocimetry (CC-DGV) and present the results for measurements in a turbulent free jet with an exit Mach number of 0.5 in a measurement arrangement with high intensity background contributions. It is shown that if the ratio of the particle-scattering (i.e. Mie scattering) intensity to the background solid surface scattering (i.e. geometric scattering) intensity is greater than 10, then the measured signal displays a significant bias away from the true velocity. With structured illumination, the measured intensity corresponding to geometric scattering is reduced to negligible levels, reminiscent of a measurement arrangement with little or no background light influence. Centreline velocity measurements with this background subtraction method are compared with Kiel-type pressure probe measurements, yielding a root-mean-square (RMS) difference between the two of 1.2 m s -1 (less than 1% of the full scale velocity), well within the published uncertainty bound of the CC-DGV technique, underscoring the robustness of this approach. In addition to the centreline validation, the streamwise vorticity and total pressure are also analysed, showing trends indicative of the S-type shape of the duct and aggressive flow entrainment experienced in this environment.

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“…5,22], provide ample motivation for improving the technique with background removal techniques such as structured illumination.…”

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confidence: 99%

Geometric scattering removal in cross-correlation Doppler global velocimetry by structured illumination

Boyda¹,

Byun²,

Saltzman³

et al. 2020

Meas. Sci. Technol.

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Space Launch System Booster Separation Supersonic Powered Testing with Surface and Off-body Measurements

Winski

Danehy

Watkins

et al. 2019

AIAA Aviation 2019 Forum

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A wind tunnel test was run in the NASA Langley Unitary Plan Wind Tunnel simulating the separation of the two solid rocket boosters (SRB) from the core stage of the NASA Space Launch System (SLS). The test was run on a 0.9% scale model of the SLS Block 1B Cargo (27005) configuration and the SLS Block 1B Crew (28005) configuration at a Mach of 4.0. High pressure air was used to simulate plumes from the booster separation motors located at the nose and aft skirt of the two boosters. Force and moment data were taken on both SRBs and on the core stage. Schlieren still photos and video were recorded throughout testing. A set of points were acquired using Cross-correlation Doppler Global Velocimetry (CCDGV) readings to get 3 component velocity measurements between the core and the left-hand SRB. The CCDGV laser was utilized to record flow visualization in the same location, between the core and the left-hand SRB. Pressure Sensitive Paint data were taken on a separate set of runs. Computational Fluid Dynamics (CFD) runs were computed on a subset of the wind tunnel data points for comparison. A combination of the force/moment, CCDGV and Pressure Sensitive Paint (PSP) data (as well as schlieren images) at the CFD-specified test conditions will be used to validate the CFD simulations that will be used to build an SLS booster separation database at flight conditions.Notice to the Reader -The Space Launch System, including its predicted performance and certain other features and characteristics, has been defined by the U.S. Government to be Sensitive But Unclassified (SBU). Information deemed to be SBU requires special protection and may not be disclosed to an international audience. To comply with SBU restrictions, details such as absolute values have been removed from some plots and figures in this paper. It is the opinion of the authors that despite these alterations, there is no loss of meaningful technical content.

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Velocity measurements across an oblique shock using pulse-burst cross-correlation DGV

Burns

Fahringer

Danehy

2021

AIAA Scitech 2021 Forum

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Three-Velocity-Component Cross-Correlation Doppler Global Velocimetry for the Space Launch System Booster Separation Test in the NASA Langley Unitary Plan Wind Tunnel

Cited by 5 publications

References 4 publications

Geometric scattering removal in cross-correlation Doppler global velocimetry by structured illumination

Geometric scattering removal in cross-correlation Doppler global velocimetry by structured illumination

Space Launch System Booster Separation Supersonic Powered Testing with Surface and Off-body Measurements

Velocity measurements across an oblique shock using pulse-burst cross-correlation DGV

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