Due to expected increases in gas turbine performance, strictly related to firing temperature, heat transfer is a major issue in design processes. To keep components temperature levels below design requirements, cooling systems are commonly used. Nowadays, nozzle and blade cooling systems have reached a high degree of complexity. In a preliminary design stage, both experimental and 3D numerical analyses are usually not very suitable to define geometry, coolant mass flow rate or cooling system typology. This is mainly due to the uncertainty on several parameters, i.e. pressure distributions and materials properties, and their undefined interaction. This work presents a simulation tool useful to provide system cooling development with qualitative and quantitative information about metal temperature, coolant mass flow rate, heat transfer and much more. This tool couples energy, momentum and mass flow conservation equations together with experimental correlations for heat transfer and pressure losses. Metal conduction is solved by two dimensional calculations for several blade to blade sections. This methodology allows to investigate several cooling system configurations and compare them in a relatively short time. Main features of this simulation tool are shown comparing obtained results with experimental data.
This work deals with the influence of roughness on high-pressure steam turbine stages. It is divided in three parts. In the first one, an experimental campaign on a linear cascade is described, in which blade losses are measured for different values of surface roughness and in a range of Reynolds numbers of practical interest. The second part is devoted to the basic aspects of the numerical approach and consists of a detailed discussion of the roughness models used for computations. The fidelity of such models is then tested against measurements, thus allowing their fine-tuning and proving their reliability. Finally, comprehensive computational fluid dynamics (CFD) analysis is carried out on a high-pressure stage, in order to investigate the influence of roughness on the losses over the entire stage operating envelope. Unsteady effects that may affect the influence of the roughness, such as the upcoming wakes on the rotor blade, are taken into account, and the impact of transition-related aspects on the losses is discussed.
Self-emulsifying drug delivery systems (SEDDS), often intended for oral delivery, are normally explored in biorelevant aqueous media. The high complexity of these multi-component systems leaves the understanding of self-emulsification poor, hindering formulation rationalization. In this work, we aimed to fill this gap by studying the effects of glycerol on the self-emulsification of a ternary component formulation made of 20% w/w Tween 80, 15% w/w Span 80, and 65% w/w Captex 300 Low C6. The behavior of SEDDS in pure water and a binary mixture of water and glycerol (58.8% w/w) were investigated by optical microscopy, SAXS (small angle X-ray scattering), dynamic light scattering, and surface tension measurements. The presence of glycerol, at 58.8% w/w, altered the self-emulsification behavior by suppressing the formation of lamellar structures observed in the presence of water, reducing the droplet mean diameter from 0.2 to 0.1 μm and changing the mechanism of self-emulsification. As co-surfactant, glycerol may intercalate within the polyoxyethylene chains of the surfactant at the palisade layer, increasing the interface flexibility and expanding it. Since no free water is available at the investigated glycerol concentration, glycerol, which is also a co-solvent, may additionally modify long-range interactions by reducing Van-der-Waals attractions or giving rise to repulsive surface-solvent mediated forces of entropic origin. These effects could be exploited to rationalize SEDDS formulations, widening their use within the pharmaceutical industry.
The usual ways to measure the aerodynamic forcing function are complex and expensive. The aim of this work is to evaluate the forces acting on the blades using a relatively simpler experimental methodology based on a time-resolved pressure measurement at the rotor discharge. Upstream of the rotor, a steady three holes probe (3HP) has been used. The postprocessing procedures are described in detail, including the application of a phase-locked average and of an extension algorithm with phase-lag. The algorithm for the computation of the force components is presented, along with the underlying assumptions. In order to interpret the results, a preliminary description of the flowfield, both upstream and downstream of the rotor, is provided. This gives an insight of the most relevant features that affect the computation of the forces. Finally, the analysis of the results is presented. These are first described and then compared with overall section-average results (torque-sensor), and with the results from 3D unsteady simulations (integral of pressure over the blade surface) in order to assess the accuracy of the method. Both the experimental and the numerical results are also compared for two different operating conditions with increasing stage load
Gas turbine cooling has steadily acquired major importance whenever engine performances have to be improved. Among various cooling techniques, film cooling is probably one of the most diffused systems for protecting metal surfaces against hot gases in turbine stages and combustor liners. Most recent developments in hole manufacturing allow to perform a wide array of micro-holes, currently referred to as effusion cooling. This paper presents the validation of a simplified 2D conjugate approach through comparison with the experimental results of effectiveness for an effusion plate, performed during the first year of the European Specific Targeted REsearch Project AITEB-2 (Aerothermal Investigation of Turbine Endwalls and Blades). A preliminary test is performed with the steady-state technique, using TLC (Thermochromic Liquid Crystal) wide-band formulations. Results are obtained in terms of local distributions of adiabatic effectiveness. Average values are compared with calculations to validate the numerical code. Then, Design Of Experiment (DOE) approach is used to perform several conjugate tests (about 180), so as to derive the behavior of different effusion plates in terms of overall effectiveness and mass flow rate. Data are analyzed in detail and a correlative approach for the overall effectiveness is proposed.
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