Basic Analysis of Counter-Rotating Turbines

Author(s):  
R. Cai ◽  
W. Wu ◽  
G. Fang

A comprehensive basic analysis for various counter–rotating turbines is given with the blade element stage assumption. Similar to the classical analysis of common turbine stages, the appropriate independent variables and evaluation criteria of the counter–rotating turbine stages are first presented and then three typical kinds of rotating blade rows are defined and all possible typical schemes of counter–rotating turbine stages are enumerated. Their performances of specific work, load factor distribution between two counter–rotating shafts and efficiency are analysed and discussed for different shaft rotating speed ratios. This information is useful for the selection and preliminary design of a counter–rotating turbine. From the analysis results, it is concluded that the load capacity per unit engine length of counter–rotating turbines can be much higher than that of common turbines (approximately twice) without efficiency penalty or even with higher efficiency. Some triple counter–rotating turbines suitable for three shaft gas turbine power plants are proposed and analysed briefly too.

Author(s):  
Chaofeng Li ◽  
Zengchuang Shen ◽  
Zilin Chen ◽  
Houxin She

The vibration dissipation mechanism of the rotating blade with a dovetail joint is studied in this paper. Dry friction damping plays an indispensable role in the direction of vibration reduction. The vibration level is reduced by consuming the total energy of the turbine blade with the dry friction device on the blade-root in the paper. The mechanism of the vibration reduction is revealed by the variation of the friction force and the energy dissipation ratio of dry friction. In this paper, the flexible blade with a dovetail interface feature is discretized by using the spatial beam element based on the finite element theory. Then the classical Coulomb-spring friction model is introduced to obtain the dry friction model on the contact interfaces of the tenon-mortise structure. What is more, the effects of the system parameters (such as the rotating speed, the friction coefficient, the installation angle of the tenon) and the excitation level on blade damping characteristics are discussed, respectively. The results show that the variation of the system parameters leads to a significant change of damping characteristics of the blade. The variation of the tangential stiffness and the position of the external excitation will affect the nonlinear characteristics and vibration damping characteristics.


2015 ◽  
Vol 5 (2) ◽  
pp. 89
Author(s):  
Munzer S. Y. Ebaid ◽  
Qusai Z. Al-hamdan

<p class="1Body">Several modifications have been made to the simple gas turbine cycle in order to increase its thermal efficiency but within the thermal and mechanical stress constrain, the efficiency still ranges between 38 and 42%. The concept of using combined cycle power or CPP plant would be more attractive in hot countries than the combined heat and power or CHP plant. The current work deals with the performance of different configurations of the gas turbine engine operating as a part of the combined cycle power plant. The results showed that the maximum CPP cycle efficiency would be at a point for which the gas turbine cycle would have neither its maximum efficiency nor its maximum specific work output. It has been shown that supplementary heating or gas turbine reheating would decrease the CPP cycle efficiency; hence, it could only be justified at low gas turbine inlet temperatures. Also it has been shown that although gas turbine intercooling would enhance the performance of the gas turbine cycle, it would have only a slight effect on the CPP cycle performance.</p>


Author(s):  
Deqi Yu ◽  
Jiandao Yang ◽  
Wei Lu ◽  
Daiwei Zhou ◽  
Kai Cheng ◽  
...  

The 1500-r/min 1905mm (75inch) ultra-long last three stage blades for half-speed large-scale nuclear steam turbines of 3rd generation nuclear power plants have been developed with the application of new design features and Computer-Aided-Engineering (CAE) technologies. The last stage rotating blade was designed with an integral shroud, snubber and fir-tree root. During operation, the adjacent blades are continuously coupled by the centrifugal force. It is designed that the adjacent shrouds and snubbers of each blade can provide additional structural damping to minimize the dynamic stress of the blade. In order to meet the blade development requirements, the quasi-3D aerodynamic method was used to obtain the preliminary flow path design for the last three stages in LP (Low-pressure) casing and the airfoil of last stage rotating blade was optimized as well to minimize its centrifugal stress. The latest CAE technologies and approaches of Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA) and Fatigue Lifetime Analysis (FLA) were applied to analyze and optimize the aerodynamic performance and reliability behavior of the blade structure. The blade was well tuned to avoid any possible excitation and resonant vibration. The blades and test rotor have been manufactured and the rotating vibration test with the vibration monitoring had been carried out in the verification tests.


Author(s):  
Kai Cheng ◽  
Zeying Peng ◽  
Gongyi Wang ◽  
Xiaoming Wu ◽  
Deqi Yu

In order to meet the high economic requirement of the 3rd generation Pressurized Water Reactor (PWR) or Boiling Water Reactor (BWR) applied in currently developing nuclear power plants, a series of half-speed extra-long last stage rotating blades with 26 ∼ 30 m2 nominal exhaust annular area is proposed, which covers a blade-height range from 1600 mm to 1900 mm. It is well known that developing an extra long blade is a tough job involving some special coordinated sub-process. This paper is dedicated to describe the progress of creating a long rotating blade for a large scaled steam turbine involved in the 3rd generation nuclear power project. At first the strategy of how to determine the appropriate height for the last-stage-rotating-blade for the steam turbine is provided. Then the quasi-3D flow field quick design method for the last three stages in LP casing is discussed as well as the airfoil optimization method. Furthermore a sophisticated blade structure design and analyzing system for a long blade is introduced to obtain the detail dimension of the blade focusing on the good reliability during the service period. Thus, except for CAD and experiment process, the whole pre-design phase of the extra-long turbine blade is presented which is regarded as an assurance of the operation efficiency and reliability.


