A computational study was conducted on the flow, both compressible and incompressible, in a labyrinth seal at various geometries and rotation rates. The computations were performed using the commercial software Fluent® which solves the k-ε model to predict the flow field in the seal. Various clearance-pitch ratios were used to study the effect of clearance on the flow. The aspect ratio, which is defined as the pitch-height ratio was varied to study the influence of the depth of the cavity on the flow as a whole. These studies span a range of Taylor's number that is defined accordingly, while fixing the Reynolds number at 1000. The effects of clearance, aspect ratio and rotational rates are studied using carry-over coefficient and discharge coefficient. It is observed that a secondary recirculation zone (SRZ) occurs inside a seal cavity at above certain Taylor's number. This significantly changes the flow field in the seal and the cavity which results an increases in pressure drop across the seal for a given flow boundary condition. This formation of SRZ's is more evident in incompressible flow and occur at prohibitively high rotational speeds in case of air (compressible flow). It is also observed that flow with teeth on rotor are characterized by SRZ's while it's not case with teeth on stator. A flow map which shows the onset and presence of SRZ's is shown. The ratio of tangential velocity of the shaft to the average of the swirl velocity in a cavity at various geometries of the cavities are presented. They seem to be decreasing with decreasing depth and follow a linear pattern with the aspect ratios of the cavity.

Rotordynamic instability problems in turbomachinery have become more important in recent years due to rotordynamic components with higher speeds and higher power densities. These features typically lead to increased instability risk in rotor dynamic components as fluids-structure interactions take place. In addition, critical damage of rotordynamic components can result from high level vibrations of supporting bearing system, where the reduced rotor speed can lead to system operating near the rotor critical speed. Therefore, increased accuracy in modeling of rotordynamic components is required to predict the potential instability issues in high performance rotordynamic design. The instability issue may potentially be eliminated in design stage by varying the characteristics of the unstable components. One such turbomachinery component is the annular pressure seal. The annular pressure seals are specifically designed to prevent the fluid leakage from high pressure stage to low pressure stage in turbomachinery. Typical annular pressure seals have two different flow regions, an annular jet-flow region between the rotor and stator, and cylindrical or circumferential indentions on the stator/rotor surface that serve as cavities where flow recirculation occurs. As the working fluid enters the cavities and recirculates, the kinetic energy is reduced, resulting in a reduction of leakage flow. The current challenge is to model with higher precision the interaction between the rotordynamic components and the working fluid. In this dissertation, this challenge was overcome by developing a hybrid Bulk Flow/CFD method to compute rotordynamic responses for the annular pressure seals. In addition, design of experiments studies were performed to relate the surface patterning with the resulting rotordynamic response for the annular pressure seals, in which several different geometry specifications were investigated. This study on annular pressure seal design generated regression models for rotordynamic coefficients that can be used as optimization guidelines. Research topics related to the annular pressure seals were presented in this dissertation as well. The reduced order model of both hole-pattern seals and labyrinth seals were investigated. The results showed that the flow field representing the flow dynamics in annular pressure seals can be expressed as a combination of first three proper orthogonal decomposition modes. In addition, supercritical state of carbon dioxide (sCO2) process fluid was examined as the working fluid in a preliminary study to better understand the effects on annular pressure seals. The results showed that the performance and stability in the annular pressure seals using sCO2 as process fluid can both be improved. / Doctor of Philosophy / This dissertation focused on understanding the correlations between surface patterning and rotordynamic responses in the annular pressure seals. The annular pressure seals are a specific type of rotordynamic component that was designed to prevent the fluid leakage from high pressure stage to low pressure stage in turbomachinery. As the working fluid enters the cavities and recirculates, the kinetic energy is reduced, resulting in a reduction of leakage flow through the annular pressure seals. Rotordynamic instability becomes an issue that may be related to the annular pressure seals in some cases. In recent years, rotordynamic components with higher rotor speeds and higher power densities are commonly used in industrial applications. These features could lead to increased instability risk in rotor-bearing systems as fluids-structure interactions take place. Therefore, high precision modeling of the rotodynamic components is required to predict the instability issues in high performance rotordynamic design. The instability issue may potentially be eliminated in design stage by varying the characteristics of the potentially unstable components. In this study, the surface patterning and rotordynamic responses were investigated for several different annular pressure seal models with a hybrid Bulk Flow/Computational Fluid Dynamics method. This dissertation provides for the first time regression models for rotordynamic coefficients that can be used as optimization guidelines. Research topics related to the annular pressure seals were presented in this dissertation as well. The reduced order model of both hole-pattern seals and labyrinth seals were investigated. The results showed that the flow field representing the flow dynamics in annular pressure seals can be expressed as a combination of first three proper orthogonal decomposition modes. In addition, supercritical state of carbon dioxide (sCO2) process fluid was examined to better understand the effects of working fluid on annular pressure seals. The results showed that the performance and stability in the annular pressure seals using sCO2 as process fluid can both be improved.

