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2D PIV experiments of oscillatory flow in a stenosis : a study into the physics of flow of cerebrospinal fluid

Busink, K. (2021) 2D PIV experiments of oscillatory flow in a stenosis : a study into the physics of flow of cerebrospinal fluid.

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Abstract:Cerebrospinal fluid (CSF) serves several key functions in the central nervous system (CNS), as it protects the brain and spinal cord, clears waste and transports nutrients. Researchers established links between neurological conditions and the flow and composition of CSF. Although these discoveries indicate the importance of CSF, the flow dynamics are still poorly understood. The complex geometry of the brain can even lead to a transition to turbulence in the flow of CSF. In the first part of this research a setup was built and characterized that is representative for the flow of CSF. In the second part oscillatory flow experiments in a stenosis were conducted, to study the flow dynamics and investigate the transition to turbulence. As CSF is considered an oscillating flow with a zero mean, a setup had to be designed that is able to create this type of flow and that can capture the velocity components. The highest obtained Reynolds number in the experiments is 2200, although no signs of a transition to turbulence are observed. The Reynolds number is too low or there is lack of a disturbance, which can be a distorted waveform or geometry, and thus turbulence is not yet triggered in the flow. In the second part of the research, experiments in an axisymmetric stenosis of 75% were performed. The setup that is built in the first section is used to conduct these experiments and study the possible transition to turbulence. A jet is formed, which breaks down in between 2 and 3 diameters downstream of the stenosis and this locations shifts closer to the stenosis throat with increasing Reynolds number. The centerline velocities have been used to plot the power spectral density, and based on these results it cannot be be said conclusively if the flow is in the transitional regime. However, it is clear that at Re> 2000, the flow can be referred to as non-laminar. An oscillatory flow was created and the velocity field was quantified by using laser PIV. The flow physics were studied in different configurations and it was feasible to conduct experiments up to Reynolds numbers of 2200. After the introduction of the stenosis, a jet formed downstream of the stenosis. As the conditions in the experiments are not perfect and inaccuracies are introduced into the axisymmetric stenosis, this influences the jet breakdown location and lowers the critical Reynolds number at which the flow transitions. In future experiments the setup can be further optimized and more physiological effects of CSF can be implemented, to further increase the knowledge of this flow.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:33 physics, 50 technical science in general, 52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Link to this item:http://purl.utwente.nl/essays/87410
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