Turbulence is known to be a critical mechanism in mass transfer, mixing and dissipation of energy and crucial to understanding the hydrodynamic process in our oceans. In the near coastal environment high tidal forcing around land masses and in coastal channels causes high flow rates and fully developed turbulent regimes. Interaction of this flow with the bathymetry creates coherent turbulent structures. This process can be described by the turbulent kinetic energy budget, which includes the production, advection and dissipation components. Understanding and defining these components is vital in the application of knowledge to marine processes. For example the dissipation and production terms are critical to the numerical representation of flows in the Reynolds Averaged Navier-Stokes equations (RANS) and understanding of their temporal and spatial variation in connection to sediment transport mechanisms and ecological interactions.
The research project will investigate the use of Acoustic Doppler Current Profilers (ADCPs) and Acoustic Doppler Velocimetry (ADV) in the analysis of turbulence structures and measurement metrics in high flow environments (Reynolds stresses, TKE dissipation). ADCP technology (typically diverging beams) is well developed for capturing velocities in oceanic and coastal environments (Guerra, M. and Thomson, J. 2017). However, it is recognised that best-practise for application at energetic sites requires further progress, particularly in their application for turbulence characterisation. Some work has been undertaken to characterise and propagate uncertainties in ADCP measurements in high-flow sites (Rathnayake et al., 2020) however further work is required in characterisation of turbulent structures.
The project will enhance existing field measurement methodologies using a numerical twin of the measurement technique. This will be established using computational fluid dynamics tools such as OpenFoam. The domain will model the bathymetric features of an idealised and then well characterised high flow environment such as Strangford Narrows. Using high fidelity turbulence models such as Large or Detached Eddy Simulation (LES/ DES) and synthetic eddy generation models a statistically representative flow environment will be replicated in the numerical domain. Once established the simulation will be used to take virtual Acoustic Doppler Current Profiler (vADCP) measurements and derive known turbulence metrics verses derived measurements using the vADCP tool. The investigation will provide insight into uncertainty propagation for flow and turbulence metrics. This will be a novel application of vADCP concept and will further understanding and limitations of ADCP measurement techniques at these sites (Mercier et al, 2021).
Once an understanding of the limitations of the existing methodologies is established, enhanced methods increasing confidence in the derived measurements from Acoustic Doppler Current Profiler (ADCP) deployment will be demonstrated at the site of investigation. Anticipated outcomes include best-practise guidance or standards for ADCP instruments usage in derived turbulence measurement, novel techniques for uncertainty propagation in derived measurements. In energetic, high-flow sites this will increase understanding of turbulent interactions and their characterisation as part of furthering marine processes research.
- Background and recent relevant experience in oceanography, marine science, marine geoscience or marine engineering
- Knowledge of fluid mechanics/ hydrodynamics, turbulence, and tides
- Team player, willing to support other field work at Queen’s Marine Laboratory
- Willingness to travel locally (Belfast to Portaferry) and to international conferences
- Knowledge and use of Acoustic Doppler Instrumentation
- Experience in field measurement campaigns in the marine environment
- Experience with OpenFoam software, Linux OS and HPC clusters
Photo credit: Carwyn Frost, QUB
Guerra, M. and Thomson, J. (2017) ‘Turbulence measurements from five-beam acoustic doppler current profilers’, Journal of Atmospheric and Oceanic Technology, 34(6), pp. 1267–1284. doi: 10.1175/JTECH-D-16-0148.1.
Rathnayake, U., Folley, M., Gunawardane, S.D.G.S.P., Frost, C., (2020) ‘Investigation of the Error of Mean Representative Current Velocity Based on the Method of Bins for Tidal Turbines Using ADP Data’. J. Mar. Sci. Eng. 8, 390. https://doi.org/10.3390/jmse8060390
Philippe Mercier, Maxime Thiébaut, Sylvain Guillou, Christophe Maisondieu, Emmanuel Poizot, Aline Pieterse, Jérôme Thiébot, Jean-François Filipot, Mikaël Grondeau. (2021) ‘Turbulence measurements: An assessment of Acoustic Doppler Current Profiler accuracy in rough environment’. Ocean Engineering, Volume 226, 108819, ISSN 0029-8018, https://doi.org/10.1016/j.oceaneng.2021.108819
To be confirmed