Trunkline Construction

Impact of channel blockage on the performance of axial and cross-flow hydrokinetic turbines

An Experimental Investigation of the Performance of Cross-flow Hydro Turbines

The total installed capacity of the hydropower stations in Pakistan is about 7,000 MW which is about 20% of the total available hydro power potential. For possible micro-hydro stations, a potential of about 1300 MW exists at a number of low head and high flow rate sites. Work has been reported by Chattha et al. [1, 2] related to installation of a micro-hydro power station at one of the typical sites. An axial flow pump-as-turbine (PaT) was installed to generate electrical power at the micro-hydro station. The site selected for this work is quite typical and efforts are now being made to utilize the maximum potential of the site conditions. The PaT only utilizes about half of the available flow of water and a spillway was constructed at this site to divert the excess amount of water. The diverted water flows back to the main stream after bypassing the PaT. Work is now being carried out to explore the installation of a turbine in the spillway to harness the energy potential of the diverted water stream. This work includes selection, design, fabrication and installation of a turbine in order to generate electrical power utilizing the energy of water diverted to the spillway. A 100 ft3/sec flow rate with about 11 ft head is available at the spillway side. Considering these site conditions and indigenous fabrication expertise, cross flow type turbine has been selected for installation. Cross flow turbines are being manufactured in Pakistan and are usually quite successful for micro-hydro systems. Based on the available site conditions, a cross flow turbine has been designed. The diameter and length of the turbine runner have been calculated. Furthermore, the number of blades and radius of curvature have been determined along with other design parameters. The designed turbine is expected to produce about 50 kW of power. The complete design of the turbine, based on the available site conditions is presented in this paper.

Cross Flow Turbines (CFT), also known as Banki or Ossberger turbines are broadly used in small scale hydropower generation. Easy construction and operation, low CAPEX and OPEX and fairly independent efficiency from flow rate are the main characteristics of the CFT. However, they also tend to have a modest efficiency (80%), hence they are not considered for large scale power plants. Previous work have focused on use of Internal Deflectors (ID) for CFT efficiency improvement. However experimental flow observation and characterization inside CFT is hard to achieve. This work proposes use of Computational Fluid Dynamic (CFD) tools as an aid in ID design. A transient regime, two-dimensional, numerical model of a CFT without any internal deflectors was carried out. Deviation from experimental results at BEP was close to 5%. CFT w/o ID results were used as ID design starting point. Parameters: Upper Blade Position and ID Length were defined and varied obtaining six different ID versions. Numerical models were carried out for evaluation of ID effect on CFT. CFT hydraulic efficiency improvement was achieved for all ID versions studied (range 0.5%–3%, average:1.9%). Output power was also augmented (range 0.3%–4%, average:2.5%)for all cases.

Based on previous research conducted by Purwantono about the utilization of exhaust flow from a conventional cross-flow turbine prototype that was used as an inlet of tubin Kaplan [1]. This research was carried out to see how the exhaust flow velocity of each tubin before and after was combined into one combination turbine. This numerical based study uses the Ansys 18.0 application by inputting a 3D design from a conventional turbine prototype which was used as the material for this study. The results obtained in this study show the average of outlet velocity in the Kaplan turbine that uses a velocity outlet from a cross flow turbine of 0.3 m / s greater when it is combined, which is 8.33 m / s and after being combined to 0.38 m / s. The results of this study are expected to contribute to the development of conventional turbines later

