فهرست مطالب pooyan hashemi tari

To date, due to growing investment in renewable energies, researchers are interested in wind power feasibility studies for mountainous terrains. Numerical Weather Prediction (NWP) methods has proved to be a strong tool to simulate wind flow field in real time. In present study, using NWP method and in particular WRF (weather research and forecasting model) software, the wind flow, over Martigny mountainous area located in Switzerland, has been simulated and studied. Due to high resolution of the simulation, Large Eddy Simulation (LES) has been employed to perform turbulence modelling. The objective of this study is to assess the credibility of WRF in wind simulation and to examine the effect of horizontal and vertical resolutions as well as two different sub-grid scale turbulence models. The results reveal that WRF is able to generate the wind flow in comparison with those data obtained from wind measurement stations and it can properly produce diurnal wind patterns. The results also show a promising simulation for the region, located within a wide and flat valley. However, the discrepancies between the results and those obtained from the wind station, are bold for regions located at high mountainous locations and at the peaks. Smagorinsky 3d SGS turbulence model show a better performance at mountain peaks in comparison with TKE1.5 model. In addition, increasing vertical resolution reduces the discrepancy and improves WRF performance.

Concerns about the usage of fossil fuels have led to more attention to renewable energies such as wind energy. Utilization of wind turbines in the urban industry is one of the challenging topics in wind energy area. Particularly, due to the limitations of the wind conditions in the urban areas (i.e. low speed wind, high level of variation of wind direction and high turbulence level) and the space limitations within the cities, utilization of vertical axis wind turbines in micro scales have become of interest. The focus of the present study is on these types of turbines and assessing the parameters affecting their aerodynamic performances. Two types of vertical axis wind turbines (Savonius and a straight blade Darrieus) were designed and constructed in micro-scale. The effect of wind speed on the Savonius turbine is experimentally studied. Results show that this turbine performs better at lower wind speeds. The effect of the aspect ratio and the vertical position of the blade struts on the performance of the Darrieus turbine is also experimentally assessed. The results show that the best vertical position for struts is the tip of the blades. It was also experimentally observed that the turbine with aspect ratio one has the best aerodynamic performance.

Phase Change Materials (PCMs) are known to be capable of storing a substantial amount of energy in relatively low volume. Also, since the phase change process occurs in a nearly constant temperature, PCMs are suitable to be used as storage units. The present study focuses on the effect of Heat Transfer Fluid (HTF) flow parameters on heat transfer and melting process of PCM. The numerical results are validated against available experimental data. Then, the numerical study is extended to investigate the impacts of HTF flow parameters such as inlet temperature and mass flow rate. According to the obtained numerical results, the overall performance of the system is enhanced by increasing the inlet parameters of the HTF flow. In addition, the exergy analysis indicated that the stored exergy increases with increasing flow rate and inlet temperature of HTF. On the other hand, the exergy efficiency does not increase monotonically, but it reaches its maximum value in intermediate values of inlet flow rate and temperature.

Nowadays, as the wind turbines become widespread, it is important to study the turbine behavior in real conditions which may be oscillatory or unsteady. Identifying the characteristics of airfoils used in HAWT blades in different operating conditions can predict the turbine’s aerodynamic performance with acceptable accuracy. In this research, NACA 4412 airfoil has been studied and its performance characteristics such as lift coefficients drag coefficient, surface pressure distributions in subsonic flow field at different angles of attack and Reynolds numbers have been investigated. For this purpose, RANS & URANS governing equations are employed for analysis of static & oscillating conditions respectively using two different turbulence models (Spallart- Almaras and "K-ω" ) have been used. Numerical solution results show acceptable agreement with experimental results. Furthermore, the aerodynamic characteristics with oscillating flow field and the effect of Reynolds number and reduced domain variation has been investigated. The results show that as the value of the reduced domain parameter increases, the lift coefficient increases, but drag coefficient, especially at low angles of attack, does not change significantly.

Using wind turbines in urban areas is one of the most challenging issues in using wind energy. due to the complex structure of urban areas, the fluid flow turbulence and the change in wind speed in these areas is significant. It is common that vertical axis (Darrieus-Savonius) wind turbines in that operate independently of the wind direction is commonly used. In this research, a comprehensive overview of major studies in this area has been carried out. In addition, challenges of using a variety of vertical axis wind turbines are mentioned. on of the challenge in this topic is using a hybrid wind turbines, with two types of Darrieus and Savonius. Darrieus turbines have high power coefficient, While Savonius turbines have the ability to start very well even at low wind speeds. In this research, it has been studied to make this system more functional and some suggestion have been presented. In order to eliminate the destructive effect of the Savonius turbine rotor on the Darrieus turbine rotor at high wind speeds, a mechanical clutch is proposed for separating these two rotors at high rotational speeds.