An experimental study was performed to investigate the mechanics of fluid flow in a 30<SUP>o</SUP> annular diffuser, and to study the periodicity of flow oscillations in this region. Surface oil-flow patterns and smoke-flow visualisation experiments were performed with a centrebody concentric and eccentric in the diffuser. Above a threshold offset, the measurements revealed two contra-rotating periodic vortices in antiphase with each other, symmetrically disposed about the plane of minimum clearance in the annulus, and originating in the 30<SUP>o</SUP> diffuser. Steady pressure measurements indicated that the steady fluid forces acting on the centre body are decentralising, and any small perturbation will result in the centrebody being pushed towards the wall of the diffuser. Unsteady pressure and force measurements showed that for a mean eccentric centrebody position, there was a predominantly tangential unsteady vortex force present with the centre body both fixed and vibrating. This vortex force scaled linearly with flow velocity, indicating a Strouhal-type mechanism. The magnitude of the vortex force was independent of both amplitude and frequency of vibration of the centrebody, indicating a forced vibration effect. The exception was when the centre body frequency approached the vortex shedding frequency, in which case lock-on occurred. For the geometry considered, lock-on does <i>not</i> significantly increase the unsteady forces acting on the centrebody. During lock-on it was found that the vortices could not only be influenced by centrebody motion, but could be completely suppressed by closely controlling the amplitude and frequency of the centrebody. The effect that shaking the centrebody has on the different flow regimes in which the annular diffuser operates is explained. The vortices could also be eliminted by a) attaching a small helical fence to the surface of the centrebody, and b) by inserting a perforated liner within, and downstream of, the diffuser section. A small perturbation theoretical analysis of the unsteady flow in the diffuser has been developed. The flow was computed numerically, and the predicted self-induced forces examined. The analysis predicted mainly negative damping for the configurations examined. The predicted magnitude of the unsteady forces agreed with experimental results. Finally, the flow was also predicted analytically, and a good level of agreement with the numerical study was found.

No description available.

Instantaneous wall-pressure data were recorded for a 25% eccentric whirling annular seal for rotor speeds of 1800RPM and 3600RPM, axial Reynolds numbers of 24000 and 12000, and whirl ratios of 0.1-1.0 following the procedure set forth by Winslow (1994), Robic (1999) and Suryanarayanan (2003). Overall, the phase averaged wall-pressure distributions were consistent with previous results. The “switch” in the pressure distribution measured by Suryanarayanan (2003) and Robic (1999) from pressure to suction between the seal entrance and exit occurs at and above a whirl ratio of 0.7 for 1800RPM and 0.4 for 3600RPM. For both rotor speeds, decreasing the flow rate by one-half also decreases the wall pressure fluctuation distributions by one-half. For whirl ratios less than 0.5, the phase averaged pressure field was relatively constant which leads to minimal forces being imparted on the rotor by the fluid in the annulus. Talyor-Gortler vortices are measured for 1800RPM and Re=24000 at whirl ratios 0.1 and 0.3-0.7. As the whirl ratio increases past 0.5, longitudinal vortices begin to emerge in the pressure contours and skew axially with 180° shifts occurring when the Taylor-Reynolds ratio is large enough. Longitudinal vortices were measured for both rotor speeds when the whirling motion is greater than 1400RPM for Re=12000 and greater than 1600RPM for Re=24000. Attempts were made to apply Childs (1983) procedure for finding the rotordynamic coefficients of annular seals; however, the seal moves in a non-circular orbit about the seal’s center so Childs analysis cannot be applied.

In any rotating machinery, the geometry of the seal influences the extent of systemleakage. The path taken by the flow in the clearance volume is dependent on the seal and rotor profile. The clearance between a new "seal-rotor" combination is uniform except for small variations during manufacturing and assembly. With time this annular cross section undergoes further physical changes causing non-uniform flow in the annular volume. This azimuthally varying leakage through the seal-rotor annulus creates unbalanced forces on the rotor causing it to whirl. It is essential to identify the reasons for these unwanted forces. Velocity profiling of the clearance volume flow was performed by Morrison et al. (1992) using 3-D LDA measurements on annular and labyrinth seals operating with 50% dynamic eccentricities and a whirl ratio of one. However, this alone does not provide a complete matrix of data for the conditions prevailing in the clearance zone. Additional information of mean and instantaneous wall pressure distributions for 0%, 10%, 25% and 50% rotor dynamic eccentricity for whirl ratios of zero and one, with positive pre-swirl, no pre-swirl and negative pre-swirl conditions were measured by Robic (1999). The data collected showed that the pressure field on the seal walls reversed itself between the whirling and non-whirling conditions. As a continuance of the earlier works, the present effort investigates the effect of whirl ratio variation for a 50% eccentric smooth annular seal at a leakage Reynolds number of 24000. An attempt has been made to collect pressure data for negative whirl ratios also under similar test conditions. A seal test rig capable of handling different eccentricities and whirl ratios simultaneously was designed and constructed for this purpose. Mean and instantaneous wall pressure data were recorded for 50% eccentricity with whirl ratios between ? 1 for a rotor speed of 1800. For a rotor speed of 2700, whirl ratios tested were between ? 0.6 and for 3600 rotor speed, whirl ratios ranging between ? 0.5 were tested. From the collected data a detailed analysis of wall pressures along the seal surface is performed following the technique described by Winslow (1994) and Robic (1999).

