Analytical, computational, and experimental study on vertical axis Hydrokinetic turbines

Muluken, Temesgen Tigabu

dc.contributor.author	Muluken, Temesgen Tigabu
dc.date.accessioned	2022-12-20T12:35:50Z
dc.date.available	2022-12-20T12:35:50Z
dc.date.issued	2022-11-09
dc.identifier.uri	http://ir.bdu.edu.et/handle/123456789/14712
dc.description.abstract	The purpose of this study was to contribute to the advancement and development of hydrokinetic turbines (HKTs), with a particular focus on vertical axis hydrokinetic turbines (VAHKTs). HKTs are a comparably new energy conversion technology especially in comparison to wind turbines. The goal of this research was to investigate the key aspects of HKT’s performance, such as resource assessment, hydrodynamics design, computational analysis, and experimental evaluations. The resource assessment study were conducted for rivers and a canal in the Upper Blue Nile Basin, Ethiopia for HKTs. Various hydrodynamics methods are coupled with hydrological methods with the aim of transforming the measured flow rate or discharge into velocity data to determine the power density (PD), the available power per square meter of vertical flow area. PD were estimated over the length of the rivers and canal and estimate the PD variation over the months of the year. The Gumara, Gilgel-Abay, and Bahirdar-Abay rivers in the Blue Nile Basin were studied along with the Koga irrigation main canal apart from estimating the power density variation. Historical databases of yearly, monthly, and daily averaged discharge were used. The key elements of this analysis are (i) converting discharge into velocity for PD determination, and (ii) the period over which the velocity is averaged compared to the averaging time used to determine the HKT power curve. To predict PD, ARC-GIS was used to estimate the reach length and cross-section from raster Digital Elevation Models (DEMs). The hydraulic modeling of the velocity was done using HEC-RAS software. Field measurements were conducted to validate the hydrodynamic model. The result of the study was cross-sectional area average water velocity (V A ), which used to predict the PD. To relate the time average of velocity (V T ) to the power curve of a HKT, which in turn was used a 2-minute average velocity measurement was conducted with a total of 270 samples. It is found that 25% of the Gumara river is suitable for HKTs with a maximum of 1.4 kW/m 2 power can be extracted. The Gilgel-Abay river has a maximum velocity above 1 m/s and 3.4 kW/m 2 power that can be extracted over 32% of its length. Similarly, for Bahirdar-Abay river, over 29% of the reach length 2.6 kW/m 2 power can be extracted. The H-type vertical axis hydrokinetic turbine was designed using a hydrodynamic design model. The hydrodynamics of VAHKTs were studied using an analytical v method based on a double multi-stream tube (DMST) model. The lack of research that shows actual performance under various water velocities is a major stumbling block in the development of VAHKTs technology. To that end, a MATLAB algorithm was written to forecast performance. Operational characteristics such as power coefficient (CP ), torque coefficient (CQ ), and tips speed ratio (TSR) were used to assess the performance of VAHKTs. The operational tip speed ratio range for VAHKTs is between 1:2 T SR 3:8. The study indicated that there is no power generation from VAHKTs at T SR 4. As a result, the DMST-based MATLAB code developed in this work can be used to design and estimate the performance of VAHKTs at a low cost. A computational study was used to analyze the major problem with VAHKTs, which is the starting performance. Among their potential disadvantages is that when the load is lost, or when they start with no load, they can reach high instantaneous blade speeds before returning to a “steady” runaway speed. These high speeds can cause high loads on the blades and must, therefore, be fully understood. This thesis describes a computational investigation of the effect of inertia as a turbine starts from rest with no load and reaches runaway. Turbine inertia is modified by altering the blade density while the turbine geometry is not altered. At the minimum inertia, the added mass contributes significantly to the dynamics, and the highest overshoot occurs in blade speed. Increasing inertia damps the peak but slows the acceleration. The added mass depends on blade mass but is constant for the whole starting sequence and is independent of water speed. The results give guidance for the design of turbines to balance the minimization of the overshoot and starting time. The experimental investigation primarily serves to validate the analytical and computational studies. The experimental work was also used to determine the transient behavior of VAHKTs during runaway conditions. Torque and rotational velocity were monitored using in-house made instruments to deduce the transient behavior. It is found that at V1 = 1:45 m/s, the CFD and experiment have a strong agreement in predicting transient behavior. During the experimental investigation, the four anticipated transient behaviors of HKTs were documented. vi	en_US
dc.language.iso	en	en_US
dc.subject	ENERGY CENTER	en_US
dc.title	Analytical, computational, and experimental study on vertical axis Hydrokinetic turbines	en_US
dc.type	Thesis	en_US