Magnetic resonance velocimetry in high‑speed turbulent flows

Magnetic resonance velocimetry in high‑speed turbulent flows: sources of measurement errors and a new approach for higher accuracy

John, Kristine (Universität Rostock)
Jahangir, S. (TU Delft Fluid Mechanics)
Gawandalkar, U.U. (TU Delft Multi Phase Systems)
Hogendoorn, W.J. (TU Delft Multi Phase Systems)
Poelma, C. (TU Delft Multi Phase Systems)
Grundmann, Sven (Universität Rostock)
Bruschewski, Martin (Universität Rostock)

2020

This study focuses on the measurement accuracy of Magnetic Resonance Velocimetry (MRV) in high-speed turbulent flows. One of the most prominent errors in MRV is the displacement error, which describes the misregistration of spatial coordinates and velocity components in moving fluids. Displacement errors are particularly critical for experiments with high flow velocity and high spatial resolution. The degree of displacement error also depends on the sequence structure of the MRV technique. In this study, two MRV sequence types are examined regarding their measurement capabilities in high-speed turbulent flows: a conventional MRV sequence based on the popular “4D FLOW” technique, and a newly developed sequence, named “SYNC SPI”. Compared to conventional MRV, SYNC SPI is designed for high measurement accuracy, and not for imaging speed, which limits its application to statistically stationary flows. Both sequence types are evaluated in a flow experiment with a converging–diverging nozzle. Time-averaged results are presented for velocities up to 12 m/s at the throat. Supported by Particle Imaging Velocimetry, it is shown that SYNC SPI is capable of acquiring accurate velocity data in these highly turbulent flows. In contrast, the data from the conventional MRV sequence exhibits substantial displacement errors with a maximum displacement of 21 mm. The long acquisition time is the main disadvantage of the SYNC SPI sequence. Therefore, it is examined if undersampling and non-linear reconstruction, known as Compressed Sensing, can be utilized to make data acquisition more efficient. In the presented measurements, Compressed Sensing is successfully applied to shorten the acquisition time by up to 70% with almost no reduction in measurement accuracy.

http://resolver.tudelft.nl/uuid:6072d654-f7c5-46a6-b75b-620a05088cc0

https://doi.org/10.1007/s00348-019-2849-4

2020-07-14

0723-4864

Experiments in Fluids: experimental methods and their applications to fluid flow, 61 (2)

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2020 Kristine John, S. Jahangir, U.U. Gawandalkar, W.J. Hogendoorn, C. Poelma, Sven Grundmann, Martin Bruschewski