The self-starting performance of vertical-axis wind turbines (VAWTs) is crucial for their widespread utilization. Conventional evaluation methods using the static torque coefficient (CTS) or self-starting time have limitations. "The minimum 1st derivative of angular acceleration in the lift acceleration state" is proposed to serve as a suitable indicator for the completion of self-starting. Understanding the behavior of the self-starting process in VAWTs is crucial for optimizing power output. A comprehensive methodology is used that integrates experiments and computational fluid dynamics (CFD). Wind tunnel experiments are conducted to evaluate the self-starting and power output performance of the turbines. CFD is employed utilizing the Fluent 6DOF module to investigate the torque and flow field characteristics during the self-starting process. Additionally, the objectives of our study are to investigate the effect of static evaluation methods on the dynamic start-up process and to explore the effects of airfoil type, pitch angle, and inlet wind speed on the self-starting behavior of turbines. The results indicate that a high CTS ensures initial rotation, but the subsequent self-starting time remains independent of this factor. Increasing the pitch angle enhances the self-starting performance. At an inlet speed of 5 m/s, for the NACA2418 airfoil turbine, the self-starting times for pitch angles of 10° and 5° are reduced by 20% and 12%, respectively, compared to that for 0°. The NACA0018 airfoil turbines with pitch angles of 0° and 5° fail to complete self-starting. The airfoil type also plays a crucial role, with the NACA2418 airfoil demonstrating superior self-starting performance and power performance. Furthermore, the minimum self-starting wind speed of the NACA0018 airfoil turbine was explored and determined be between 5.5 m/s and 6 m/s. The utilization of this novel self-starting evaluation method addresses the limitations of traditional approaches, providing a more universally applicable interpretation of the characteristics of turbine self-starting behavior.

In order to study the effect of temperature on the pore structure of lignite, liquid nitrogen adsorption and scanning electron microscopy (SEM) were used to analyze the change of pore structure of Indonesian lignite after heating, and the relationship between fractal dimension and pore structure of lignite after heating was analyzed. The effect of drying temperature on the pore structure of lignite was investigated by effective moisture diffusion coefficient and X-ray diffraction (×RD). The results show that between 40 and 160 ℃, with the increase of drying temperature, the N₂ adsorption and desorption of Indonesian lignite shows a trend of first increasing and then decreasing. The fractal dimensions D₁ and D₂ of some lignites have a linear relationship with the specific surface area and average pore diameter, respectively, and the fractal dimension D₃ has a linear relationship with the average pore diameter. As the drying temperature increases, the moisture transfer resistance decreases and the effective moisture diffusivity of lignite ( $D_{\mathrm{e}\mathrm{f}\mathrm{f}}$) increases accordingly. There is a linear positive correlation between $D_{\mathrm{e}\mathrm{f}\mathrm{f}}$ and the average pore diameter. The increase of the lignite aromatic system and the decrease of the crystallite stacking height have certain effects on the pore structure of lignite.

Aiming to explore the limitation of Hardgrove Grindability Index (HGI) and broken behavior of lignite, coal samples were ground for different minutes in the Hardgrove mill. Experiments show that the grinding kinetics can describe the grinding process of coal well. For the same kind of coal, the grinding kinetic parameters k and m of a certain particle size can be regarded as constants. The particle size of the particles to be ground R has a power function relationship with the parameter k. The initial particles appeared selective grinding during the grinding process. From the perspective of the index T₁₀ (a size of 1/10 of the initial particle size) and grinding rate, HGI has a poor description of continuous lignite grinding. In this case, the grinding kinetic parameter k of the same size of lignite can be used to discuss the grindability of different coal samples. Generally, the larger the k of the same size coal, the higher the grindability. The lattice size and mosaic morphology of ash forming minerals affect the grinding rate of coal samples. Raw coal with low ash content is more likely to liberate a large amount of minerals in the early stage of grinding.

The accurate prediction of the flow field characteristics of complex mountains is of great practical significance for the development and construction of wind farms, but it is not yet fully understood. The main purpose of this study is to propose a method for the study of flow field characteristics under complex mountain conditions, which can optimize the boundary conditions required for numerical simulation through the wind acceleration ratio and, at the same time, couple the numerical simulation and wind measurement data to reflect the real mountain flow field distribution. The results show that the proposed method has good applicability in complex mountain wind farms, can reproduce the real flow field distribution, and has a certain practical value. Wind speed distribution and turbulence intensity are greatly affected by boundary conditions such as wind speed and wind direction and are also affected by the shielding effect brought by terrain changes. The contrast between 120° and 150° wind direction is more obvious. When the incoming wind moves to the top of a mountain or the ridgeline, it will form a low-speed wake area behind it, resulting in reduced wind speed, increased turbulence intensity, and an unstable flow field.