Experimental evaluation of the velocity profiles and performance of a counter rotating micro-turbine by 2D laser Doppler velocimetry

The most exploited renewable energy at a global scale is hydropower, which nowadays accounts for the 18 % of the world’s electricity supply. Its production is expected to increase approximately 3.1% each year in the next 25 years maintaining its share in the mix of electricity sources. Concerning small scale hydropower, some of the current research is focusing on the limitation of the environmental impact and economical investments. The development of energy recovery systems on existing water utility networks is a new challenge for increasing the sustainability of hydroelectricity generation. The concept of the new counter rotating micro-turbine braces this goal by allowing the recovery of the energy which is spoiled in pressure reducing valves in the water supply network. The performance of the micro-turbine prototype has been evaluated through experimental campaigns involving pressure, torque, discharge measurements and 2D Laser Doppler Velocimetry (LDV). A dedicated transparent casing equipped with flat windows has been built in order to perform undistorted optical measurement and to limit the refraction and reflection of the laser beam. The velocity profiles of the axial and tangential components have been measured for several radial positions at the inlet, in the gap between the two runners and at the outlet section of the micro-turbine prototype. Numerical simulations and a further study on the mass equation applied to the investigated cross-sections of the machine have been carried out in order to complete the velocity profile where the optical access to perform LDV measurements had been blocked. These experimental methods grant a full study on the velocity profiles. The energy equation, applied to the outlet sections of both runners, allows the investigation of the flow behavior and of the related machine performance. The results back up further improvements of the runner blades shape.

Hydraulic performance evaluation of a micro-turbine with counter rotating runners by experimental investigation and numerical simulation

Loïc Andolfatto, François Avellan, Cécile Münch-Alligné, Elena Vagnoni

The development of energy recovery systems on existing water utility networks is a new challenge for increasing the sustainability of electricity generation mix. The concept of the new micro-turbine with counter rotating runners braces this goal by allowing the recovery of the energy which is spoiled in pressure reducing valves in many water supply networks. The hydraulic performances of the micro-turbine are evaluated through an analysis on the angular momentum balance applied to the investigated cross-sections of the machine. For this analysis, an experimental campaign involving 2D Laser Doppler Velocimetry (LDV) is performed to measure the velocity field of the flow at the inlet and outlet sections of the machine. Since the optical access to perform LDV measurements is blocked close to the hub of the runners, a further analysis on the mass balance and numerical simulations are performed to complete the velocity profiles and to evaluate the machine performance. The combination of numerical and experimental methods grants a full study on the operating condition of the micro-turbine and strengthens the results achieved. The results back up the best operating condition of the machine for different discharges and support further improvements of the runner blades shape.

2018

Optimization of low-head hydropower recovery in water supply networks

Irene Almeida Samora

Small scale hydropower is emerging as a decentralized source to satisfy local demand for electricity. The interest in micro-hydropower, which refers to installed power below 100 kW, is increasing since this is a solution with low environmental impact. Water supply systems are one of the main manmade water systems presenting potential for micro-hydropower. Although some applications already exist in adduction lines, the urban distribution networks remain unexplored. Because these are complex systems in which flows and pressure vary constantly, specific technology and installation schemes for energy recovery are lacking. This work accesses the potential for hydropower within water supply networks (WSN) and presents an arrangement of micro-turbines specially conceived for this type of installation. The arrangement is based on a novel inline turbine suitable for pressurized systems and its best location within the networks is studied. The five blade tubular propeller (5BTP), preliminarily designed in the framework of the European Project HYLOW, was further developed and tested in this work. An experimental campaign was conducted with a large range of heads and torque measurements to access its characteristic curves and to obtain hill charts. The relative positioning of the turbine-generator shaft regarding the pipe bend was modified from a downstream position to an upstream position. Efficiencies of around 60% were found. The adequate locations in WSN for micro-hydropower plants are identified using an optimization algorithm which considers both the assessment of the energy production and sizing of the main equipment and works. A concept for the implementation of the 5BTP in the field was developed, consisting of an arrangement with up to four turbines inline within a buried chamber created around an existing pipe. Two objective functions, energy production and economic value respectively, are used. A simulated annealing process is developed to optimize the location of a given number of turbines. This procedure takes into account the hourly variation of flows throughout an average year and its effect on the turbine efficiency. The optimization is achieved by considering the characteristic and efficiency curves of a turbine with different impeller diameters and simulating the annual energy production in a coupled hydraulic model. After a convergence analysis for different restrictions and numbers of installed turbines, the algorithm was applied to analyze the feasibility of the proposed arrangement in two case studies in Switzerland: a sub-grid of the city of Lausanne and the complete WSN of the city of Fribourg. In both cases, the implementation of the proposed energy recovery solution seems to be feasible. A detailed analysis of the cost breakdown revealed that the cost of additional pipe work, which are required in each layout to guarantee a by-pass supply in case of maintenance, may have an important role on the investments. Also, the pressure reduction valves locations, if they exist, are likely to be the optimal solutions. Finally, a methodology to quantify the potential for hydropower based on the excess energy in a WSN is proposed and applied to case studies. It allowed to conclude how much the proposed arrangement can extract from the networksâ energy potential. In addition, an attempt was made to produce an expedite method to estimate the energy produced with one 5BTP based on network parameters and dimensional analysis.

EPFL2016

Analytical hill chart towards the maximisation of energy recovery on water utility networks with counter rotating micro-turbine

Loïc Andolfatto, François Avellan, João Nuno Gomes Borga Delgado, Cécile Münch-Alligné, Elena Vagnoni

Existing water utility networks provides a wide, distributed and unexploited hydropower potential. The installation of energy recovery stations on existing infrastructures limits both the required investment and the environmental impact. The counter-rotating runners micro-turbine presented in this paper is a new technology dedicated to the harvesting of energy on drinking water network. An analytical model of the machine’s efficiency – the so-called hill chart – is used to investigate the runners’ speeds command laws that maximize the recovered energy on the wide range of consumer-driven flow discharge experienced on water utilities.

2015

Optimization of low-head hydropower recovery in water supply networks

Irene Almeida Samora

EPFL2016