Surface pressure fluctuations developed by turbulent flow within a boundary layer is a major cause of flow noise from a body and an issue which reveals itself over a wide range of engineering applications. Modified boundary layers (MBLs) inspired by the down coat of an owl’s wing has shown to reduce the acoustic effects caused by flow noise. This thesis investigates the mechanisms that modified boundary layers can provide for reducing the surface pressure fluctuations in a boundary layer. This study analyzes various types of MBLs in a wall jet wind tunnel through computational fluid dynamics and numerical surface pressure spectrum predictions. A novel surface pressure fluctuation spectrum model is developed for use in a wall jet boundary layer and demonstrates high accuracy over a range of Reynolds numbers. Non-dimensional parameters which define the MBL’s geometry and flow environment were found to have a key role in optimizing the acoustic performance. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

Three-dimensional spheroid arrays represent in vivo activity better than conventional 2D cell culturing. A high-throughput microfluidic chip may be capable of depositing cells into spheroid arrays, but it is difficult to regulate the path of individual cells for deposition. Droplets that encapsulate cells may aid in facilitating cell delivery and deposition in the return bend of a microfluidic chip. In this study, a low-cost method for fabricating polymer-cast microfluidic chips has been developed for rapid device prototyping. Computational fluid dynamic (CFD) simulations were conducted to quantify how a change in geometry or fluid properties affects the dynamics of a droplet. These simulations have shown that the deformation, velocity, and trajectory of a droplet are altered when varying the geometry and fluid properties of a multiphase microfluidic system. This quantitative data will be beneficial for the future design of a microfluidic chip for cell deposition into 3D spheroid arrays.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第23371号 / 医博第4740号 / 新制||医||1051(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 髙橋 良輔, 教授 安達 泰治, 教授 YOUSSEFIAN Shohab / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

This document focuses on the procedure and results of creating a thermohydraulic model of the secondary cooling system of the SAFARI-1 research reactor at the Pelindaba facility of the South African Nuclear Energy Corporation (Necsa) to the west of Pretoria, South Africa. The secondary cooling system is an open recirculating cooling system that comprises an array of parallel-coupled heat exchangers between the primary systems and the main heat sink system, which consists of multiple counterflow-induced draught cooling towers. The original construction of the reactor was a turnkey installation, with no theoretical/technical support or verifiability. The design baseline is therefore not available and it is necessary to reverse-engineer a system that could be modelled and characterised. For the nuclear operator, it is essential to be able to make predictions and systematically implement modifications to improve system performance, such as to understand and modify the control system. Another objective is to identify the critical performance areas of the thermohydraulic system or to determine whether the cooling capacity of the secondary system meets the optimum original design characteristics. The approach was to perform a comprehensive one-dimensional modelling of all the available physical components, which was followed by using existing performance data to verify the accuracy and validity of the developed model. Where performance data is not available, separate analysis through computational fluid dynamics (CFD) modelling is performed to generate the required inputs. The results yielded a model that is accurate within 10%. This is acceptable when compared to the variation within the supplied data, generated and assumed alternatives, and when considering the compounding effect of the large amount of interdependent components, each with their own characteristics and associated performance uncertainties. The model pointed to potential problems within the current system, which comprised either an obstruction in a certain component or faulty measuring equipment. Furthermore, it was found that the current spray nozzles in the cooling towers are underutilised. It should be possible to use the current cooling tower arrangement to support a similar second reactor, although slight modifications would be required to ensure that the current system is not operated beyond its current limits. The interdependent nature of two parallel systems and the variability of the conditions that currently exist would require a similar analysis as the current model to determine the viability of using the existing cooling towers for an additional reactor. / Dissertation (MEng)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

<p>A comprehensive study of inclusion aggregation and removal in different bottom gas-stirred ladles has been conducted. The unsteady, three dimensional, isothermal, multiphase computational fluid dynamics (CFD) model was developed. A ladle with two bottom plugs was used in the study. Effects of plug separation angles (180° and 90°) and argon flow rate combinations (5/5 SCFM, 5/20 SCFM and 20/20 SCFM) were investigated. The whole study can be divided into two parts: first, the flow field, slag eye size and wall shear stress have been studied; second, inclusion aggregation and removal in different ladles have been investigated. In the first part, argon bubble breakup and coalescence has been considered. The slag eye size was validated with plant measurement. When the flow rate increases, the size of slag eye will increase while the wall shear stress increases as well. In the second part, a parametric study of ladle design and argon flow rate on inclusion aggregation and removal has been conducted. Turbulence shear collision shows the most dominant effect on inclusion aggregation. The argon flow rate is positively related to inclusion aggregation and removal. When the argon flow rate is fixed, a larger plug separation angle shows higher inclusion aggregation and removal efficiency. </p><br>

