The ability to scale the field of view for velocimetry methods is particularly attractive for aeroacoustics studies, where turbulence contributions in long-lived, low wavenumber structures account for the most important sources of radiated noise. Thanks to its core operating principles, Doppler global velocimetry (DGV) offers interesting opportunities for large-scale flow measurements. As is well known, a larger field-of-view (FOV) in the measurement will change the spatial resolution, meaning that each measurement is integrated across a larger control volume. This finite size will affect the velocity and turbulence measurements, as well as the observable wavenumbers in the measurement. The present study confirms the viability of DGV for studying low wavenumbers while examining the influence on higher wavenumbers of the less coherent turbulent structures also present in high-speed flows. In the flows examined by the current work, mean velocity bias error due to integration over the measurement region was shown to be small, less than 0.005%, for control volume heights up to 4 mm. Although significant energy attenuation occurs for high wavenumbers, the low wavenumber turbulent structures which dominate far-field noise are found to be unaffected by the size of the control volume required for large measurement of both laboratory- and full-scale supersonic jet flows. The results indicate a large-scale velocimetry system such as DGV can be a valuable tool for researchers to study aeroacoustics in high-speed flows.
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Saltzman, A.J., Lowe, K.T. & Ng, W.F. Finite control volume and scalability effects in velocimetry for application to aeroacoustics. Exp Fluids 62, 33 (2021). https://doi.org/10.1007/s00348-021-03138-2