Investigation of High-Pressure Turbine Endwall Film-Cooling Performance Under Realistic Inlet Conditions

Progress in materials and manufacturing techniques allows an increase of the mean turbine inlet temperature, resulting in improved efficiency and specific power of the turbine. Because of the combustor characteristics, thermal and aerodynamic nonuniformities can be present at the turbine inlet section. Then, a further increase in the inlet temperature might also generate harmful conditions for vane endwalls. In other words, it is necessary to apply realistic turbine inlet temperature and velocity profiles to evaluate these real effects. The objective of the present work is to predict and analyze a cooled high-pressure vane in terms of adiabatic effectiveness and aerodynamic behavior. An endwall cooling geometry with both fan-shaped and cylindrical holes has been investigated. Inlet nonuniformities in total temperature and velocity profile have been considered in order to simulate realistic conditions. Once the inlet total temperature profile is imposed, a considerable increase in the laterally averaged adiabatic cooling effectiveness, generated by the radial total temperature distribution, can he achieved. The inlet swirl limits this gain of cooling efficiency since it modifies the horseshoe vortex development and generates a stronger passage vortex with a detrimental effect for the platform cooling.

Influence of the Hydraulic System Layout on the Stability of a Mixed Islanded Power Network

François Avellan, Stefano Giacomini, Christian Landry, Christophe Nicolet

Numerical simulation and stability analysis of an islanded power network comprising 40 MW of hydropower, 20 MW of wind power and 60 MW of gas-fired power plant are investigated. First, the modeling of each power plant is fully described. The wind farm is modeled through an aggregated model approach of 10 wind turbines of 2 MW and comprises a stochastic model of wind evolution with wind gust. The hydraulic power plant comprises the upstream reservoir, a 1000 meters gallery, a surge tank, the 500 meters long penstock feeding a low specific speed pump-turbine and connected to the downstream tank through a 70 meters long tailrace water tunnel. The model of gas-fired power plant includes an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between. To predict the performance of the gas turbine engine, both at design and off-design conditions, performance maps are integrated in the modeling. Then, the capability of the hydraulic power plant to compensate wind power variations or load rejections is investigated using the EPFL simulation software SIMSEN to perform time domain simulation of the entire mixed islanded power network. This study shows the evolution of the response time of the hydraulic part as function of the penstock length and highlights the influence of the hydraulic layout on the power system stability. The dynamic performances of such hydraulic power plants are of highest interest for improving stability of mixed islanded power network, but require reliable simulation model of the entire network for safety and optimization purposes.

Springer Singapore2014

Turbulent scale resolving modelling of rotating stall in low-pressure steam turbines operated under low volume flow conditions

Ivan William McBean, Benjamin Megerle, Peter Ott

Non-synchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Unsteady computational fluid dynamics (CFD) has been applied to simulate the rotating stall phenomenon in two model turbines. It is shown that the investigated flow field presents a challenge to conventional Reynolds-averaged Navier–Stokes equations simulations. The modelling has been enhanced by applying scale-resolving turbulence modelling, which can simulate large-scale turbulent fluctuations. With this type of simulation a qualitative and quantitative agreement between CFD and measurement for the unsteady and time averaged flow field has been achieved. The results of the numerical investigation allow for a detailed insight into the dynamic flow field and reveal information on the nature of the excitation mechanism. It is concluded that the CFD approach developed can be used to assess LSMB blade designs prior to model turbine tests to check whether they are subjected to vibration under LVF

2015

Integrated Design, Optimization, and Experimental Realization of a Steam-Driven Micro Recirculation Fan for Solid Oxide Fuel Cell Systems

Patrick Hubert Wagner

This thesis presents the results of the design and experimental investigation of a patented 10 kWel solid oxide fuel cell (SOFC) system with a thermally-driven anode off-gas recirculation (AOR) fan, the so-called fan-turbine unit (FTU). The system has the advantage of higher global fuel utilization, and thus higher efficiencies and/or lower local fuel utilization, increasing the fuel cell stack lifetime. Electrical net DC efficiencies, based on the lower heating value (LHV) of 65 % for a global fuel utilization of 92 % are demonstrated with a system simulation and optimization. This correlates to an electrical gross DC efficiency based on the LHV of 69 %. Additionally, the waste heat of the SOFC stack can be used for local cogeneration in heating or cooling applications leading to a net utilization ratio (cogeneration of heat and electricity) of 90 %. Other advantages of this system design include the absence of a water supply, a simplified water treatment system, and the reduction of the evaporator and pump component size, which reduces the system's initial and maintenance costs. A first FTU proof-of-concept was designed, manufactured, and extensively experimentally tested. The radial inducer-less fan with a tip diameter of 19.2 mm features backward-curved prismatic blades with a constant height. Prior to coupling the recirculation fan with the SOFC, the fan was experimentally characterized with air at 200 °C. At the nominal operational point of 168000 rpm, the measured inlet mass flow rate was 4.9 kg/h with a total-to-total pressure rise of 55 mbar, an isentropic total-to-total efficiency of 55 %, and a power of 18 W. Although the consumed fan power is very low, this FTU can increase the net efficiency of a 10 kWel SOFC system by five percentage points. The fan and shaft are propelled by a radial-inflow, partial-admission (21 %), low-reaction (13 %) steam turbine with prismatic blades. This turbine has a diameter of 15 mm and consists of 59 rotor blades with a radial chord of 1 mm and a blade height of 0.6 mm. At the design point, it has a total-to-total pressure ratio of 1.9, an inlet mass flow rate of 2.1 kg/h, and an isentropic total-to-static efficiency of 38 %, yielding a power of 36 W. To the best of the author's knowledge, it is one of the smallest steam turbines in the world. The shaft features one single-sided spiral-grooved thrust and two herringbone-grooved journal gas film bearings. Nominally, these bearings operate with water vapor at temperatures up to 220 °C. The bearings were tested with ambient air, hot air, and water vapor to rotational speeds up to 220000 rpm, suggesting very stable operation (rotor orbit less than 0.002 mm). Within this work, the recirculation unit operated for more than 300 hours. In a final step, the FTU was coupled in-situ to a 6 kWel SOFC system, reaching electrical gross DC efficiencies, based on the LHV, of 66 % in part load (4.5 kWel) and 62 % in full load (6.4 kWel) for a global fuel utilization of 85 %. To the best of the author's knowledge, this was the first time that a steam-driven AOR fan was demonstrated in-situ with an SOFC system.

EPFL2019

Integrated Design, Optimization, and Experimental Realization of a Steam-Driven Micro Recirculation Fan for Solid Oxide Fuel Cell Systems

Patrick Hubert Wagner

EPFL2019