One possible way of solving future energy shortages is by the optimization of our current energy consumption. These optimizations must span all possible fields of consumption. In the mechanical field radial piston hydraulic motors may show some margin of improvement. The radial piston hydraulic motor is driven by a pressure difference in hydraulic oil. These motors are commonly found in heavy industrial equipments such as drills and conveyor belts. The advantage with these motors in comparison with electric motors is the high torque and ability to absorb shock loads that may cause damage to electrical motors. The effectiveness of these motors are determined both by the motor and by the drive system as a whole consisting of hydraulic pump driven by a electric motor, hydraulic hoses, motor and possible external coolers. If the effectiveness of the motor is low the whole drive system will be affected thus amplifying the total losses. The losses in the motor can be both mechanical and derived to the viscosity of the oil. One region in the motor where there are viscous losses are in the housing. The housing is filled with oil, that both aids in the cooling and acts as a lubricant for the motor. Pistons and rollers are some of the components found in the housing. These components rotates around the centre line axis while having a pulsating radial motion following a cam ring. This rotating and pulsating motion will push oil in and out of a volume between two consecutive pistons and rollers. This will create viscous losses and regions with a enhanced risk of cavitation. This study investigates if the flow of oil in the housing can be simulated accurately. The study also examine what are the main problems regarding the flow of oil in the housing and the factors affecting the size of the viscous losses. The study also examines the correlation between viscosity and viscous losses. Finally two different optimizations with the intention of decreasing the viscous losses are compared. The study found that the majority of the viscous losses in the housing can be derived to the flow of hydraulic oil in and out of the volume between two consecutive pistons and rollers. The oil will pass a sharp edge around the cylinder block and a narrow passage under the spacing between the cylinder rows in a two cam ring configured motor. This will create regions with a enhanced velocity and risk of cavitation. The stroke of the motor will greatly affect the effectiveness of the motor especially at a high rotational speed. The viscous losses will be transformed into internal energy, heat, thus increasing the temperature of the oil. A increased temperature will decrease the viscosity and the viscous losses. The viscous losses will vary with 17 % if the viscosity is varied between 20 and 100 cSt. The developed model is not sufficient to determine the viscous losses accurately since the geometry had to be considerably simplified, but can act as a way of comparing different optimizations of the motor. The viscous losses can be decreased with 25 % in the CCe motor at 150 rpm by milling material of the cylinder block between the piston holes. This is an expensive optimization and needs to be justified from a cost-benefit perspective.

<p>The objective of this work is to provide a computational baseline for modelling the flow physics in the tip region of a transonic fan. A transonic fan was donated by Honeywell Aerospace to the Purdue University High-Speed Compressor Research Laboratory for the purposes of studying casing treatments and inlet distortion under the Office of Naval Research Power and Propulsion Program. The purpose of casing treatment is to extend the stall margin of the fan without being detrimental to fan efficiency. Hence, before an effective casing treatment can be designed, understanding the instabilities that lead to stall or surge and understanding the flow field near the rotor tip at different operating conditions is necessary. </p> <p>The behavior of the flow field was studied at design speed using steady simulations for near stall, peak efficiency, and choke operating conditions. The details of the passage shock, tip leakage vortex, and the shock-vortex interaction were investigated. The passage shock moves forward in the rotor passage as the loading increases, until eventually becoming unstarted near stall. The tip leakage vortex convects from the rotor tip leading edge to the pressure side of the adjacent blade, and its trajectory becomes parallel to the rotor inlet plane as the loading increases. The shock-vortex interaction does not cause the tip leakage vortex to breakdown, although distortion of the shock front and diffusion of the tip leakage vortex is significant near stall.</p> <p>To validate this computational model, steady simulations were used to conduct a grid convergence study. A single passage mesh of 8 million elements is sufficient to capture the flow qualitatively, but a mesh of at least 22 million elements is recommended to lower discretization error if quantitative details are important. A brief comparison of turbulence models is made, and the SST model was found to predict stronger radial flows than the BSL-EARSM and BSL-RSM models. However, the SST model still captures the flow features qualitatively, and the more complex models would be too costly for iterative design simulations.</p> <p>The importance of unsteady effects was also considered for a point near peak efficiency. Near peak efficiency, the effect of shock oscillations near the rotor shroud are small. Compared to steady simulations, the unsteady simulation predicts a slightly stronger horseshoe vortex at the hub and a passage shock closer to the rotor leading edge. The tip leakage vortex trajectory appears to be the same between the steady and unsteady simulations.</p> <p>The modelling decisions made in this research are currently only based on comparison between simulations. This model will be calibrated with experimental data in the future to provide a more accurate view of the flow physics inside this transonic fan.</p>

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