Self-starting Ability Research Articles

Wind tunnel testing of scaled models of a newly developed Darrieus-style vertical axis wind turbine with auxiliary straight blades

Renewable sources of energy, needed because of the increasing price of fossil derivatives, global warming and energy market instabilities, have led to an increasing interest in wind energy. Among the different typologies, small scale Vertical Axis Wind Turbines (VAWT) present the greatest potential for off grid power generation at low wind speeds. In the present work, wind tunnel investigations about the performance of an innovative configuration of straight-blades Darrieus-style vertical axis micro wind turbine, specifically developed for small scale energy conversion at low wind speeds, has been made on scaled models. The micro turbine under investigation consists of three pairs of airfoils. Each pair consists of a main and auxiliary airfoil with different chord lengths. A standard Darrieus configuration, consisting of three single airfoils, was also tested for comparison. The experiments were conducted in a closed circuit open chamber wind tunnel facility available at the Laboratory of Industrial Measurements (LaMI) of the University of Cassino and Lazio Meridionale (UNICLAM). Measured data were reported in terms of dimensionless power and torque coefficients for dynamic performance analysis and static torque coefficient for static performance analysis. The adoption of auxiliary airfoils has demonstrated to give more dynamic torque at the lower wind speeds with respect to a standard Darrieus rotor, resulting in better performance for all the wind speeds considered. In terms of dynamic power coefficient, the standard Darrieus configuration presented slightly better performance for the highest wind speed analyzed. The proposed configuration showed also an higher value of static torque coefficient with respect to the standard Darrieus micro turbine, resulting in a better self-starting ability.

Numerical simulation for unsteady flow over marine current turbine rotors

The numerous benefits of Savonius turbine such as simple in structure, has appropriate self-start ability, relatively low operating velocity, water acceptance from any direction and low environmental impact have generated interests among researchers. However, it suffers from a lower efficiency compared to other types of water turbine. To improve its performance, parameters such flow pattern, pressure and velocity in different conditions must be analyzed. For this purpose, a detailed description on the flow field of various types of Savonius rotors is required. This article presents a numerical study on a nonlinear two-dimensional flow over a classic Savonius type rotor and a Benesh type rotor. In this experiment, sliding mesh was used for solving the motion of the bucket. The unsteady Reynolds averaged Navier-Stokes equations were solved for velocity and pressure coupling by using the SIMPLE (Semi-Implicit Method for Pressure linked Equations) algorithm. Other than that, the turbulence model using k-e standard obtained good results. This simulation demonstrated the method of the flow field characteristics, the behavior of velocity vectors and pressure distribution contours in and around the areas of the bucket.

Flow-Based Prediction for Self-Starting Limit of Two-Dimensional Hypersonic Inlets

Hypersonic inlet self-starting ability is of great importance for scramjet engines and hypersonic flight vehicles to operate stably and efficiently. However, the prediction of the hypersonic inlet self-starting limit is generally difficult. This paper proposes a flow-based prediction approach for the self-starting limiting internal contraction ratio of two-dimensional hypersonic inlets. The key lies in the establishment of a general approximate expression for the fluid dynamic blockage, caused by the migration of the primary separation bubble down the internal contraction portion of the inlet. Formulas for the fluid dynamic blockage and the limiting internal contraction ratio are given. The predicted results are in good agreement with the published experimental results on hypersonic inlet starting.

Fluidic Control Method for Improving the Self-Starting Ability of Hypersonic Inlets

The poor self-starting ability at low Mach number normally restricts the proper operation of hypersonic inlets within a wide Mach-number range. A fluidic control method with backflow duct based on the flowfield characteristics of the unstart flows is brought forward and investigated through a combination of computational and experimental methods. First, the uncontrolled case is studied. Results show that the baseline inlet does not start until Mach 6.1, which is too high for the researched hypersonic inlet. Then, the controlled case demonstrates that the flow separation is well controlled by means of the closed flow cycle introduced by the backflow duct. Numerical investigations indicate that the self-starting Mach number of the backflow-duct inlet declines to Mach 4.3, and starting status at Mach 5.0 and is observed experimentally. The self-starting ability of the inlet is improved remarkably; meanwhile, at high Mach numbers, the flow structure is barely impacted by the minimal backflow rate, ensuring the high-performance operation of hypersonic inlets.

