The initial rotation of flat, rectangular plates in quiescent flow were studied experimentally using two-dimensional and stereoscopic particle image velocimetry. The study examined the vortex dynamics of spanwise vorticity created on the upper, leeward surface of each plate of aspect ratio 2 and 4, which consists primarily of a leading-edge vortex. Reynolds numbers of 4,000, 8,000, and 16,000 based on the tip velocity and angles of attack of 25°, 35°, and 45° were investigated at five different azimuthal locations (90°, 180°, 235°, 270°, and 320°). The 25% and 50% spanwise positions for the aspect ratio 4 plate and 50% spanwise position for the aspect ratio 2 plate were studied. For the 25% and 50% spanwise location for the aspect ratio 4 and 2 plate, respectively, the leading-edge vortex structure's shape and coherence appear to be evolving temporally as the plate begins its initial motion. Leading-edge vortex circulation measurements confirm there is a non-monotonic trend showing increasing values until an azimuthal position of approximately 220° where there is a dip in the circulation values, but the circulation then rises towards the end of the range of azimuthal positions investigated. A strong region of counter-rotating vorticity was observed on the surface of the plate beneath the leading-edge vortex from the interaction of the leading-edge vortex with the plate. It was hypothesized that the interactions between the leading-edge vortex and counter-rotating vorticity are an important factor in governing the dynamics and strength of the leading-edge vortex which may ultimately determine whether the leading-edge vortex remains attached. To validate this claim, a transport analysis of the vorticity in the leading-edge vortex was developed to determine the contributions of spanwise flux, tilting of in-plane vorticity components, the shear layer, and annihilation has on the rate of change of circulation of the leading-edge vortex in the spanwise direction. Results of this analysis indicate that annihilation of the leading-edge vortex from entrainment of the counter-rotating vorticity is an important factor in governing the dynamics of the leading-edge vortex.

Internal crossflow is an important element to actual gas turbine blade cooling; however, there are very few studies in open literature that have documented its effects on turbine blade film cooling. Experiments measuring adiabatic effectiveness were conducted to investigate the effects of perpendicular crossflow on a row of 45 degree compound angle, cylindrical film cooling holes. Tests included a standard plenum condition, a baseline crossflow case consisting of a smooth-walled channel, and various crossflow configurations with ribs. The ribs were angled to the direction of prevailing internal crossflow at 45 and 135 degrees and were positioned at different locations. Experiments were conducted at a density ratio of DR=1.5 for a range of blowing ratios including M=0.5, 0.75, 1.0, 1.5, and 2.0. Results showed that internal crossflow can significantly influence adiabatic effectiveness when compared to the standard plenum condition. The implementation of ribs generally decreased the adiabatic effectiveness when compared to the smooth-walled crossflow case. The highest adiabatic effectiveness measurements were recorded for the smooth-walled case in which crossflow was directed against the spanwise hole orientation angle. Tests indicated that the direction of perpendicular crossflow in relation to the hole orientation can significantly influence the adiabatic effectiveness. Among the rib crossflow tests, rib configurations that directed the coolant forward in the direction of the mainstream resulted in higher adiabatic effectiveness measurements. However, no other parameters could consistently be identified correlating to increased film cooling performance. It is likely that a combination of factors are responsible for influencing performance, including internal local pressure caused by the ribs, the internal channel flow field, jet exit velocity profiles, and in-hole vortices. / text

The objective of this study was the development of a procedure in GT STRUDL to design reinforced concrete flat plate systems based on the results of finite element analysis. The current state-of-practice of reinforced concrete flat plate design was reviewed, including the ACI direct design and equivalent frame techniques, the yield line method, and the strip design method. The principles of these methods along with a critical evaluation of their applicability and limitations were presented as motivation for a finite element based design procedure. Additionally, the current state-of-the-art of flat plate design based on finite element results was presented, along with various flat plate modeling techniques. Design methodologies studied included the Wood and Armer approach, based on element stress resultants, and the resultant force approach, based on element forces. A flat plate design procedure based on the element force approach was embodied in the DESIGN SLAB command, which was implemented in GT STRUDL. The DESIGN SLAB command provides the user the ability to design a slab section by specifying a cut definition and several optional design parameters. The procedure determines all nodes and elements along the cut, computes the resultant moment design envelope acting on the cross-section, and designs the slab for flexure in accordance with provisions of ACI 318-02. Design examples presented include single-panel flat plate systems with various support conditions as well as multi-panel systems with regular and irregular column spacing. These examples allowed for critical comparison with results from experimental studies and currently applied design methods in order to determine the applicability of the implemented procedure. The DESIGN SLAB command was shown to produce design moments in agreement with experimental data as well as conventional design techniques for regular configurations. The examples additionally showed that when cuts were not oriented orthogonally to the directions of principle bending, resulting designs based on element forces could significantly under-reinforce the cross-section due to significant torsional effects.

