Among renewable sources of energy, wind is the most widely used resource due to its commercial acceptance, low cost and ease of operation and maintenance, relatively much less time for its ...realization from concept till operation, creation of new jobs, and least adverse effect on the environment. The fast technological development in the wind industry and availability of multi megawatt sized horizontal axis wind turbines has further led the promotion of wind power utilization globally. It is a well-known fact that the wind speed increases with height and hence the energy output. However, one cannot go above a certain height due to structural and other issues. Hence other attempts need to be made to increase the efficiency of the wind turbines, maintaining the hub heights to acceptable and controllable limits. The efficiency of the wind turbines or the energy output can be increased by reducing the cut-in-speed and/or the rated-speed by modifying and redesigning the blades. The problem is tackled by identifying the optimization parameters such as annual energy yield, power coefficient, energy cost, blade mass, and blade design constraints such as physical, geometric, and aerodynamic. The present paper provides an overview of the commonly used models, techniques, tools and experimental approaches applied to increase the efficiency of the wind turbines. In the present review work, particular emphasis is made on approaches used to design wind turbine blades both experimental and numerical, methodologies used to study the performance of wind turbines both experimentally and analytically, active and passive techniques used to enhance the power output from wind turbines, reduction in cut-in-speed for improved wind turbine performance, and lastly the research and development work related to new and efficient materials for the wind turbines.
This study investigates the potential of using tilt‐based wake steering to alleviate wake shielding problems experienced by downwind turbines. Numerical simulations of turbine wakes have been ...conducted using a hybrid free‐wake analysis combining vortex lattice method (VLM) and an innovative free‐wake model called constant circulation contour method (CCCM). Simulation results indicate tilting a horizontal axis wind turbine's shaft upward causes its wake to ascend, carrying energy‐depleted air upward and pumping more energetic replacement air into downstream turbines, thereby having the potential to recover downstream turbine power generation. Wake cross section vorticity and velocity distributions reveal that the wake upward transport is caused by the formation of near‐wake streamwise vorticity components, and furthermore, the wake velocity deficit is weakened because of the skewed wake structure. Beyond the single turbine wake simulation, an inline two‐turbine case is performed as an assessment of the wake steering influence on the two‐turbine system and as an exploratory work of simulating turbine‐wake interactions using the hybrid free‐wake model. Individual and total turbine powers are calculated. A comparison between different tilting angles suggests turbine power enhancement may be achieved by tilting the upstream turbine and steering its wakes away from the downstream turbine.
Vertical-axis wind turbines (VAWTs) have a long history, with a wide variety of turbine archetypes that have been designed and tested since the 1970s. While few utility-scale VAWTs currently exist, ...the placement of the generator near the turbine base could make VAWTs advantageous over tradition horizontal-axis wind turbines for floating offshore wind applications via reduced platform costs and improved scaling potential. However, there are currently few numerical design and analysis tools available for VAWTs. One existing engineering toolset for aero-hydro-servo-elastic simulation of VAWTs is the Offshore Wind ENergy Simulator (OWENS), but its current modeling capability for floating systems is non-standard and not ideal. This article describes how OWENS has been coupled to several OpenFAST modules to update and improve modeling of floating offshore VAWTs and discusses the verification of these new capabilities and features. The results of the coupled OWENS verification test agree well with a parallel OpenFAST simulation, validating the new modeling and simulation capabilities in OWENS for floating VAWT applications. These developments will enable the design and optimization of floating offshore VAWTs in the future.
•Twin-turbine wakes depended more on rotational direction than lateral spacing.•Turbines in a counter-rotating forward setup attained the fastest wake recovery.•Wake recovery was delayed when devices ...operated with the same rotational direction.•Wake merging and evolution were highly three dimensional even up to 10D downstream.•Linear superposition of a single turbine wake represented well twin-turbine wakes.
Vertical axis wind and tidal turbines are a promising technology, well suited to harness kinetic energy from highly turbulent environments such as urban areas or rivers. The power density per occupied land area of two or three vertical axis rotors deployed in close proximity can notably exceed that of their horizontal axis counterparts. Using acoustic Doppler velocimetry, the three-dimensional wake developed downstream of standalone and twin vertical axis turbines of various shaft-to-shaft distances and rotational direction combinations was characterised in terms of mean velocity and turbulence statistics, with their impact on momentum recovery quantified. Results show that the wake hydrodynamics were more impacted by turbine rotational direction than lateral distance between devices for the range of lateral spacing considered. In the cases with turbines operating in a counter-rotating forward configuration, the wake mostly expanded laterally and attained the largest velocities that exceeded those in the single turbine case, with full momentum recovery at 5 turbine diameters downstream. The wake developed by the counter-rotating backward setup notably extended over the vertical direction, whilst devices rotating in the same direction featured the greatest lateral wake expansion with reduced velocities. Linear wake superposition of the single turbine wake provided a good representation of the mean velocity field behind twin-turbine setups. The presented results indicate that, in the design of twin-turbine arrays moving in counter-rotating forward direction, a lateral spacing of, at least, two turbine diameters should be kept as this allows the kinetic energy in the wake to be fully recovered by five turbine diameters downstream.