Because cross-flow turbines rotate perpendicular to their inflow, the blades encounter a continually fluctuating angle of attack and relative velocity that can lead to the unsteady, non-linear phenomenon of dynamic stall. Additionally, because of appreciable deceleration of the flow through the turbine rotor (induction), the relative velocity a blade experiences during the upstream portion of its cycle differs appreciably to that of the downstream portion. Both dynamic stall severity and turbine induction depend on the ratio of the blade tangential velocity to the inflow velocity - the dimensionless ”tip-speed ratio”. Consequently, the power generated by a blade varies substantially with tip-speed ratio and angular position. As the tip-speed ratio increases, the angle of attack range experienced by the blade decreases, dynamic stall weakens, and the relative velocity incident on the blade increases. In aggregate, this increases the amplitude of the performance peak in the upstream sweep and shifts the peak later in the cycle. In contrast, as the tip-speed ratio increases, power losses during the downstream sweep becomes increasingly detrimental to time-averaged turbine performance. Recent works, both experimental and computational, have investigated the near-blade hydrodynamics of cross-flow turbines in concert with performance measurements. However, despite the significance of the downstream sweep on performance, most attention has focused on the power generating phases.
 Here, we specifically investigate the impact of the downstream blade sweep on cross-flow turbine performance using a 1-bladed turbine (NACA 0018 foil). Because turbine torque is measured at the center shaft in our experiments, a one-bladed turbine allows us to isolate the performance contributions for the upstream and downstream sweeps (i.e., with a multi-bladed turbine, the torque contribution from each blade is ambiguous). Additionally, flow fields are investigated to understand the hydrodynamic mechanisms for the observed degradation in downstream performance at high tip-speed ratios. For this purpose, two-component, phase-locked, planar particle image velocimetry data is obtained inside the turbine swept area for two tip-speed ratios. We find that the average performance in the upstream sweep continues to increase beyond the optimal tip-speed ratio, with respect to time-averaged performance, of 2.5. In contrast, the average performance in the downstream sweep is net neutral until the optimal tip-speed ratio where it begins to decrease at a faster rate than the upstream performance increases. This indicates that the optimal tip-speed ratio is strongly influenced by the point at which the downstream sweep begins to consume appreciable power. These results highlight the importance of understanding hydrodynamics in the downstream sweep, where induction and upstream disturbances violate simple models to predict angles of attack and relative velocity. An improved understanding may suggest strategies to improve performance in the downstream sweep and increase optimal tip-speed ratios and performance of cross-flow turbines.
 
 
 
 

ross flow turbines are widely used as turbines for driving micro-scale hydropower plants in rural areas, but their efficiency is still low because cross flow turbines only use one nozzle. The utilization of the potential energy of water is not optimal yet to be converted into pressure and kinetic energy of water in the nozzles with high water velocity hitting the turbine blades. The problem of cross flow turbines with one nozzle has an uneven flow of water to the turbine blades, and it is not effective in converting potential energy into power in the turbine. The purpose of this research is to develop a four-nozzle Cross Flow turbine and test its performance. The method used is to conduct experimental testing in a laboratory that tests the performance of a cross flow turbine using four nozzles. A cross flow turbine with four nozzles has better performance than a cross flow turbine using only one nozzle. The results obtained that the cross flow turbine with four nozzles where the water jets out of the nozzle is more evenly distributed and the flow of water enters the turbine blade runner, resulting in a good impulse reaction in the blades. The conclusion is that the performance of the four nozzle cross flow turbine is able to produce higher turbine rotation, power and efficiency.

Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics. Here, we experimentally investigate the effect of aspect ratio—the ratio of the blade span to rotor diameter—on the performance of a straight-bladed cross-flow turbine in a water channel. To isolate the effect of aspect ratio, all other non-dimensional parameters are held constant, including the relative confinement, Froude number, and Reynolds number. The coefficient of performance is found to be invariant for the range of aspect ratios tested (0.95–1.63), which we ascribe to minimal blade–support interactions for this turbine design. Finally, a subset of experiments is repeated without controlling for the Froude number, and the coefficient of performance is found to increase, a consequence of the Froude number variation that could mistakenly be ascribed to aspect ratio. This highlights the importance of a rigorous experimental design when exploring the effect of geometric parameters on cross-flow turbine performance.

The demand for electricity is growing rapidly around the world as economic development spreads to emerging economies. Among hydro, wind, solar, biomass and geothermal energies, hydro power can be considered as the most exciting and sustainable renewable energy resource for electricity generation, providing 19% of the planet’s electricity. A considerable amount of the global electricity production is obtained from hydropower, but with an insignificant contribution from low head rivers (i.e. ≤ 5m). The interest among researchers towards exploring and harnessing energy from low-head hydro resources is gaining more prominence in recent years. Therefore, this study was designed to investigate the competitiveness of the hydrokinetic turbine (HKT) against conventional hydro turbines for harnessing the hydropower available in low-head rivers. A vertical axis hydrokinetic turbine using NACA 0021 airfoil profile and a cross-flow turbine were the technologies employed for the study. Hydrological data were collected from the Ona River in Ibadan, Nigeria. The data were used as input for a computer simulation.In respect of the two hydropower generation technologies considered in this study. The set of mathematical equations used in the design steps for cross flowcross-flow turbine was used and computed using MATLAB. The simulation results were used to develop a scorecard for the evaluation of the two technologies. This study revealed that HKT is more suitable for a zero or low head river than a conventional hydro-turbine, such as cross-flow turbine.

