Global warming and increasing environmental pollution have driven scientists and engineers to new methods of harnessing energy. This thesis research will use CFD analysis to study the efficiency of converting kinetic water energy into electrical energy in a pipe for a Rim Driven Turbine (RDT), which offers the advantage of being easily installed in drainage and watercourse systems become Previous research in the field of RDT has shown that the field contains many research gaps that need to be addressed, such as a lack of material on parameters that affect performance, including cavitation, geometry and simulations involving different environmental conditions.
The results show that installing the RDT in series reduces the pressure drop in each turbine while nearly doubling the power output for the same pipe pressure head. Also, I would like to express my gratitude to my supervisor, Professor Basman Elhadidi, who allowed me to research this field and guided me during my MSc thesis. Last but not least, I am grateful to Professor Luis Rojas-Solórzano, whose comments and recommendations helped me approach the problem from a new perspective.
Introduction
- Background
- Literature Review
- Investigation of Application Areas
- Numerical & Experimental Studies of RDT
- Studies on Blades Cavitation
- Summary
- Motivation
- Pressure Loads and Power Output
- Research Objectives
The flow of water through the blades moves the blades and converts the kinetic energy of the fluid into electrical energy. Furthermore, they initiated a similar work (Song, 2022) focused on numerical analysis of the performance of RDTs in real-case scenarios. Although the thrust experiments seem out of scope, they provide essential data on counter-rotation of the blades.
Accordingly, Jian et al. be his job. extended to the numerical analysis of RDT turbines where counter-rotation of the blades is assessed. At the same time, four previous researches were directly related to our CFD study of the RDT turbines. Therefore, it was decided to carry out a numerical analysis that will assess the hydrodynamic performance of the RDT turbines, where high Re numbers will be taken into account.
Methodology
- OpenProp configuration
- Computational Domain and Boundary Conditions
- Mesh of the 3-bladed turbine
- Mesh of the 6-bladed Turbine
- Mesh of the 3-bladed series turbines
- Solution Method
- Effect of simulating with velocity and pressure inlets
- Grid Independence Test
The flow of water moves upstream in the positive y direction, while x and z coordinates represent horizontal and vertical axes. 5, the geometric model is divided into unstructured mesh with an element size of 10 mm at the MRF zone. In contrast, the rest of the calculation domain is divided into a mesh of 70 mm size.
6, the MRF zone was discretized with a denser mesh with a growth rate of 1.2, which is suitable for fluid flow problems. In addition, it is important to check the accuracy of the solution by observing the pressure distribution on the blade surface; thus, geometric zones of high curvature were approximated with a high mesh concentration, which is the turbine blades in our case. Similar to the 3-blade case, the mesh for the 6-blade turbine will consist of unstructured tetrahedral mesh with an average element size of 10 mm in the MRF zone and 70 mm in the rest of the domain, as shown in Fig.
Identical to the 3-leaf cases, the MRF zone consists of dense mesh with high curvature. Note that additional wings increased the mesh count almost twice, indicating high mesh concentration in the center, as shown in Fig. The intervention of in-series turbines followed a similar approach with unstructured tetrahedral mesh with a high concentration in MRF zones.
However, for the three-bladed series turbines, it was decided to involve only two turbines for the initial research. In addition, the front turbine has been shifted to increase the accuracy of the MRF in a stable solution. It is important to note that each hydro turbine operates in a TSR range that generates a corresponding power coefficient, characterized by formulas (1) and (2). 3) Here 𝐶𝑝 represents the effectiveness of the entire turbine, measuring the portion of energy converted from the kinetic energy of the water into force (3) compared to the energy available in the surrounding fluid, and TSR shows the ratio between the speed at a tip of a blade and the magnitude of the free stream velocity.
Further results are generated using the pressure inlet simulation, as it closely approximates the physical reality where the movement of the water is caused by pressure differences. Note that the methodologies mentioned above imply two ways to generate varying TSR, the first being recording inlet values as in the velocity-inlet simulation example and changing angular velocities. Second, defining a constant angular velocity in the MRF zone and changing the inlet values as in the pressure inlet example.