2006 ◽  
Vol 129 (1) ◽  
pp. 106-111 ◽  
Author(s):  
Koichi Matsuda ◽  
Shinya Kijimoto ◽  
Yoichi Kanemitsu

The whirl instability occurs at higher rotating speeds for a full circular fluid-film journal bearing, and many types of clearance configuration have been proposed to solve this instability problem. A clearance configuration of fluid-film journal bearings is optimized in a sense of enhancing the stability of the full circular bearing at high rotational speeds. A performance index is chosen as the sum of the squared whirl-frequency ratios over a wide range of eccentricity ratios, and a Fourier series is used to represent an arbitrary clearance configuration of fluid-film bearings. An optimization problem is then formulated to find the Fourier coefficients to minimize the index. The designed bearing has a clearance configuration similar to that of an offset two-lobe bearing for smaller length-to-diameter ratios. It is shown that the designed bearing cannot destabilize the Jeffcott rotor at any high rotating speed for a wide range of eccentricity ratio. The load capacity of the designed bearings is nearly in the same magnitude as that of the full circular bearing for smaller length-to-diameter ratios. The whirl-frequency ratios of the designed bearing are very sensitive to truncating higher terms of the Fourier series for some eccentricity ratio. The designed bearings successfully enhance the stability of a full circular bearing and are free from the whirl instability.


2014 ◽  
Author(s):  
Jacob Weimann ◽  
Matthew Schmidt ◽  
Arthur Bergles ◽  
Marc Compere

The global water nexus is still in the formative stages as a area of study. The needs are mostly clear: people need adequate water for drinking, for growing food, for cooling steam-based power plants, and for sustaining the natural habitats that keep the carbon and hydrologic cycles functioning properly. What has emerged is a growing awareness of how finite the earth’s water resources are and how this creates a complex set of interconnected challenges in both developed and developing nations. What has also emerged are predictions with increasing urgency for water and energy crises in the next 20–50 years, especially if these concerns are left unaddressed. The Water-Nexus is not new, but its emerging importance now is driven primarily by population growth, climate change, and our growing awareness of societal impact on ecosystems. Providing energy for buildings, homes, and transportation is an increasingly difficult task for the growing population and aging infrastructure. Most individual issues within the Water-Energy Nexus are fairly well known with quantifiable water impacts. What is lacking is a clear representation of the Nexus relationships that show how changes in one sector impact another. What is needed is a compact way to represent the interrelationships that provide both insight and perspective on how much influence one proposed change has compared to another. Such an understanding should surface the most strategic, viable methods for simultaneously meeting water and energy needs while being a good steward of finances and natural resources. We propose the use of decision matrices from engineering design to represent the interconnected relationships that form the Water-Energy Nexus. The customers in this case are water-centric stakeholders such as government and corporate decision makers, educators, and water-oriented development agencies. Both quantitative and qualitative research methods are used to integrate the nexus topics into the decision matrix. Both positive and negative correlations in water impacts are indicated with their relative level of influence. Common units are used when possible to quantify water consumption or savings. Decision matrices are presented for transportation fuels and utility power generation. The transportation fuels matrix includes evaluation criteria for water impact, sustainability, convenience, emissions, public opinion, and geographic considerations. The utility power decision matrix has similar evaluation criteria except capacity factor is considered instead of convenience. These criteria are intended to aid policy makers in strategically navigating the legislative and policy generation process to emphasize or reduce emphasis on different fuel types. Recommendations are provided for strategic, viable methods to mitigate future effects of the Water-Energy crisis.


Author(s):  
R. Yadav ◽  
Sunil Kumar Jumhare ◽  
Pradeep Kumar ◽  
Samir Saraswati

The current emphasis on the development of gas turbine related power plants such as combined and steam injected is on increasing the plant efficiency and specific work while minimizing the cost of power production per kW and emission. The present work deals with the thermodynamic analysis of intercooled (both surface and evaporative) gas/steam combined and steam injected cycle power plants. The intercooling has a beneficial effect on both plant efficiency and specific work if the optimum intercooling pressure is chosen between 3 and 4. The evaporative intercooler is superior to surface type with reference to plant efficiency and specific work.


Author(s):  
A. Agazzani ◽  
A. F. Massardo ◽  
T. Korakianitis

This paper presents optimized cycle performance that can be obtained with systems including a Closed Cycle Gas Turbine (CCGT). The influence of maximum temperature, minimum temperature and recuperator effectiveness on cycle performance is illustrated. Several power-plant arrangements are analyzed and compared based on: thermodynamic performance (thermal efficiency and specific work); enabling technologies (available at present); and developing technologies (available in the near term or future). The work includes the effects of utilization of high temperature ceramic heat exchangers and of coupling of CCGT systems with plants vaporizing Liquid Hydrogen (LH2) or Liquefied Natural Gas (LNG). Given the versatility of energy addition and rejection sources that can be utilized in closed gas-cycle systems, the thermodynamic performance of power plants shown in this paper indicate the remarkable capabilities and possibilities for closed gas-cycle systems.


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