Cross-flow Turbine Design for Variable Operating Conditions

Recently, the cross flow turbines attract more attention for their good performance over a large operating regime at off design point. This study employs a very low head cross flow turbine, which has open inlet duct and has barely been studied before, to investigate the performance of the cross flow turbine with air suction from the rear part of the runner. Unlike conventional cross flow turbines, a draft tube is attached to the outlet of runner to improve the turbine performance. Water level and pressure in the draft tube are monitored to investigate the influence of air suction. Torque at local blade passage of three parts of runner is examined in detail under the conditions of different air suction. Consequently, it is found that with proper air suction in the runner chamber, the water level in the draft tube gradually drops to Stage 2 of the runner and the efficiency of the turbine can be raised by 10%. Overall, the effect of air-layer on the performance of the turbine is considerable.

An evaluation was made of the design and hydromechanical performance characteristics for three basic turbine types: axial flow (Jonval), inward radial flow (Francis) and crossflow (Banki). A single commercially available turbine representative of each type and within the appropriate power range (<5hp) was obtained for evaluation. Specific turbine selections were based on price, availability and suitability for operation at heads of 50 feet or less and flows under 2 cubic feet per second. In general, the peak operating efficiencies of each unit tended to be lower than anticipated, falling in the range of 40 to 50%. With sufficient flow, however, significant useful power outputs up to 3 hp were obtained. While the radial flow turbine (a centrifugal pump operated as a turbine) had the lowest initial unit cost, the axial and cross flow designs exhibited more stable operation, particularly under transient loadings. The crossflow turbine had the added advantage that it was essentially self-cleaning. With further developmental effort and appropriate design modifications it should be possible to bring each of these microhydro designs to their full performance potential.

Large‐scale hydropower plants have major impacts on surrounding environment. This is mostly because of flooding land for the reservoir which destroys forests, wildlife habitat, agricultural, and scenic lands (Union of Concern Scientists [2015]: Environmental impacts of hydroelectric power). Small‐scale hydropower systems, on the other hand, can be used as a much environmental choice especially for independent rural electrification. Dam or barrage requirements for mini and micro turbines are fairly small and water is stored in forebay tanks. However, financial considerations dictates utilisation of more efficient turbine technologies than currently available small‐scale turbines can offer. Cross flow turbines (CFT) of small‐scale hydropower plants are highly environmental considering their production and maintenance, but unfavoured due to their difficulty in achieving adequate and sustainable efficiency. Furthermore, maintaining power quality of micro hydropower stations with island operation setup is difficult. In this study, response surface methodology (RSM) is applied to investigate and identify the operating conditions of a micro cross flow turbine. A quadratic model is developed through RSM and an experimental setup of CFT is established to investigate the combined effects of flow rate, head and guide vane angle parameters on the turbine performance. RSM analyses are performed for 50 Hz constant frequency as optimal working condition. © 2015 American Institute of Chemical Engineers Environ Prog, 34: 1506–1511, 2015

One of the solutions to overcome the lack of electricity problem in rural area is Crossflow pico-scale hydropower. In improving cross-flow turbine performance, understanding fluid phenomena is needed. Particle image velocimetry (PIV) measurement is one of the methods used to visualize the fluid flow phenomena inside the turbine. Expensive price of seeding particle leads to find the solution for this PIV method. The objective of this study is to use a cheap seeding particle from cheaper materials, mainly resin and rhodamine B. Besides that, in this study, PIV measurement is compared to 2D computational fluid dynamics (CFD) with multiphase volume of fluid model. From the results, several phenomenon can be observed at both of the methods (PIV and CFD) such as separation in the blade tip. Therefore, this study showed that an inexpensive material resin and rhodamine B as a seeding particle has a potential and ability to represent flow inside pico-hydro cross-flow turbine.

The dead band in the performance of cross-flow turbines: Effects of Reynolds number and blade pitch