Results and Discussion
Results Comparison: 3-bladed vs. 6-bladed turbine
The numerical results suggest that increasing the number of blades, as in the case of a 6-blade turbine compared to a 3-blade turbine, does not significantly improve the power coefficient. Although it is slightly higher at low TSR values, this can be attributed to errors in the steady-state simulation. In conclusion, the increase in power coefficient achieved by increasing the number of blades in a single turbine is insufficient to justify the additional economic expenditure.
Pressure drop analysis in the simulated domain shows that one 6-blade turbine is susceptible to elevated pressure drop values. The high pressure drop can eventually cause fatigue and damage to the blades, reducing the life compared to a single turbine with three blades. These findings suggest that a single turbine with three blades has a better power coefficient in the long run.
Counter Rotating Series 3-bladed Series Turbines
26, we can see the high-pressure loads on opposite sides of the leading edges, which match their direction of rotation in Fig. Note the swirling flow behind each MRF zone, which is recovered by the trailing turbine blades. However, it may have a lower power coefficient due to less drag and reduced blade pressure.
Therefore, it is necessary to calculate the amount of energy produced, the power coefficient and the pressure drop to evaluate the stability of the turbines in series. 29, the swirl area marked with red and green lines is relatively smaller than the front swirl area in the blue-cyan particles, implying that a rear turbine is recovering some of the energy from the front swirl. Theoretically, it is possible to calculate the maximum number of sustainable turbines in series based on Fig.
However, the main purpose of installing turbines in series was to achieve distributed loads to reduce system failure. The first turbine therefore experiences a pressure drop of 750 kPa, significantly lower than 1 kPa, which corresponds to a single hydro turbine. Therefore, it is concluded that placing the turbines in series reduces the pressure load on the turbines and reduces the chance of failure of the entire system.
Results Comparison for All Cases
The turbine results were calculated over the entire operating TSR range and show that the 6-blade and 3-blade single-blade turbines demonstrate superior coefficients of performance, with the former outperforming the latter. In contrast, in-series turbines show lower power output, achieving 60% of ambient kinetic energy at a peak TSR of 8.25, compared to 3- and 6-bladed turbines, which achieve maximum power coefficients of 0.6 at TSR of 8.92 and 8.90, respectively. 33, it can be said that the single 6-blade turbine has the highest pressure loads on the blade surface, which may have a detrimental effect on its operating life.
This is mainly attributed to its higher solidity, which results in a larger area exposed to pressure loads from the incoming water, leading to increased air resistance and energy generated, as well as reduced service life. In addition, it is suggested that 6-bladed turbines have a higher generated power but a lower lifetime compared to their 3-bladed counterparts; the latter exhibit comparatively lower compressive loads due to their lower solidity. The pressure loads are further reduced in the case of 3-blade two turbines, which is evident from the two pressure drops observed in the computational domain, corresponding to the location of the two turbines.
In conclusion, our hypothesis of sequential turbine placement reducing pressure on both turbines is supported by the results, with the front and rear turbines experiencing much lower pressure loads on their blade surfaces. However, it is essential to consider the amount of power produced in order to draw conclusions about the viability of serial turbines.
Generated Power Comparison
In summary, a number of RDT turbine designs were developed and analyzed on ANSYS Fluent, leading to several significant findings on turbine design and performance. First, the results showed that a 3-bladed hydro turbine with a specific blade design could convert up to 67% of the surrounding water's kinetic energy into mechanical (and subsequently electrical) energy. Second, the proposed series placement of the turbines reduced the thrust load on the blades by 62.5% for the forward turbine.
It was concluded that although series turbines exhibit lower power coefficients than a 6-blade and 3-blade single-blade turbine, it produces a greater amount of power and has a longer operating life and less fatigue due to of pressure loads distributed on the blades. The results imply that an additional turbine can increase the power output of the overall system by a significant margin. In contrast, the power output of a single 6-blade turbine model was found to be similar to that of a single 3-blade turbine, suggesting that adding more blades to a single turbine has limited impact positive in producing its power.
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