Wake hydrodynamics downstream from a horizontal axis turbine under current flow and waves

Due to concerns over the potential impacts of climate change on the environment, there is a growing interest in developing renewable forms of energy. Tidal streams are a potential source of renewable energy that can be harnessed for electricity generation using tidal stream turbines. However, due to the technology being a relatively new development, with limited testing and commercial applications, the flow dynamics and environmental impact of such devices is still poorly understood.This research investigates the flow dynamics downstream from a horizontal axis tidal stream turbine device using a physical modelling experiment in the Total Environment Simulator laboratory flume, using a channel which measured 11m long, 1.6m wide and 0.6m deep. Detailed flow measurements were collected using a two-camera submersible Particle Image Velocimetry (PIV) system to quantify the three-dimensional flow velocities and turbulence downstream from the model tidal turbine device. A wide range of rotor positions and flow conditions were tested, including current flow and combined wave-current flows. The data collected will be used to validate numerical models developed by project partners, which will assist with developing full-scale operational tidal stream turbines.The presence of the tidal stream turbine within the channel had a significant impact on the flow downstream. A significant velocity deficit was observed in the wake of the turbine. This was particularly skewed, owing to the turbine rotation, to the right hand side of the centreline, where the deficit was greater than the left hand side. Subjecting the turbine to wave-current flow reduced this deficit considerably, with the shortest wake length occurring under the troughs of waves. Positioning the turbine closer to the bed resulted in a substantial increase in shear stress, with vertical and horizontal asymmetry observed in the wake of the turbine and horizontal asymmetry observed in the resulting scour below the turbine.The work outlines the impact of these variables on seafloor scour and integrity, and highlights and discusses the optimisation of turbine efficiency with minimal wake and seafloor scour impacts

An investigation of the wake recovery of two model horizontal-axis tidal stream turbines measured in a laboratory flume with Particle Image Velocimetry

© 2017 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. The uptake of tidal stream-turbine (TST) technology lags other renewable energy sources despite the advantages of predictability, stability and increased power output in comparison to wind turbines of the same dimensions. There remains a need to address environmental concerns about the potential impacts of TSTs including the suspension and deposition of bed sediments if TSTs are to be more widely accepted and deployed. Sediment mobilisation and persistent flow vortices will also adversely affect the performance of other TST devices in an array downstream of the wake. The focus of this work is to improve our understanding of the wake recovery structure of a TST to build on the limited field and laboratory data currently available in order better predict the impact of TSTs on flow and sediment transport. Detailed measurements of the wake flow structures generated by scaled TST devices are presented. These results are the first to be derived from the application of high spatial resolution stereoscopic Particle Image Velocimetry (PIV). Two scale model horizontal-axis TSTs were manufactured and deployed in a laboratory flume (11. m long, 1.6. m wide and 0.6. m deep) at different flow speeds and heights above the bed. The results demonstrate greater wake recovery lengths for the rotor design with wider blade tips, despite the higher wake turbulence generated by the blades. Wake recovery is more rapid at the higher flow speed when greater turbulence from the tips is observed, but wake recovery lengths increase when both rotors are positioned closer to the bed

Modelling impacts of tidal stream turbines on surface waves

© 2018 Elsevier Ltd A high resolution Computational Flow Dynamics (CFD) numerical model is built based on a laboratory experiment in this research to study impacts of tidal turbines on surface wave dynamics. A reduction of ∼3% in wave height is observed under the influence of a standalone turbine located 0.4 m from the free surface. The artificial wave energy dissipation routine ‘OBSTACLE’ within FVCOM is shown to effectively capture the correct level of wave height reduction, reproducing the CFD results with significantly less computational effort. The turbine simulation system is then applied to a series of test cases to investigate impact of a standalone turbine on bed shear stress. Results suggest an apparent increase in bed stress (∼7%) upstream of the turbine due to the inclusion of surface waves. However, in the immediate wake of the turbine, bed stress is dominated by the presence of the turbine itself, accounting for a ∼50% increase, with waves having a seemingly negligible effect up to 9D (D is the turbine diameter) downstream of the turbine. Beyond this point, the effect of waves on bed shear stress become apparent again. The influence of OBSTACLE on bed stress is also noticeable in the far wake, showing a reduction of ∼2% in wave height

Modelling tidal stream turbines in a three-dimensional wave-current fully coupled oceanographic model

