This study analyzed the ability of computational fluid dynamic software to accurately predict the flow coefficient of three bottom-load ball valves to develop a design which can accurately control flow rate.

D.Ing. (Mechanical Engineering) / Most coal fired power stations in South Africa are equipped with Electrostatic Precipitators (ESP's). With the ongoing reduction of allowable emissions, as negotiated with the Chief Air . Pollution Control Officer (CAPCO) of the Department of Environmental Affairs and Tourism (DEAT), ways to reduce emissions are sought. In the case of emission levels exceeding the values set by the controlling authority load losses are required for compliance. This however has the effect of plant operating inefficiently and a loss of revenue will result. Specifically in times of growing demand, when more and more of the currently installed generation capacity is required to satisfy the demand, forced load reductions are not desirable. Performance enhancement of ESP's can be achieved by means of system optimisation. Research was initiated to achieve the capability of modelling important dynamic aspects of ESP performance using Computational Fluid Dynamics (CFD). This modelling capability would create the opportunity to investigate the different influencing factors which govern the dust collection efficiency. In the past ESP flow has been modelled by means of mathematical modelling with various degrees of success world-wide. It was found that the accuracy of flow modelling as presently carried outby researchers world wide, is not sufficient to represent the complex inlet flow. Commercially available performance simulation software is based on empirical modelling principles and do not include the complexity of flow fields and re-entrainment and thus results have been limited in accuracy. Computational fluid dynamics software is commercially available and widely used to simulate industrial flow for plant design and optimisation. This technology has been applied with increasing confidence and success in the past. However, often the physical phenomena relevant for the performance simulation of the plant is not integrated into the code and specialised user routines are created to achieve a valid performance model. This research study introduces a unique integrated simulation methodology based on a commercial CFD code. The work focuses on the accurate modelling of fluid flow and collection dynamics in an ESP. User subroutines have been created to simulate particle charging, collection and re-entrainment. The results of the simulations are compared to measurement at actual plant.

Hydraulic energy absorbers may be described as high-loss centrifugal turbomachines arranged to operate as stalled torque converters. The device absorbs the kinetic energy of a vehicle in motion and dissipates the energy into water. A steady, single-phase, Computational Fluid Dynamics (CFD) simulation has been performed to investigate the flow field in a hydraulic energy absorber. It was determined that to better predict the performance of the energy absorber, more sophisticated modeling approaches may be needed. In this research, a steady, two-phase calculation with basic turbulence modeling was used as a first assessment. The two-phase model was used to investigate cavitation effects. Unsteady and advanced turbulence modeling techniques were then incorporated into single-phase calculations. The Multiple Reference Frame (MRF) Technique was used to model the interaction between the rotor and the stator. The calculations provided clearer details of the flow field without dramatically increasing the computational cost. It was found that unsteady modeling was necessary to correctly capture the close coupling between the rotor and the stator. The predicted torque in the unsteady calculations was 70% of the experimental value and twice of the result in the steady-state calculations. It was found that the inaccuracy of torque prediction was due to (1) high pressures in the regions with complicated geometrical boundaries and, (2) dynamic interactions between the rotor and the stator were not captured fully. It was also determined that the unrealistically low pressure values were not caused by the physical cavitation, but by the lack of proper boundary conditions for the model. Further integration of the modeling techniques studied would improve the CFD results for use in the design of the energy absorber. / Master of Science

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Approved for public release, distribution unlimited / As the United States Navy prepares to field a single engine jet, the F-35C Joint Strike Fighter, it is important that the causes of the .pop-stall. occurrence be understood. This problem arises as the jet engine ingests steam just prior to being released from the catapult. In examining this problem two Computational Fluid Dynamic (CFD) codes have been used by the Naval Postgraduate School to predict the performance of a transonic compressor rotor that is being tested with steam ingestion. Both codes, developed by NASA, provide a baseline that experimental results and new CFD codes can be compared with. Ansys Inc., a commercial Computer Aided Design (CAD) software company, has developed a new code that allows modeling of two phase flow. ICEM-CFD and CFX-5, both Anys Inc. programs that can model turbomachinery blade passages similar to that used by the NASA codes, were used in the present study. Comparisons were made with the experimental data and the predictions made by NASA codes as part of the initial modeling of the transonic compressor rotor flow field.

Approved for public release, distribution unlimited / As part of an initial baseline survey of the inlet flow-field into a transonic compressor rotor, a five-hole probe was calibrated and used to determine the Mach number and inlet pitch angle distributions. The data for Mach number were compared to data obtained with a three-hole probe. A numerical investigation of the flow in the inlet ducting to the rotor was also initiated using the commercial code CFX marketed by ANSYS. Comparisons were also made between the numerical predictions and the experimental measurements. The purpose of the study was to more accurately determine the characteristics of the flow to the rotor of the compressor prior to steam-ingestion experiments to quantify effects on compressor stability.

Approved for public release, distribution unlimited / The concept of a fan-wing aircraft configuration for the purpose of vertical takeoff and landing has drawn much attention. Recently, more investigations revealed that a cross-flow fan (CFF) was capable of providing the propulsion. Several characteristics of the off-design performance of a CFF were experimentally measured, but insufficient numerical predictions were obtained. In the present study, the commercial CFD software ANSYS CFX was employed to calculate the unsteady flow through a CFF with a sliding mesh incorporated. The results of the CFD showed the necessity to re-investigate the cross-flow fan with 12-inch diameter, 1/5-inch span and 30 blades, and additional measurement locations were implemented to carry out a more accurate experiment. A new digital sensor array was used to record the pressures within the experiment, which contributed to the high fidelity of the present data. Successful comparisons wre made between the predicted and measured performance at various rotational speeds from an open throttle position to a setting at stall. Visualization of the computed flow field showed where stall occurred, both within the rotor and in the exhaust duct.

Approved for public release, distribution unlimited / ry at simulated flight conditions, including supersonic cruising conditions. The spiral lines initiator demonstrated a lower total pressure loss with compared to the geometry with rings, and thus was the preferred initiator configuraiton. Experimental values for the turbulence were found to be significantly lower than the computed values at similar conditions when using the k-e model. Finally, successful ignitions of the JP-10/Air initiator at frequencies of up to 20 Hz were experimentally demonstrated. / Funded by: N0001406WR20161.