Instantaneous wall-pressure data were recorded for a 25% eccentric whirling annular seal for rotor speeds of 1800RPM and 3600RPM, axial Reynolds numbers of 24000 and 12000, and whirl ratios of 0.1-1.0 following the procedure set forth by Winslow (1994), Robic (1999) and Suryanarayanan (2003). Overall, the phase averaged wall-pressure distributions were consistent with previous results. The “switch” in the pressure distribution measured by Suryanarayanan (2003) and Robic (1999) from pressure to suction between the seal entrance and exit occurs at and above a whirl ratio of 0.7 for 1800RPM and 0.4 for 3600RPM. For both rotor speeds, decreasing the flow rate by one-half also decreases the wall pressure fluctuation distributions by one-half. For whirl ratios less than 0.5, the phase averaged pressure field was relatively constant which leads to minimal forces being imparted on the rotor by the fluid in the annulus. Talyor-Gortler vortices are measured for 1800RPM and Re=24000 at whirl ratios 0.1 and 0.3-0.7. As the whirl ratio increases past 0.5, longitudinal vortices begin to emerge in the pressure contours and skew axially with 180° shifts occurring when the Taylor-Reynolds ratio is large enough. Longitudinal vortices were measured for both rotor speeds when the whirling motion is greater than 1400RPM for Re=12000 and greater than 1600RPM for Re=24000. Attempts were made to apply Childs (1983) procedure for finding the rotordynamic coefficients of annular seals; however, the seal moves in a non-circular orbit about the seal’s center so Childs analysis cannot be applied.

No description available.

The goal of this project is to develop a fabrication process for an annular thermoelectric module using a powder methodology that can potentially later be automated for high volume manufacturing. Prototypes were produced and experimentally tested to study and characterize thermal and effective Seebeck performance. Manufacturing procedure parameters were changed systematically to characterize the impact on key performance parameters and develop the fabrication process. Parameters investigated were sintering temperature, pressing pressure, oxide reduction and geometry. A novel design for an annular thermoelectric generator geometry has been proposed. The new geometry utilizes more of the module material into power production making the geometry more efficient than the typical ring-structured modules similar to that proposed by Min & Rowe (2007). Experimental results tests highlighting only geometry differences showed V-shaped modules with higher effective Seebeck coefficient compared to ring-structured modules. Experimental results showed the proposed V-shaped annular thermoelectric generator prototype with a Seebeck coefficient of 190.75 µV/K compared to (Min & Rowe, 2007)’s earlier ring-structured prototype measuring a Seebeck coefficient of 145 µV/K. A numerical simulation model was created to compare electrical and thermal behaviour for different TEG module geometries. ANSYS Workbench® simulation results show that V-shaped TEG module outperforms the ring-structured design similar to Min et al.’s design by 7% to 9% under different conditions. / Thesis / Master of Science in Mechanical Engineering (MSME)

No description available.

Annular seals are devices, which are used in turboMachinery systems to reduce the flow leakage, and to provide better dynamic stability to the system. Leakage flow can strongly affect cooling quality, heating balance, and efficiency of a turboMachinery system. Due to the fact that annular seals can significantly reduce the flow leakage, and provide the most cost-effective way of enhancing the aerodynamic efficiency, understanding of the flow characteristics through the annular seal configurations is an important subject. Seals are classified in two main groups, which are contacting, and non-contacting seals. Straight annular and convergent seal configurations are characterized as non-contacting seals, and they are widely used in rotating turbocMachinery systems. The flow kinetic energy obtained from the flow pressure is dissipated by the effects of shear stresses along the free shear layers. In addition, viscosity of the flow has an impact on the dissipation rate of the flow kinetic energy. In this research, the leakage characteristics of the straight annular, and convergent seal configurations under specified working conditions are compared to each other. This study aims to investigate which seal configuration exhibits better leakage characteristics with respect to the different seal clearances, shaft speeds, surface roughness heights, and pressure ratios. Commercial code ANSYS Fluent is used to perform the flow simulations for the straight annular and convergent seal configurations. Effects of the seal clearances, shaft speeds, pressure ratios, and surface roughness heights on the leakage rate are analyzed. It was observed that the seal clearance has a significant impact on the flow leakage, and clearance control is an important subject in seal technology. Additionally, dynamic system is compared to the static system, and results showed that shaft speed less than 15,000 rpm has not considerable impacts on the leakage.