Two design options for a heat-recovery turbine unit (HRTU), which generates electricity for self-contained power supply of gas mains’ compressor stations (GMCSs) using the heat of exhaust gases from ...gas-turbine engines (GTEs) driving gas-pumping units (GPUs), are examined. The working fluid of the recovery circuit is octafluorocyclobutane (c-C
4
F
8
, engineering name is RC318) in one of the two HRTUs and the exhaust gases of GPU GTE in the other HRTU. The HRTU operating on RC318 has a three-circuit cycle, including three turbines, three recuperative heat exchangers, three RC318 heaters, and one common condenser. An alternative design of HRTU is a vacuum-type GTU consisting of an overexpansion gas turbine, whose inlet is connected with the exhaust of GPU GTE, exhaust gas coolers, a cooled gas compressor, and an induced-draft fan. The excess power of this HRTU above the current power demand at the GMCS is used to create a vacuum at the exhaust of the gas turbine of the GPU GTE. The results are presented of the comparative balance calculations of parameters and characteristics of both HRTUs as applied to a 16-MW Ural GPU GTE. They were performed using the updated initial data and the software library RefProp (in the CoolProp high-level interface) for the calculation of thermodynamic parameters of working fluids. It has been demonstrated that a more compact and easier to implement gas-type HRTU (with an overexpansion gas turbine), although having a lower power than the RC318-type HRTU, can still fully cover the demand of the GMCS for high-quality power and also to solve the problem of substituting imported gas piston and diesel generators at the GMCS within the shortest possible time and with the lowest capital and operating expenditures.
•Performances of four new combined power and cooling systems are compared.•Energy and exergy analyses are done for comparing the systems.•Suitable steam pressure in the heat recovery steam generator ...is identified for each system.•The system that gives higher energy output and minimum irreversibility is identified.•The gas turbine plant which is common in all contributes more than 95
In this paper, the performances of four combined power and cooling systems are compared in which the exhaust heat of a topping gas turbine plant is utilized for further power and cooling generation. Steam turbines (STs) and organic Rankine cycles (ORCs) are used for power generation by integrating those in a completely different arrangement in the first two systems while the third and fourth systems use ST based power cycles. The first and the fourth configuration uses two absorption cooling systems (ACSs) driven respectively by steam and exhaust heat. In the second and third systems, however, only one ACS is used. Energy and exergy based parametric analyses are done, showing the performance variations with HRSG steam pressure from 89 to 94 bar for comparing the CPC systems. The fourth system was found to be the most appropriate from the energetic and exergetic performance viewpoint with the first system to follow. Despite an additional ACS, the total irreversibility of the first and the fourth systems was found almost equivalent to that of the second system. Only in the third system, the total plant irreversibility was relatively less compared to the first and the fourth. It was found that the GT plant alone contributes more than 95% irreversibility in all the four systems.
In power and energy systems, both the aerodynamic performance and the structure reliability of turbine equipment are affected by utilized blades. In general, the design process of blade is high ...dimensional and nonlinear. Different coupled disciplines are also involved during this process. Moreover, unavoidable uncertainties are transported and accumulated between these coupled disciplines, which may cause turbine equipment to be unsafe. In this study, a saddlepoint approximation reliability analysis method is introduced and combined with collaborative optimization method to address the above challenge. During the above reliability analysis and design optimization process, surrogate models are utilized to alleviate the computational burden for uncertainties‐based multidisciplinary design and optimization problems. Smooth response surfaces of the performance of turbine blades are constructed instead of expensively time‐consuming simulations. A turbine blade design problem is solved here to validate the effectiveness and show the utilization of the given approach.
•Experimental and computational studies of Savonius hydrokinetic turbine.•Performance investigation of Savonius hydrokinetic turbine in low velocity condition.•Insight of design information on this ...turbine’s performance in low velocity condition.•Savonius hydrokinetic turbine versus Savonius wind turbine at the same input power.•Analysis of enhanced performance of the former turbine by flow characteristics studies.
The extensive depletion of the conventional sources of energy has forced the mankind to explore every possibilities lying beneath the nature. The evolution and modification of the old ideas from the field of wind turbine led the mankind to explore the same technology in water. Hydrokinetic turbine, one of the most emerging technologies for power generation, has gained keen interest of the researchers because of some of the unique properties of water like higher specific weight, higher momentum than air for same velocity etc. The objective of the study is to evaluate how the conventional Savonius wind turbine performs when it rotates by the momentum of water current at low velocity from 0.3m/s to 0.9m/s in an open water channel. An experimental investigation along with computational fluid dynamics (CFD) study using Ansys 14.0 has been carried out to accomplish the objective of the work. To understand the significance of Savonius design in water application, the performance of the hydrokinetic turbine is experimentally compared to the identically designed wind turbine for the same input power values, showing enhanced performance of the former turbine. The purpose of using CFD is to enable a more detailed study on the velocity and torque distribution across the hydrokinetic turbine and hence to develop more insight of design information about its performance under low velocity condition. Finally the reason for enhanced performance of the hydrokinetic turbine is investigated from the computational study of flow characteristics of both the hydrokinetic and wind turbines. Smooth, stable operation and a good service life of the hydrokinetic turbine could be expected unlike the wind turbine.
PDF