Friction factor data are important for better prediction of leakage and rotordynamic coefficients of gas annular seals. A flat-plate test rig is used to determine friction factor of hole-pattern/honeycomb flat-plate surfaces representing annular seals. Three flat-plates, having a hole-pattern with hole diameter of 12.15 mm and hole depths of 0.9 mm, 1.9 mm, and 2.9 mm, are tested with air as the working medium. Air flow is produced between two surfaces, one having the hole-pattern roughness representing the hole-pattern seal and the other smooth, at the following three clearances of 0.254, 0.381, and 0.635 mm and three inlet pressures of 56, 70, and 84 bar with all possible pressure ratios at each configuration. The friction factor data are presented for all tested configurations, with description of the test rig and theory behind the calculations. The effect of hole diameter, hole depth, clearance, Reynolds number, and inlet pressure are analyzed, and friction factor models based on these parameters are calculated. Friction factor upset (an undesirable phenomenon making the test data non repeatable) is also explained. Dynamic pressure data are presented, measured from dynamic pressure probes located at both the hole-pattern plate and the smooth plates at different locations.

The current development of consumer electronics, driven by the effort to manufacture smaller products with increased performance, has amplified the chance for inducing higher thermal stresses to these systems. In an effort to devise more effective cooling methods for these systems, many scholars have studied the convective cooling of discrete heating elements. This report discusses a methodology for fabricating and testing a suitable flat plate design with discrete heating elements for both natural and forced convection cooling experiments. There were two plate design attempts: (i) an aluminum plate and (ii) a R3315 hydrostatic-resistance plastic foam plate. For the purpose of conducting experiments for the discrete heating elements, the foam plate design was found to be an appropriate design. After designing a proper foam plate, several experiments were conducted for the natural convection case. The combination of parameters such as the geometric location and power output ratio between heaters that resulted in the maximum thermal conductance were studied. / text

The nonlinear transition regime of supersonic boundary layers at low to moderate supersonic Mach numbers (Mach 2-3:5) under wind-tunnel conditions is studied using linear stability theory (LST) and direct numerical simulations (DNS). Two main flow configurations are chosen, a flat-plate boundary layer and a cone boundary layer. Previous investigations of the early nonlinear transition regime have mainly focused on two nonlinear mechanisms, the so-called "oblique breakdown" mechanism and "asymmetric subharmonic resonance". The first mechanism has only been investigated numerically while the second mechanism was first observed in experiments. This dissertation discusses three open questions related to both mechanisms: (i) Can oblique breakdown be identified in old wind-tunnel experiments published in the literature, (ii) what is the most dominant breakdown mechanism for a supersonic boundary layer, oblique breakdown or asymmetric subharmonic resonance, and (iii) does oblique breakdown lead to a fully developed turbulent boundary layer? By adopting the flow conditions and the disturbance generation of a specific experiment from the literature, in which asymmetric subharmonic resonance in a wave train was studied, it was possible to show that oblique breakdown might also have been present in the experiment, although oblique breakdown was not reported by the experimentalists. Hence, this experiment might provide the first experimental evidence of oblique breakdown for a supersonic boundary layer. The second question was addressed by performing DNS of a wave packet. A wave packet is typically used as a model of a broadband disturbance environment. If a nonlinear mechanism is dominant, it should leave strong imprints in the disturbance spectrum of the wave packet. In the DNS of the wave packet, oblique breakdown was visible in the disturbance spectrum while subharmonic resonance played only a minor role. To study the last question, a set of DNS of the entire transition path from the linear regime to the turbulence stage was conducted. Some of these simulations demonstrated that the ow reached turbulence near the downstream end of the computational domain.

No description available.

abstract: Tesla turbo-machinery offers a robust, easily manufactured, extremely versatile prime mover with inherent capabilities making it perhaps the best, if not the only, solution for certain niche applications. The goal of this thesis is not to optimize the performance of the Tesla turbine, but to compare its performance with various working fluids. Theoretical and experimental analyses of a turbine-generator assembly utilizing compressed air, saturated steam and water as the working fluids were performed and are presented in this work. A brief background and explanation of the technology is provided along with potential applications. A theoretical thermodynamic analysis is outlined, resulting in turbine and rotor efficiencies, power outputs and Reynolds numbers calculated for the turbine for various combinations of working fluids and inlet nozzles. The results indicate the turbine is capable of achieving a turbine efficiency of 31.17 ± 3.61% and an estimated rotor efficiency 95 ± 9.32%. These efficiencies are promising considering the numerous losses still present in the current design. Calculation of the Reynolds number provided some capability to determine the flow behavior and how that behavior impacts the performance and efficiency of the Tesla turbine. It was determined that turbulence in the flow is essential to achieving high power outputs and high efficiency. Although the efficiency, after peaking, begins to slightly taper off as the flow becomes increasingly turbulent, the power output maintains a steady linear increase. / Dissertation/Thesis / M.S. Mechanical Engineering 2012

