Numerical investigation of high efficiency random fiber lasers at 1.5μm

The purpose of this paper is to present a numerical evaluation method for the aerodynamic design and development of high-efficiency exhaust diffusers in steam turbines, as well as to present the comparison between the numerical results and measured data in an actual real scale development steam turbine. This paper presents numerical investigation of three-dimensional wet steam flows in a down-flow-type exhaust diffuser that has non-uniform inlet flows from a typical last turbine stage. This stage has long transonic blades designed using recent aerodynamic and mechanical design technologies, including superimposed leakages and blade wakes from several upstream low pressure turbine stages. The present numerical flow analysis showed detail three-dimensional flow structures considering circumferential flow distributions caused by the down-flow exhaust hood geometry and the swirl velocity component from the last stage blades, including flow separations in the exhaust diffuser. The results were compared with experimental data measured in an actual development steam turbine. Consequently, the proposed aerodynamic evaluation method was proved to be sufficiently accurate for steam turbine exhaust diffuser aerodynamic designs.

Download Full-text

A Numerical Investigation of Aerodynamic Characteristics of a Deteriorated Gas Turbine

Volume 2: I&C, Digital Controls, and Influence of Human Factors; Plant Construction Issues and Supply Chain Management; Plant Operations, Maintenance, Aging Management, Reliability and Performance; Renewable Energy Systems: Solar, Wind, Hydro and Geothermal; Risk Management, Safety and Cyber Security; Steam Turbine-Generators, Electric Generators, Transformers, Switchgear, and Electric BOP and Auxiliaries; Student Competition; Thermal Hydraulics and Computational Fluid Dynamics ◽

10.1115/power-icope2017-3444 ◽

2017 ◽

Author(s):

Koichi Yonezawa ◽

Genki Nakai ◽

Kazuyasu Sugiyama ◽

Katsuhiko Sugita ◽

Shuichi Umezawa

Keyword(s):

Numerical Investigation ◽

Gas Turbine ◽

Rotor Blade ◽

High Efficiency ◽

Aerodynamic Characteristics ◽

Rotor Blades ◽

Second Stage ◽

The Third ◽

Time Operation ◽

Third Stage

In order to keep a high efficiency of a gas turbine, it is important to make a suitable maintenance. Gas turbine nozzle guide vanes (NGVs) and turbine rotor blades deteriorate through a long-time operation due to various causes such as a particle attachment, erosion, and a thermal stress. In the present study, a numerical investigation has been carried out to clarify the influence of the NGV and the rotor blade deterioration on aerodynamics in a 3-stage gas turbine. Geometries of the NGV and the rotor blade were measured from a real gas turbine using a 3-D scanner. The first stage NGVs and rotor blades usually deteriorate seriously and are usually replaced at certain intervals. Two kinds of the geometries of the NGV and the rotor blade of the first stage were obtained, which are the new ones before use and the used ones to be replaced. For the second stage and the third stage, the geometries before use were used in the computations. The numerical results show that the isentropic efficiency of the first stage increases and that of the second stage decrease due to the deterioration of the first stage. The efficiency of the third stage is not affected significantly. The mechanisms are discussed from the observation of the flow fields.

Download Full-text

All-fiber passively mode-locked femtosecond fiber lasers

10.32920/ryerson.14638536 ◽

2021 ◽

Author(s):

Jiaqi Zhou

Keyword(s):

Fiber Laser ◽

Pulse Energy ◽

Pulse Width ◽

Fiber Lasers ◽

High Efficiency ◽

Single Mode ◽

Scaling Up ◽

Mode Locking ◽

Raman Signal ◽

Loop Mirror

This dissertation presents three all-fiber designs of passively mode-locked lasers in order to achieve high pulse energy, environmentally-stable dissipative soliton (DS) operation in all-normal-dispersion cavities. A numerical model for DS mode-locked fiber lasers based on the nonlinear Schrodinger equation has been used to guide the experimental designs. Firstly, an environmentally-stable and ultra-compact SESAM mode-locked fiber laser is demonstrated. The all-fiber design is realized using a mode-field-adaptor (MFA) to couple light onto the SESAM. A polarization-maintaining fiber loop mirror serves multiple functions as a highly reflective mirror, an output coupler and polarization selector. Self-starting and stable DS mode-locking operation is achieved with 1.7 nJ pulse energy and a 22 ps pulse width. Secondly, an ultra-stable DS mode-locking was demonstrated in a long cavity ring laser with a nonlinear amplified loop mirror (NALM) as a mode-locking device. The output pulses of 32 nJ, 615 fs de-chirped pulse width were obtained with the Raman signal suppressed below -20 dB in a 81 m long cavity. The mode-locking is self-starting and the mode-locked pulse train shows excellent stability. Thirdly, the mode-laser cavity was extended with a piece of large-mode-area (LMA) fiber with a low dispersion to further scaling up the pulse energy to 56.8 nJ. The laser pulses were compressed to 750 fs by a pair of volume gratings. In the processing of scaling-up the pulse energy of the NALM mode-locked fiber laser, some interesting physical phenomena were observed, such as the operation regime transition from noise-like to DS with a sudden reduction of Raman signal and a unique waves-splitting with a stable temporal spacing. The phenomena were studied and explained in this dissertation. In addition to the mode-locked fiber laser, a CW and a Q-switched fiber lasers were also designed with a single-mode- multimode- single-mode (SMS) filter as an effective mean of overcoming nonlinear effects. The transmission spectral property of the SMS was studied which fits well with theoretical calculation. One high efficiency SMS CW fiber lasers and one SMS Q-switched fiber laser were designed which showed the effectiveness of the SMS filter for inhibiting the SRS and significantly reducing SPM.

Download Full-text