Study on Charging and Discharging Characteristics of Energy Storage System in Wind Storage Power Plant under the Condition of Black Start

Grid black start refers to the process that power with self-start ability starts and leads the restart of the entire grid in "full blackout" status. In this paper, it selects the wind power plant containing energy storage device as the black-start power to study the charging/discharging problems of VRB in the self- start process in wind field.

Internal behavior of segmented fuel cell during cold start

In order to improve cold start capability and survivability of proton exchange membrane fuel cell (PEMFC), a fundamental understanding of its internal behavior is required. In this study, the cold start processes of a PEMFC with different operating conditions have been investigated, and the characteristics of current density and temperature distributions are studied through in-situ experiments with a printed circuit board (PCB). It is found that the start ability of PEMFC is strong at −3 and −5 °C, but weak at −7 and −10 °C. Also the self-start ability can be enhanced by decreasing the initial current load. Polarization curves show almost no degradation after successful cold start at −3 and −5 °C, while the PEMFC degrades a lot after failed cold start at low temperature like −10 °C. Also electrochemical impedance spectroscopy (EIS) shows a big degradation after galvanostatic mode cold starts. Local current density of segmented cell results shows that the highest current density is initially near the inlet region and then quickly moves downstream, reaching to the region near the middle eventually during the successful cold start process. However, during the failed cold start process, the highest current density is initially near the inlet region of the flow channels and quickly moves down stream, reaching the upper left corner region (A1) before shut down eventually. For both successful and failed cold starts, the highest temperature can be observed near the middle of the cell after the reaching of the highest current density.

Performance of Line-start Permanent Magnet Synchronous Motor with Novel Rotor Structure

The novel Line-start Permanent Magnet Synchronous Motor (LSPMSM) has widely industrial applications, due to its high efficiency, high power factor and self-starting ability. The starting characteristics of novel LSPMSM with rotor arc straight inserted permanent magnet are studied based on the electromagnetic field theory. A finite element model of a 3-phase 8-pole 22kW LSPMSM is developed under reasonable assumptions as well as the solving region, and the transient electromagnetic field is calculated by the coupled field circuit method. The effects due to the variation of rotor structure parameters and stator winding turns and source voltages on performance of starting torque, current and power factor are analyzed, and the lowest starting voltage is obtained. Under overall consideration, the optimal motor parameters are confirmed and the performance on rated condition is calculated. Finally, the prototype experimental results verify the numerical calculating characteristic of the models.

Numerical Simulations of Vertical Axis Wind Turbine with Controllable Blades

Wind power gives us non-polluting alternative to reduce the exploration of conventional fossil fuels.A novel vertical axis wind turbine(VAWT) has been developed that consists of several controllable plat blades.A computational investigation of the output characteristics of the VAWT has been conducted using the commercial computational fluid dynamics(CFD) code ANSYS 13.0.A validation study was performed using a Savonius turbine and good agreement is obtained with experimental data.Both fixed and rotating two-dimensional CFD simulations are conducted to further investigate the performance of the VAWT.Steady simulations have demonstrated that the VAWT has good self-starting ability with an averaged static torque coefficient of 1.09.The predicted maximum averaged power coefficient is 0.449,which is nearly 2 times of the Savonius turbine.

Experimental Study of Vertical Axis Wind Turbine with Wind Speed Self-Adapting

A small vertical axis wind turbine with wind speed self-adapting was designed. The diameter and height of the turbine were both 0.7m. It featured that the blades were composed of movable and fixed blades, and the opening and closing of the movable blades realized the wind speed self-adapting. Aerodynamic performance of this new kind turbine was tested in a simple wind tunnel. Then the self-starting and power coefficient of the turbine were studied. The turbine with load could reliably self-start and operate stably even when the wind velocity was only 3.6 m/s. When the wind velocity was 8 m/s and the load torque was 0.1Nm, the movable blades no longer opened and the wind turbine realized the conversion from drag mode to lift mode. With the increase of wind speed, the maximum power coefficient of the turbine also improves gradually. Under 8 m/s wind speed, the maximum power coefficient of the turbine reaches to 12.26%. The experimental results showed that the new turbine not only improved the self-starting ability of the lift-style turbine, but also had a higher power coefficient in low tip speed ratio.

