Aerodynamic performance sensitivity analysis of blade design for a 100 kW HAWT

Wind energy is gaining ever increasing popularity among renewable energy sources. In some European countries installed wind turbine capacity has reached over 20 % of the total power generation capacity. This paper examines aerodynamic performance sensitivity of wind turbine blades for main design variables. The sensitivity analysis has been conducted on a sample 100 kW three-bladed horizontal axis wind turbine (HAWT). Taguchi robust design techniques and orthogonal arrays have been used to perform experimental optimization using five main parameters: airfoil NACA profile, root chord length, tip chord length, root radius and chord profile distribution along the blade’s length. The airfoil profiles and their aerodynamic data are taken from the NACA airfoil database for which experimental lift and drag coefficient data are available. The airfoils for the studied blades have the same profile from root to tip. Three sets of analyses have been performed according to three different base load wind speeds. The sensitivity results have been presented for the optimal tip speed ratio values

Evaluation of pressure-stiffness coupling in brush seals

Brush seals are comprised of fine diameter fibers densely packed between retaining and backing plates. To achieve seal compliance bristles are arranged to contact rotor with some lay angle. When axial pressure load is applied, bristles interlock and get stuck at the backing plate, and seal stiffness varies under operating conditions. Operating stiffness is critical to determine seal-rotor contact pressure and wear life. Typically, seal stiffness is measured by pressing a curved shoe to brush bore as reported in open literature. Due to the complex nature of pressure-stiffness bristle behavior, static and unpressurized measurements cannot represent actual working seal stiffness. This work presents a brush seal stiffness measurement system that is capable of measuring seal stiffness under working pressure and speed conditions. Rotor speed is achieved by an integrated spindle drive, while contact forces are measured via sensitive load cells. Rotor excursions are applied through lateral motions of the seal housing that is actuated by a motorized linear slide. Stiffness testing methodology and calibration procedure are discussed. Comparative experimental data are presented for both static pressurized and dynamic-pressurized stiffness tests

Brush seals and common issues in brush seal applications

Brush seals are receiving wider acceptance with growing number of successful turbomachinery sealing applications over the past couple of decades. Due to their complaint nature these seals can recover from large transient rotor interference occurrences without any appreciable sustained damage or permanent performance loss. They are formed by a multitude of flexible fine bristles tightly clamped between two metal plates. When subjected to operating pressures and rotor interference, the frictional interactions between thousands of bristles result in very complex seal behavior. Brush seals are known to exhibit load path dependent hysteresis behavior. They also experience increased stiffness under differential pressure loads. While pressure distribution induces some radial forces to close the bristles towards rotor, mechanical interlock and interbristle frictional effects may lead to seal hung up after large rotor interference. In this paper, typical aspects of brush seals are presented. Complex seal behavior and common issues with brush seal applications are also discussed. Recommendations and suggestions for successful seal design are provided

Evaluation of brush seals for oil sealing applications

After proven performance in gas turbine secondary flow and hot gas path sealing applications, brush seals are being considered for oil and oil mist applications in aero-engines and industrial turbines. In oil sealing applications shear heating and oil coking are major concerns. The field experience indicates that shear heating and oil coking issues can be managed if seal is designed properly. When seal stiffness is well controlled, combined with proper fiber material selection and leakage cooling, shear heating and oil coking issues can be managed. Field experience from early gas turbine bearing sump applications suggest reduced oil mist ingestion and compressor blade fouling with no observable coking issues. Brush seal operating clearance determines leakage rate and oil temperature rise. Balancing these two conflicting performance criteria requires the knowledge of bristle hydrodynamic lift. In this work, some background on analytical solution to bristle lifting force and shear heating is presented. Based on short bearing approximation, the analytical solution suggests a strong dependence of seal clearance and hydrodynamic lift force on oil temperature and viscosity. The hydrodynamic lift force relation has been expanded to include oil temperature variability due to rotor speed and lift clearance. Results are also compared with the experimental data obtained from the dynamic oil seal test rig

3-D ANALYSIS OF A HIGH DENSITY BRUSH WITH FRICTIONAL CONTACT INTERACTIONS

The physical complexity of dense brush structures presents major challenges to analyzers. As they maintain their flexibility at elevated temperatures, which are typical in gas turbines, high density brush seals made of super-alloy bristles found popularity among engine designers. Typically brush-rotor contact occurs at very high surface speeds. If not managed properly, this may result in extreme wear conditions and damage to rotor. In order to ensure engine operational safety brush contact loads should be controlled through seal design and detail analysis. In addition to the physical complexity of these dense brush structures, frictional contacts among the bristles themselves, between the bristles and the support plates, and between the bristles tips and the high speed rotor further increase the analysis complexity, and make it a major undertaking if not impossible. Detailed understanding of brush seal contact loads is necessary to estimate seal and rotor wear performance. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. This work presents a 3-D computational brush seal structural FE model that can be used to calculate bristle stress, tip force, and do wear analysis. The analysis includes a representative brush segment with bristles formed by 3-D beam elements. Bristle interlocking and frictional interactions (interbristle, bristle-backing plate and bristle-rotor) are included to better simulate pressure-stiffness coupling. Various analysis results are presented and compared to full scale seal wear tests