© 2017 The Author(s) A tidal turbine simulation system is developed based on a three-dimensional oceanographic numerical model. Both the current and turbulent controlling equations are modified to account for impact of tidal turbines on water velocity and turbulence generation and dissipation. High resolution mesh size at the turbine location is assigned in order to capture the details of hydrodynamics due to the turbine operation. The system is tested against comprehensive measurements in a water flume experiment and results of Computational Fluid Dynamics (CFD) simulations. The validation results suggest that the new modelling system is proven to be able to accurately simulate hydrodynamics with the presence of turbines. The developed turbine simulation system is then applied to a series of test cases in which a standalone turbine is deployed. Here, complete velocity profiles and mixing are realized that could not have been produced in a standard two-dimensional treatment. Of particular interest in these cases is an observed accelerated flow near the bed in the wake of the turbine, leading to enhanced bottom shear stress (∼2 N/m 2 corresponding to the critical stress of a range of fine gravel and finer sediment particles)

Three-dimensional modelling of suspended sediment transport in the far wake of tidal stream turbines

A three-dimensional tidal turbine simulation based on an oceanographic numerical model has been tested for suspended sediment calculation, particularly in the wake of a standalone tidal turbine. The results suggest a need for further improvement of the model in order to obtain correct predictions of suspension strength of the wake and suspended sediment concentration under the influence of a turbine (compared to measured data). Due to the wide use of FVCOM in coastal applications where turbines are commonly installed, it proves necessary to address this issue. Two approaches with respect to modifying bed shear stress and turbulent mixing calculations in the presence of a turbine are proposed and tested in this research. Using data collected in the laboratory as reference, the turbulent mixing enhancement approach is shown to be effective. A series of tests are carried out to identify the impact of the turbine on suspended sediment transport in its vicinity. The results suggest that the impact is highly dependent upon the sediment grain size

Movement Interventions for Children with Autism and Developmental Disabilities: An Evidence-Based Practice Project

This review explored the following question: Are the comprehensive treatment models Makoto Therapy, Brain Gym, and Interactive Metronome effective interventions for improving occupational performance including improving executive function, academic performance, and physical coordination in children and adolescents with Autism Spectrum Disorder (ASD)? Because current research on Interactive Metronome, Brain Gym®, and Makoto Therapy fails to address children and adolescents with autism spectrum disorder, presents multiple flaws in research design, and does not measure occupational outcomes such as occupational performance, we recommend that these interventions should not be used as comprehensive treatment models in occupational therapy. We recommend that more occupational-based, methodologically-sound research involving youth with ASD be conducted before implementing these interventions in occupational therapy practice

Consensus-Based Evaluation of Outcome Measures in Pediatric Stroke Care: A Toolkit

Following a pediatric stroke, outcome measures selected for monitoring functional recovery and development vary widely. We sought to develop a toolkit of outcome measures that are currently available to clinicians, possess strong psychometric properties, and are feasible for use within clinical settings. A multidisciplinary group of clinicians and scientists from the International Pediatric Stroke Organization comprehensively reviewed the quality of measures in multiple domains described in pediatric stroke populations including global performance, motor and cognitive function, language, quality of life, and behavior and adaptive functioning. The quality of each measure was evaluated using guidelines focused on responsiveness and sensitivity, reliability, validity, feasibility, and predictive utility. A total of 48 outcome measures were included and were rated by experts based on the available evidence within the literature supporting the strengths of their psychometric properties and practical use. Only three measures were found to be validated for use in pediatric stroke: the Pediatric Stroke Outcome Measure, the Pediatric Stroke Recurrence and Recovery Questionnaire, and the Pediatric Stroke Quality of Life Measure. However, multiple additional measures were deemed to have good psychometric properties and acceptable utility for assessing pediatric stroke outcomes. Strengths and weaknesses of commonly used measures including feasibility are highlighted to guide evidence-based and practicable outcome measure selection. Improving the coherence of outcome assessment will facilitate comparison of studies and enhance research and clinical care in children with stroke. Further work is urgently needed to close the gap and validate measures across all clinically significant domains in the pediatric stroke population

Stromal Cells Covering Omental Fat-Associated Lymphoid Clusters Trigger Formation of Neutrophil Aggregates to Capture Peritoneal Contaminants

The omentum is a visceral adipose tissue rich in fat-associated lymphoid clusters (FALCs) that collects peritoneal contaminants and provides a first layer of immunological defense within the abdomen. Here, we investigated the mechanisms that mediate the capture of peritoneal contaminants during peritonitis. Single-cell RNA sequencing and spatial analysis of omental stromal cells revealed that the surface of FALCs were covered by CXCL1+ mesothelial cells, which we termed FALC cover cells. Blockade of CXCL1 inhibited the recruitment and aggregation of neutrophils at FALCs during zymosan-induced peritonitis. Inhibition of protein arginine deiminase 4, an enzyme important for the release of neutrophil extracellular traps, abolished neutrophil aggregation and the capture of peritoneal contaminants by omental FALCs. Analysis of omental samples from patients with acute appendicitis confirmed neutrophil recruitment and bacterial capture at FALCs. Thus, specialized omental mesothelial cells coordinate the recruitment and aggregation of neutrophils to capture peritoneal contaminants