Effects of pitch angle and blade camber on flow characteristics and performance of small-size Darrieus VAWT

This study builds up a simulation model, via Ansys/Fluent, to investigate the effects of pitch angle and blade camber on the flow characteristics and performance of small-size Darrieus vertical axis wind turbine (VAWT). The VAWT system is driven by a uniform wind speed (10 m/s). The blade profiles with three different cambers are NACA0012, 2412 and 4412, respectively; and the pitch angles vary between 10° and −10°. The user-defined function is employed to calculate the instantaneous moments produced by all the blades and rotate the VAWT system from rest. The flow structures, the vorticity fields and the performance on the blades will be addressed; also, the self-starting ability and the moment coefficient of the VAWT system are discussed. For the blade profiles studied, the initial acceleration is the largest at θ = −10° and decreases monotonously as the pitch angle increases from θ = −10° to θ = 10°. Further, at the same pitch angle, the larger the camber of the blade (NACA4412), the better is the self-starting ability of the VAWT system. The maximum root mean square moments have the maximum values at θ = 5° for all the blade profiles studied herein. The root mean square moments for NACA2412 are much higher than those of NACA0012 and 4412 at all pitch angles. However, the root mean square moments for NACA4412 are relatively insensitive to the variations in pitch angles.

A Mechanism for Self-Starting Thermal Engine

The conventional engine cannot start alone. The engine needs a special device to turn it on. This device is usually an electric motor that is called starter. Any other engine that uses another working cycle then Otto cycle or Diesel cycle could accede to a self-starting ability. The paper tries to use ancient ideas in order to develop a true thermal engine able to use solar and other renewable energy. This unconventional engine inherits some ideas from the perpetual motion machine solutions.

A study on a pole-changing operation of a single-phase written-pole motor

This paper deals with design and characteristic analysis of a pole changing written-pole motor (WPM), which is a synchronous motor with self-starting ability. The winding configuration is deliberately determined to get a pole-cha nging function, and it is confirmed by FEA with time step method. In a ddition during operation of the exciter, the characteristi cs of magnetization of magnet and synchronization of a rotor are also analyzed.

1330 ヘリックス・ダリウス形風車に関する研究

The drawback of the Darrieus type wind turbines is their low self-starting ability due to small generated torque at start. In the previous study, we have already designed a Helix-Darrieus type wind turbine applying helical twist to the basic straight Darrieus type blades along its circumference and conducted a series of wind tunnel tests. In the present study, we introduced curvature of the blades for swept-back angle to the Helix-Darrieus type blades to improve the self-startability further. The wind tunnel tests are conducted using two improved Helix-Darrieus type wind turbines havning different swept-back angles. The results show that the both torque and power coefficients at low wind speed are improved with the newly proposed Helix-Darrieus type wind turbines.

Self-starting five optical cycle pulse generation in Cr 4+ :YAG laser

We report stable self-starting near-transform-limited 26-fs pulses at 250-mW output power from a Kerr-lens mode-locked (KLM) Cr4+:YAG laser using chirped mirrors in combination with prisms. The highest output power achieved in KLM regime was 600 mW at 55-fs pulse duration. The experimental results agree well with the results of theoretical analysis with respect to KLM self-starting ability and stability against continuous-wave and multi-pulse operation. Parameter ranges for stable transform-limited KLM pulses as well as the shortest achievable pulse durations are established. Using an InGaAs-InP semiconductor saturable absorber mirror we could obtain self-starting 57-fs pulses at the average output power of 200 mW. Two-photon absorption was found to be the main mechanism favoring the multiple-pulse operation.

Theory of sub-10 fs-generation in Kerr-lens mode-locked solid-state lasers with a coherent semiconductor absorber

The results of the study of ultra-short pulse generation in continuous-wave Kerr-lens mode-locked (KLM) solid-state lasers with semiconductor saturable absorbers are presented. The issues of extremely short pulse generation are addressed in the frames of the theory that accounts for the coherent nature of the absorber–pulse interaction. We developed an analytical model that bases on the coupled generalized Landau–Ginzburg laser equation and Bloch equations for a coherent absorber. We showed, that in the absence of KLM semiconductor absorber produces 2 π-non-sech-pulses of self-induced transparency, while the KLM provides an extremely short sech-shaped pulse generation. 2 π- and π-sech-shaped solutions and variable-area chirped pulses have been found. It was shown, that the presence of KLM removes the limitation on the minimal modulation depth in absorber. An automodulational stability and self-starting ability were analyzed, too.