An overview of wind turbine manufacturing experience in Turkey

While wind energy has been utilized by windmills for ages, 1970s oil crises was a turning point for many developed governments to initiate massive efforts to develop modern wind turbines. Starting from almost none in early 1980s, the installed wind power capacity has reached 159.2 GW globally by the end of 2009. While the use of wind turbines for general power utilization dates back to 1986 with a 55 kW capacity, it took another decade for wind farms to appear in Turkey. The Electricity Market Regulatory Authority (EPDK) started accepting wind power production licenses in 2007 reaching to a total of 78 GW wind capacity. As of today, the installed wind power capacity of Turkey is 1329 MW. The Electrical Power Resources Survey and Development Administration (EIEI) plans for a total of 20 GW wind energy within 10 years. In line with the global trend, it will be realistic to estimate Turkish wind market to reach 40 GW before 2030. There is extensive industrial infrastructure that will support production of large wind turbines in Turkey. However, due to lack of turbine technology and know-how only a limited portion of this infrastructure is used towards wind turbine production. Recently Ministry of Energy has initiated the National Wind Energy Systems Project (MILRES) with funding from TUBITAK (The Scientific and Technological Research Council of Turkey). The project aims to develop turbine technologies up to 2.5 MWs as well as to coach potential component manufacturers to develop production capabilities for large turbines

Leakage performance of a novel turbomachinery shaft seal

Advanced sealing systems are needed to control parasitic leakage flows to achieve high turbine engine efficiency and low emissions. Typical extreme turbomachinery engine operating conditions when combined rotor excursions do not lend simple sealing solutions. This work presents an in-depth analysis of a novel robust yet simple sealing system that is capable of maintaining long life under high speed and high temperature operating conditions. The proposed seal design is actually a gas bearing that is carefully tailored, analyzed, and designed to function as a differential pressure seal. The design involves a simple rigid/semi-flexible seal ring that is attached to a stationary support plate via flexible metal cloth structure. The seal body is capable of moving under the effect of hydrodynamic lift force. Therefore, above a certain clearance limit, which ensures that asperity contact is avoided, the seal follows shaft excursions to avoid damaging hard rubs

Modeling and control of a variable speed variable pitch angle prototype wind turbine

This paper focuses on modeling, control and simulation of a 500 KW horizontal axis prototype wind turbine that is being developed in the context of the MILRES (National Wind Energy Systems) Project in Turkey. The prototype turbine is designed as variable speed variable pitch angle wind turbine due to its advantages in efficiency and the structure. Aerodynamic, mechanical and electrical subsystems along with pitch and torque controllers are designed in both Matlab/Simulink and S4WT simulation environments. The main control purpose is to generate a power curve that is close to the ideal power curve where the energy efficiency is maximized below the nominal wind speed of 11 m/s and the power is limited to the nominal value above the nominal wind speed. Turbsim is integrated with both environments to generate a realistic wind profile of Kaimal turbulence model. The performance analysis of the prototype turbine is done under the power production scenario in both environments. Start up, emergency stop, shut down and parked scenarios are also implemented in S4WT

Topology optimization of a 500kW wind turbine main load frame

As wind turbines get larger and larger, nacelle weight becomes more important as it affects cost, logistics and even turbine natural frequencies. This work presents a nacelle weight optimization process for a main load frame of a 500 kW wind turbine. While the weight is minimized structural strength has been preserved. In order to achieve an effective weight reduction, topology optimization methodology is used with the aid of finite element solvers like OPTISTRUCT. Combined wind, generator and gravity loading condition have been considered while stress analyses are conducted. The work started with an initial over safe 7000 kg design. Through topology optimization iterations 28.57 % weight reduction has been achieved. Using SIMP method, weight reduction or material removal locations were carefully identified. The redesigned nacelle main frame has maximum stress levels less than 40% of the material yield strength

3-D analysis of high density brush stiffness with friction-pressure coupling

Achieving efficient sealing around high speed rotating bodies poses real engineering challenges. In recent years, dense brush structures found common use in turbomachinery sealing applications. As they maintain their flexibility at elevated temperatures, which are typical in gas turbines, high density brush seals made of super-alloy bristles found popularity among engine designers. Inherent flexibility of brush seals allows fibers to compact under pressure load. Due to the frictional interaction between the fibers and the backing plate as well as within the fibers themselves, brush seals are known to exhibit pressure stiffening and hysteresis behavior. While hysteresis affects seal performance after a rotor excursion, pressure stiffening is critical in determining heat generation and seal wear during hard rubs. Typically brush-rotor contact occurs at very high surface speeds. If not managed properly, high contact loads may result in extreme wear and damage to rotor. In order to ensure engine operational safety brush seal stiffness should be controlled through seal design and detail analysis. In addition to the physical complexity of these dense brush structures, frictional contacts among the bristles themselves, between the bristles and the support plates, and between the bristles tips and the high speed rotor further increase the analysis complexity, and make it a major undertaking if not impossible. The complicated nature of bristle behavior under various combinations of pressure load and rotor interference requires computer analysis to study details that may not be available through analytical formulations. This work presents a 3-D computational brush seal structural FE model that can be used to calculate bristle forces. The analysis includes a representative brush segment with bristles formed by 3-D beam elements. Bristle interlocking and frictional interactions (interbristle, bristle-backing plate and bristle-rotor) are included to better simulate pressure-stiffness coupling. The results indicate that rotor interference has some effect on seal tip forces in the absence of any pressure loading. However, upon application of small pressure loads, seal stiffness is generally dominated by pressure-stiffness coupling