abstract: Modern gas turbines operate at high mainstream gas temperatures and pressures, which requires high durability materials. A method of preventing these hot gases from leaking into the turbine cavities is essential for improved reliability and cost reduction. Utilizing bleed-off air from the compressor to cool internal components has been a common solution, but at the cost of decreasing turbine performance. The present work thoroughly describes the complex flow field between the mainstream gas and a single rotor-stator disk cavity, and mechanisms of mainstream gas ingestion. A combined approach of experimental measurement and numerical simulation are performed on the flow in a single-stage model gas turbine. Mainstream gas ingestion into the cavity is further reduced by utilizing two axially overlapping seal rings, one on the rotor disk and the other on the stator wall. Secondary purge air is injected into the rotor-stator cavity pre-swirled through the stator radially inboard of the two seal rings. Flow field predictions from the simulations are compared against experimental measurements of static pressure, velocity, and tracer gas concentration acquired in a nearly identical model configuration. Operational conditions were performed with a main airflow Reynolds number of 7.86e4 and a rotor disk speed of 3000rpm. Additionally the rotational Reynolds number was 8.74e5 with a purge air nondimensional flow rate cw=4806. The simulation models a 1/14 rotationally periodic sector of the turbine rig, consisting of four rotor blades and four stator vanes. Gambit was used to generate the three-dimensional unstructured grids ranging from 10 to 20 million cells. Effects of turbulence were modeled using the single-equation Spalart-Allmaras as well as the realizable k-epsilon models. Computations were performed using FLUENT for both a simplified steady-state and subsequent time-dependent formulation. Simulation results show larger scale structures across the entire sector angle inside the cavity and certain unsteady mainstream ingestion mechanisms are realized from the tracer gas. Simulated velocity distributions were scrutinized against Particle Image Velocimetry plots in the rotor-stator cavity and are in reasonable agreement with all of the measurements. / Dissertation/Thesis / M.S. Engineering 2010

Internal Combustion Engine (ICE) exhaust components are exposed to extreme operating temperatures. Thus, it is necessary that they are designed with materials that can sustain thermal and vibrational stresses. This study investigates the wear mechanisms and tribological performance of the exhaust manifold joint in Scania CV diesel trucks, focusing on the lip seal ring between the exhaust and turbo manifolds. The joint is prone to wear due to thermal and vibrational stresses, impacting its service life and raising environmental concerns. The manifold material, ductile cast iron SiMo51, offers good thermal resistance, while the lip seal ring, made of Inconel 718c, provides excellent thermal fatigue and corrosion resistance, coated with AlTiN for wear and oxidation resistance. However, the tribological performance of this joint and material combination remains unknown, necessitating further research.  This work aims to understand wear initiation mechanisms and their relationship with temperature. Test setups were established using an oscillating cylinder on disc configuration in the SRV 3 tribometer. SiMo51 uncoated/coated with Tribaloy 400 and Inconel 718c uncoated/coated with AlTiN were tested against each other to identify the best material pair. Analysis involved coefficient of friction, visual inspection, wear volume measurements, SEM micrographs, and EDS for surface chemical composition. Results indicated that friction behaviour is temperature-dependent, with oxide layer formation reducing the coefficient of friction when the manifold is uncoated, while the opposite occurs when coated with Tribaloy 400. Wear behaviour varied based on material combinations and temperature. Uncoated manifold exhibited dominant adhesion (galling) accompanied by tribo-oxidation at higher temperatures, with maximum wear volumes at room temperature. Introduction of T-400 on the manifold initiated galling on the lip seal, leading to abrasion on the manifold surface, accompanied by tribo-oxidation at elevated temperatures. Wear increased until 500°C, followed by a decrease at 700°C. Further explanations of T-400 wear behaviour are lacking in the literature.