| Summary: |
This project is concerned with an experimental investigation of a novel technique that is intended to suppress the vortex-shedding process and thereby enhance the mixing within the UV tank without an increase in energy costs. The technique involves the placement of a small 'control' cylinder in the vicinity of the larger cylinder (the UV source). It is known from some direct numerical simulations that the presence of such a 'control' cylinder strongly modifies the flow dynamics and can lead to either suppression or enhancement of the shedding intensity, depending on its size and location relative to the large cylinder. The effects of this 'control' cylinder also depend strongly on the flow Reynolds number. In this particular case, our interest lies in the suppression of the vortex-shedding, while simultaneously enhancing the turbulence mixing to ensure that minimum levels of dosage and exposure times are met. In this project, we will experimentally investigate in detail the flow of Newtonian and some non-Newtonian fluids around a single cylinder with a control cylinder positioned at various locations around it in order to map systematically the conditions for vortex suppression and provide data for validation of calculations.
The diameter of the main cylinder will be of the order of 20 mm and that of the control cylinder will be of the order of 3 mm. The control cylinder will be placed close to or inside the boundary layer of the main cylinder, but at various angles of around 90° from the stagnation point. The following cases will be investigated: (1) flow of water, possibly a viscous Newtonian fluid, and non-Newtonian waste water analogues around a single cylinder to act as a reference case; (2) flow of the same Newtonian and non-Newtonian fluids around a main cylinder with a control cylinder at various locations around the large cylinder to assess its effect on the intensity of vortex shedding; (3) flow of the Newtonian and non-Newto  |
Summary
This project is concerned with an experimental investigation of a novel technique that is intended to suppress the vortex-shedding process and thereby enhance the mixing within the UV tank without an increase in energy costs. The technique involves the placement of a small 'control' cylinder in the vicinity of the larger cylinder (the UV source). It is known from some direct numerical simulations that the presence of such a 'control' cylinder strongly modifies the flow dynamics and can lead to either suppression or enhancement of the shedding intensity, depending on its size and location relative to the large cylinder. The effects of this 'control' cylinder also depend strongly on the flow Reynolds number. In this particular case, our interest lies in the suppression of the vortex-shedding, while simultaneously enhancing the turbulence mixing to ensure that minimum levels of dosage and exposure times are met. In this project, we will experimentally investigate in detail the flow of Newtonian and some non-Newtonian fluids around a single cylinder with a control cylinder positioned at various locations around it in order to map systematically the conditions for vortex suppression and provide data for validation of calculations.
The diameter of the main cylinder will be of the order of 20 mm and that of the control cylinder will be of the order of 3 mm. The control cylinder will be placed close to or inside the boundary layer of the main cylinder, but at various angles of around 90° from the stagnation point. The following cases will be investigated: (1) flow of water, possibly a viscous Newtonian fluid, and non-Newtonian waste water analogues around a single cylinder to act as a reference case; (2) flow of the same Newtonian and non-Newtonian fluids around a main cylinder with a control cylinder at various locations around the large cylinder to assess its effect on the intensity of vortex shedding; (3) flow of the Newtonian and non-Newtonian fluids across a single row of cylinders mimicking the exact flow condition in an industrial tank, with all cylinders having a control cylinder; (4) flow of the Newtonian and non-Newtonian fluids across an array of cylinders as in an industrial tank, with all cylinders having a control cylinder for the situation that showed the better performance with a single row.
The experiments will be carried out in the 400 liter closed water circuit of CEFT-FEUP, after installing a new test section and some minor improvements in the tunnel. To quantify the effects of the control cylinder, it will be necessary to measure the streamwise profile of the transverse Reynolds normal stress along the centerline of the main cylinder, the spectrum of the instantaneous streamwise velocity fluctuations and the pressure on the cylinder surface from which to deduce the frequency of the vortex shedding and the extent of flow modification wrought by the introduction of the control cylinder. The streamwise velocity and the Reynolds normal stress will be measured using a laser- Doppler anemometer and for the former the measured data will be FFT processed. Maps of the instantaneous flow will also be measured by PIV in order to better assess the interference due multiple cylinders. To select the appropriate non-Newtonian fluids the rheology of waste water will be measured in rotational and capillary breakup rheometers in order for the selected analogue fluid to have a rheology as close as possible to those of the waste water.
This project will benefit from the on-going collaboration with Professor BA Younis from the Department of Civil and Environmental Engineering of the University of California - Davis, who is also a consultant in this project.
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