Gas Turbine Engines operate at temperatures higher than current material temperature limits. This necessitates cooling the metal through internal or external means and/ or protecting the metal with coatings that have higher material limits. Film cooling is one of the major technologies allowing today’s gas turbines to operate at extremely high turbine inlet temperatures, consequently higher power density, and extend the cooled components life. Film cooling is a technique where a coolant is blown over the surface exposed to hot gas and a film of low temperature gas is maintained that protects the metal surface from the hot gas. The application of effective film-cooling techniques provides the first and best line of defense for hot gas path surfaces against the onslaught of extreme heat fluxes, serving to directly reduce the incident convective heat flux on the surface. The effectiveness of film cooling methods depends on the blowing ratio, shape of the cooling holes, and geometrical parameters such as the area ratio and diffusion angle. Film cooling is performed almost exclusively through the use of discrete holes. The holes can be of round or other shaped. A detailed study of the literature shows that the fan shaped has higher effectiveness when compared to other shapes. In this study a number of cooling hole shapes are evaluated numerically using the Computational Fluid Dynamics (CFD) tool ANSYS-CFX-11.0 with the objective of improving cooling effectiveness under a favorable pressure gradient main flow. In order to delineate the effects of shape from that of diffusion, a constant area ratio is assumed first. In the next set of analyses the effect of hole exit diffusion is considered. Results are presented in terms of surface temperatures and adiabatic effectiveness at three different blowing ratios for the different film cooling hole shapes analyzed. Comparison is made with reference to the fan shaped film cooling hole with forward and lateral angles of 10/10/10 degree respectively. Hole shapes that show improvement over the fan shaped hole are identified and optimized.

HP turbine cooling systems utilize a TOBI (tangential on-board injector) nozzle and seal-plate to deliver cooling air to the airfoils with minimal loss in pressure and a benefit in relative total temperature. It was necessary to have a low TOBI exit pressure to control excess leakage across adjacent labyrinth seals with a trade-off of maintaining adequate pressure to supply blade cooling. Consequently, pumping vanes were needed on the seal-plate to restore pressure, which adds parasitic work to the turbine and a corresponding loss of engine efficiency. Engine testing revealed recirculation zones attached to the radial pumping vanes. Subsequent numerical simulation corroborated the recirculation and resulting circumferential asymmetry in flow distribution to the cooled airfoils. As a consequence, excess cooling air is supplied to the HP rotor with some airfoils receiving the minimum amount of cooling air. This study seeks to improve the flow distribution and pumping effectiveness by means of contouring the pumping vanes, increasing pumping vane solidity and/or controlling diffusion by re-contouring the seal-plate surface. Design features that increase total through flow when overall pressure ratio is fixed are also explored.

Design improvements on labyrinth seal teeth and a honeycomb land are examined by three-dimensional CFD numerical modeling of the flow field. The only objective is reduction of the total leakage through the new seal. CFD assumptions and analysis was validated by comparison with leakage data from labyrinth seal experiments conducted by Stocker [1]. The baseline chosen for comparison of sealing effectiveness is a conventional low clearance straight-through labyrinth seal with four teeth and a honeycomb land of symmetrical hexagonal cells. The proposed new seal has a staggered honeycomb land and straight teeth with an inclined notch. CFD predicts ∼17% reduction in seal leakage at a radial clearance of 0.005 inch (0.122mm) due to higher wall friction and flow turbulence.

The flow discharge through thick orifices with approaching flow normal and inclined to the orifice axis was numerically predicted. The objective is to validate Fluent code predictions of discharge coefficient against Rohde et al. experimental data and arrive at an optimum mesh in terms of effort, simulation time and accuracy. CFD simulations were performed on several Rohde et al. experimental models with orifice thickness to length ratio varying from 0.5 to 4.0, with sharp and rounded inlet edges and orifice axis inclined 45 degrees to the approaching flow. The approach Mach number varies from 0.07 to 0.55 and orifice velocity head ratio ranges from 1.3 to 200. Simulations are performed using FLUENT V6.3 with k-ω SST model and 2nd order discretization scheme. Coarse mesh results at selected test points were compared with fine mesh results and a best meshing practice was determined. CFD computation at selected points was also performed with Realizable K-ε, v2f and RSM turbulence model. CFD predictions of discharge coefficient show good agreement with Rohde et al. experimental data.

Oil sealing in a turbocharger is a key design challenge. Under certain engine operating conditions oil in the lubrication system is likely to enter the compressor or turbine wheel crossing the piston rings which are used to arrest the undesirable oil flow. Compressor side oil leakage can cause white smoke and particulate emissions. Limited experimental and analytical methods are available to aid the designers in developing the oil flow path. The oil flow path has dimensions of the order of a few microns in certain areas and in mm in other areas. In addition, the flow is comprised of oil and exhaust gas mixture in certain regions. The combined effects of disparate geometric length scales and two-phase flow adds to the complexity of the flow. Understanding the oil flow allows the designer to correctly size the components, flow path and also specify the appropriate clearances between for instance shaft and bearing journals. In this study a Computational Fluid Dynamics (CFD) Model has been built and validated through several experiments conducted particularly to check the oil leak through the piston rings. The study shows that CFD based models can predict within engineering accuracy the flow through leakages in a turbocharger. The importance of manufacturing tolerances on the leakages is also highlighted.