Nowadays wind energy is one of the main growing renewable energy sources, reaching about the 6% of the global electricity demand in 2018. The number of emerging countries is growing too at the cost of heavy consumption of coal and fossil fuels to produce electrical power. The current research is focusing on improving conventional horizontal axis wind turbines (HAWT) and on finding other ways to exploit wind energy. One of the most promising ways to do it is to exploit the Magnus effect which can generate high lift on spinning devices, such as cylinders, invested by winds. Amongst the different ways to produce electrical power with the Magnus effect, the focus of this thesis is on the horizontal axis Magnus wind turbine (MWT) for small scale power production. The MWT could be a good solution to harvest both strong winds and weak winds, with velocities down to 2÷3 m/s, which happen to be the most repeatable ones. Furthermore the MWT could be a standalone solution for remote areas with weak winds that are not reached by the electrical grid. The literature on the subject is still short and some studies are badly reported, some are superficial and some don’t provide enough data to give solid bases for further studies. The present work aims to give a full overview on the current knowledge on the subject, to underline all the design issues to take into consideration and to investigate the aerodynamics of the MWT and its improvements techniques by means of RANS numerical simulations. The main objective is to give a more solid theoretical base for further experimental studies. Results show that this kind of system is potentially very rangeable, being capable of harvesting energy from both weak winds (3 m/s) and stronger winds (10÷13 m/s). The operational range can be extended to even faster than 25 m/s winds, which is the typical cut-out wind speed for conventional HAWT, by reducing the power coefficient to operate the turbine in safety. This rangeability is given by the possibility to regulate the rotation of the turbine by regulating the rotational speed of the cylinders. The maximum computed efficiencies reach the 35-40% with weak winds and can be kept also with stronger winds. Furthermore results suggest that the efficiency can be increased further (at least by 5%) by applying spiral fins on the cylinders. Further experimental studies are needed to thoroughly characterize this kind of system and to optimize its configuration.
Nel 2018 la produzione annuale di energia eolica è cresciuta del 9.6%, raggiungendo i 591 GW e coprendo il 6% del fabbisogno elettrico planetario. Anche il numero di paesi emergenti è in continua crescita ed insieme a questi, aumenta il consumo di carbone e combustibili fossili per produrre energia elettrica, essenziale per lo sviluppo di un paese. La ricerca attuale è focalizzata sui miglioramenti delle prestazioni degli aerogeneratori ad asse orizzontale convenzionali (HAWT) e sulla sperimentazione di modi alternativi per sfruttare l’energia eolica. Lo sfruttamento dell’effetto Magnus è tra i più promettenti metodi non convenzionali per estrarre energia dai venti. L’effetto Magnus permette di generare elevata portanza su cilindri rotanti investiti dal vento. Tra i vari tipi di aerogeneratori ad effetto Magnus, questa tesi si focalizza sulle turbine di Magnus ad asse orizzontale (MWT) per produzione di energia su piccola scala. Questi dispositivi sono una potenziale soluzione per estrarre energia da venti sia forti che deboli, con velocità fino a 2÷3 m/s, che sono statisticamente più ripetibili. Le turbine di Magnus potrebbero inoltre fungere da generatori indipendenti in aree remote, con venti deboli e non raggiunte dalla rete elettrica. Al momento la ricerca su questi sistemi è ancora poco documentata e buona parte degli studi in merito non forniscono sufficienti dati, sono mal documentati o superficiali. L’obiettivo della presente tesi è quello di dare una completa panoramica sull’attuale conoscenza in materia, individuare i problemi progettuali e investigare l’aerodinamica delle turbine di Magnus tramite simulazioni CFD per fornire una più solida base teorica per i futuri studi sperimentali. I risultati di questo studio mostrano che questo tipo di sistema è potenzialmente molto versatile, essendo in grado di estrarre energia sia da venti deboli (3 m/s) che da venti più forti (10÷13 m/s). L’operatività può essere estesa anche a venti superiori ai 25 m/s, tipica velocità di cut-out per le turbine convenzionali, riducendo il coefficiente di potenza per operare in completa sicurezza. Questa versatilità è data dalla possibilità di regolare la rotazione della turbina cambiando la velocità di rotazione dei cilindri. Le massime efficienze calolate raggiungono il 35-40% con venti deboli e possono essere mantenute anche con venti più forti. I risultati suggeriscono inoltre che le efficienze possano essere aumentate ulteriormente (almeno del 5%) avvolgendo alette a spirale attorno ai cilindri. Ulteriori studi sperimentali sono necessari per caratterizzare questo tipo di sistema accuratamente e per ottimizzarne la configurazione.
Aerodynamics of Magnus wind turbines
VENTURELLI, ALESSANDRO
2018/2019
Abstract
Nowadays wind energy is one of the main growing renewable energy sources, reaching about the 6% of the global electricity demand in 2018. The number of emerging countries is growing too at the cost of heavy consumption of coal and fossil fuels to produce electrical power. The current research is focusing on improving conventional horizontal axis wind turbines (HAWT) and on finding other ways to exploit wind energy. One of the most promising ways to do it is to exploit the Magnus effect which can generate high lift on spinning devices, such as cylinders, invested by winds. Amongst the different ways to produce electrical power with the Magnus effect, the focus of this thesis is on the horizontal axis Magnus wind turbine (MWT) for small scale power production. The MWT could be a good solution to harvest both strong winds and weak winds, with velocities down to 2÷3 m/s, which happen to be the most repeatable ones. Furthermore the MWT could be a standalone solution for remote areas with weak winds that are not reached by the electrical grid. The literature on the subject is still short and some studies are badly reported, some are superficial and some don’t provide enough data to give solid bases for further studies. The present work aims to give a full overview on the current knowledge on the subject, to underline all the design issues to take into consideration and to investigate the aerodynamics of the MWT and its improvements techniques by means of RANS numerical simulations. The main objective is to give a more solid theoretical base for further experimental studies. Results show that this kind of system is potentially very rangeable, being capable of harvesting energy from both weak winds (3 m/s) and stronger winds (10÷13 m/s). The operational range can be extended to even faster than 25 m/s winds, which is the typical cut-out wind speed for conventional HAWT, by reducing the power coefficient to operate the turbine in safety. This rangeability is given by the possibility to regulate the rotation of the turbine by regulating the rotational speed of the cylinders. The maximum computed efficiencies reach the 35-40% with weak winds and can be kept also with stronger winds. Furthermore results suggest that the efficiency can be increased further (at least by 5%) by applying spiral fins on the cylinders. Further experimental studies are needed to thoroughly characterize this kind of system and to optimize its configuration.| File | Dimensione | Formato | |
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Descrizione: Aerodynamics of Magnus Wind Turbines
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https://hdl.handle.net/10589/164355