Thermoelectric generator (TEG) is a solid state technology based on the Seebeck effect that can generate electrical power from waste heat. For continuous electrical power generation heat exchangers are integrated into the “cold side” and the “hot side” of the TEG such that a temperature difference across the TEG can be established and maintained. This thesis will focus on characterizing two different flat-plate cold side heat exchanger prototypes specifically designed for dissipating the thermal loads from TEG modules. The majority of TEGs modules available have a flat geometry design and a square shape with typical dimension of 40 mm × 40 mm or 56 mm × 56 mm. To maximize the net electrical power generated by the TEGs the cold side heat exchanger is required to have uniform surface temperature distribution, and excellent heat transfer performance with minimum pressure drop. To achieve the previously mentioned requirements, two flat-plate heat exchanger prototypes having two distinct heat transfer techniques were investigated. Each heat exchanger is designed to accommodate an array of 14 TEG modules arranged in two parallel rows with 7 TEGs per row a typical arrangement for large waste energy harvesting applications. The first heat exchanger prototype utilized single-phase forced convection through 140 minichannels (1 mm × 1 mm × 90 mm long) as a heat transfer technique. The second prototype utilized 14 liquid jets, 3 mm in diameter and 40.3 mm apart, impinging on a flat surface located 5 mm above. Each impinging jets was positioned at the centre of the TEG cooling area. An experimental facility was constructed in order to test the minichannels heat exchanger and the impinging jets thermally and hydrodynamically. The heat transfer, pressure drop and temperature distribution results were compared to determine the most appropriate cold side heat exchanger prototype for the TEG POWER system. The TEG POWER system is a waste heat recovery system designed to recoup waste heat from the exhaust gases of commercial pizza ovens. The TEG POWER system is capable of harvesting waste thermal energy produced by an establishment and utilize it for electrical power generation and thermal storage purposes. Heat transfer results indicated that for a given mass flow rate the minichannels heat exchanger has better heat transfer performance compared to the impinging jets heat exchanger. The minichannels heat exchanger design had a thermal conductance of 238 W/C at 0.19 kg/s coolant flow rate compared to 111 W/C for the impinging jets heat exchanger. The total pressure drop and the minor losses for each heat exchanger prototype were measured experimentally. For the minichannels heat exchanger, the total pressure drop is 23.3 kPa at flow rate of 0.235 kg/s. Comparatively, the total pressure drop for the impinging jets heat exchanger was 27.4 kPa at the same flow rate. Fittings losses for the minichannels heat and impinging jets heat exchanger were found to be 50% and 80% respectively. The maximum total measured drop corresponded to pumping power requirements of 5.7 W and 6.8 W for the minichannels and impinging jets heat exchanger respectively. Local and average temperature distributions and their influence on the electrical power generated were studied for both heat exchanger prototypes. It was found that the minichannels heat exchanger offers more uniform surface temperature distribution per row of TEGs compared to the impinging jets heat exchanger. Therefore the minichannels heat exchanger is well suited for cooling two rows of TEGs simultaneously. Based on the thermal and hydrodynamics comparison results the minichannels heat exchanger prototype is recommended for implementation in the TEG POWER system. / Thesis / Master of Applied Science (MASc)

Wind energy is identified a promising energy resource in Sri Lanka. Therefore, it is important to use proper technologies for efficient energy capturing in order to minimize cost of energy. Small scale wind turbines are usually installed in constricted places (particularly in urban areas) where wind flow is turbulent and difficult to predict. Savonious type vertical axis wind turbines are important due to several reasons such as good response to turbulent winds, high initial torque, low cost, low noise, less maintenance.In this study, a modified flat plate type Savonius wind rotor was proposed to cost effectively harness wind energy in constricted places. Generally, vertical axis wind turbines (VAWT) are less efficient than horizontal axis wind turbines, one reason behind this issue is wind force difference between the 2 sides of the axis is small and due to this reason torque is small and power generation capacity is less.A prototype of the proposed VAWT was fabricated and the performance was determined by acquiring experimental data. Artificial wind blow which was generated by a huge fan was used to measure rotational speed and torque characteristics at varying wind speeds. Data were collected with 1-second sampling time and a data acquisition system was developed under this study. In the proposed design one side of the turbine blades are facing the wind direction in order to capture maximum force while other side is edging the blades to have minimum opposite torque. With this concept it is expected to maximize the torque of the axis and generate more power. A sort of a passive pitch mechanism is therefore utilized in order to save energy and simplify the system. Turbine blades are simple flat plates and it eliminates usage of complex aero foils. Due to the simplicity of this design it would be possible to use this turbine for domestic electricity generation at affordable costs.Nowadays, net metering systems are being promoted in Sri Lanka and it would be beneficial to introduce low cost VAWT which operates at low winds as well as turbulent wind conditions. Based on typical household hourly load profile, viability of proposed vertical axis wind turbine was evaluated by considering rural and urban wind regimes in Sri Lanka. The costs of wind energy at two selected locations were determined in the context of net metering.