This diploma thesis deals with the repair of a steam backpressure single-stage turbine. This thesis is assigned to a specific Spilling turbine case. A revisional report of this turbine with repair or exchange suggestions of demaged turbine parts is processed. In addition, a simulation of the contact pressure is carried out on the split plane of the housing. Structural modifications are designed and simulated to increase the parting plane's tightness. Further, the calculation of the tightening torque of the split plane is performed and a control thermodynamic and strength calculation of the labyrinth seals is performed.

The goal of this Master’s thesis is to create the design of a low power condensing steam turbine. The turbine has a Curtis control stage and a reaction blading. The work also contains the calculation of gland labyrinth seals and the balancing piston, specification of a forces and losses at bearings. Finally, the gearbox and generator are selected and the efficiency at generator’s clamps is specified. The Master’s thesis includes the design drawing of a longitudinal turbine view.

The ability to quantify leakage flow and windage heating for labyrinth seals with honeycomb lands is critical in understanding gas turbine engine system performance and predicting its component lifes. Variety of labyrinth seal configurations (number of teeth, stepped or straight, honeycomb cell size) are in use in gas turbines, and for each configuration, there are many additional geometric factors that can impact a seal’s leakage and windage characteristics. To achieve high performance in modern gas turbine engines, the labyrinth seals operate at low clearances and high rotational speed which are generally deployed with honeycomb lands on the stator. During the transient operation of aircraft engines, the stator and rotor mechanical and thermal growths differ from one another and can often result in the rotor’s incursion into the stator honeycomb structure. The incursions create rub-grooves in the honeycomb lands that can subsequently enlarge as the engine undergoes various manoeuvres. However, the effects of different honeycomb cell size, rotation and presence of rub-groove have not been thoroughly investigated in previously published work. The objective of the present research is to numerically investigate the influence of the above three factors on seal leakage and windage heating. The present work focuses the development of a numerical methodology aimed at studying above effects. Specifically, a three-dimensional CFD model is developed utilizing commercial finite volume-based software incorporating the RNG k-ε turbulence model. Detail validation of the numerical model is performed by comparing the leakage and windage heating measurements of several rig tests. The turbulent Schmidt number is found to be an important parameter governing the leakage prediction. It depends on honeycomb cell size and clearance for honeycomb seals, and Reynolds number in the presence smooth lands. The present numerical model with the modified RNG k- turbulence model predicts seal leakage and windage heating within 3-10% with available experimental data. Using the validated numerical model, a broad parametric study is conducted by varying honeycomb cell size, radial clearance, pressure ratio and rotational speed for a four-tooth straight-through labyrinth seal with and without rub-grooves. They further indicate that presence of rub-grooves increases seal leakage and reduce windage heating, specifically at smaller clearance and for larger honeycomb cell size. Rotation significantly reduces leakage with smooth stator land and smaller honeycomb cells whereas the effect is minimal for larger (3.2mm) honeycomb cells. However, at very high rotational speed seal flow reduces in all seal configurations due to high temperature rise and Rayleigh line effects. At no rub condition and lower clearance, the larger honeycomb cells leak more flow due to high bypass flow through the honeycomb cells. This results into lower pocket swirl and higher windage. When the seal clearance increases the larger honeycomb cells offers more drag to the seal flow, therefore they leak less. At higher clearances the flow travels like a strong wall jet and isolates the pocket air from honeycomb cells. Hence, at open clearances labyrinth seals with any honeycomb cell size essentially produce the same pocket swirl and windage heating.