With the continued economic and socio-political pressure on aircraft manufacturers to produce more profitable and environmentally-friendly aircraft, the drive towards increasingly more efficient aircraft engines remains of prime importance to aircraft engine manufacturers. While the majority of axial flow turbomachines use cylindrically shaped endwalls between the blades on the hub or shroud, non-axisymmetric endwall contouring is a reasonably recent technique which relaxes this constraint, and allows the geometry of the endwalls to depart from that of a plain cylinder. Although a number of studies have shown non-axisymmetric endwall contouring to be an effective mechanism for the reduction of secondary flows (and the losses associated with them), within the open literature there still remains a general lack of detailed information relating to the optimal design of these devices. Among some of the most important issues which remain unresolved, are uncertainties such as: “What is the best way to identify and thereafter quantify the strength of turbine secondary flows?”, and thereafter, as a natural progression from this, “Of the metrics which are currently found within the literature, which are best for use in the design of secondary loss mitigating endwall contours for a real turbine?”. Some of the reasons for the lack of information as described above, result from the undertaking of many of the investigations into the design of endwall contours by or on behalf of the major engine manufacturers, and therefore, a general inability or perhaps even unwillingness to divulge many of the specific details related to the methodologies and quantities used as a result of the commercial sensitivity of these investigations. In addition to this, as a result of the relatively large number and diverse nature of groups involved in non-axisymmetric endwall contouring research, within the literature which has been made available, there exists a wide variety of different test geometries as well as conditions which have been used, making a neutral determination of the most successful approach to endwall contouring considerably more difficult. This thesis documents the design and testing of a number of different non-axisymmetric endwall configurations intended to produce flow conditions optimized using a selection of the metrics commonly found in the literature, for the rotor of a low speed, research turbine, whose baseline as well as performance using contoured endwalls has been reported on previously, in order to establish which of these metrics is the most effective. As part of this process, a fully validated computational fluid dynamics model of the turbine downstream of the first nozzle was developed and incorporated into an automated non-axisymmetric end- wall design routine, capable of producing endwall contours optimized for various objective functions. Numerical testing showed that, in order to distinguish accurately between the various endwall configurations, relatively fine computational meshes were required and therefore, as a result of corresponding computational expense associated with these meshes, the implementation of a surrogate modelling procedure in which part of this computational cost is offset by mathematical modelling, was necessary. Altogether, a total of 8 endwall designs were produced - 6 using a single metric each as the basis of their objective functions (the ‘simple’ designs) and a further 2 so-called ‘compound’ designs. Of the simple designs, the best performing endwalls in terms of improvements to the rotor exit efficiency were the ηtt-, Cske- &amp; βdev-based designs, which were based in turn on the rotor total-total efficiency (ηtt), coefficient of secondary kinetic energy (Cske) and flow deviation from design angle (βdev) respectively. All three of these designs were predicted to result in very similar changes to the secondary flow characteristics although the increasing bias towards flow correction was found to have an inverse correlation with the overall efficiencies predicted for each rotor. Of these designs, the numerical predictions for both the ηtt- &amp; Cske-based designs (which were included in the experimental subset), were found to be validated, at both the rotor exit as well as downstream measurement planes. Further to this (with the exception of the Cp0,rel-based case), although the remainder of the simple designs (i.e. the SKEH &amp; ηde-based designs) were also predicted to improve the overall rotor efficiency, either the form or the performance of these endwalls resulted in the final corresponding designs for these metrics being considered unsatisfactory. Finally, the two ‘compound’ metrics were both formulated to to include a term designed to target the secondary flow within the target blade row, as well as an additional term which was designed to promote improvement in the flow into the downstream blade row. While both designs produced using the compound design objective functions were predicted to improve both the conditions for the target blade row, as well as the flow quality at the exit of the blade row, flow separations at the exit of the contoured regions for both designs resulted in only partial validation of each design when tested experimentally. Finally, although both designs were once again predicted to perform very well at the ‘mixed-out’ measurement plane, these predictions were found to be only partially validated by the experiment.