FarmConners market showcase results: wind farm flow control considering electricity prices

The EU and UK have made ambitious commitments under the net-zero plans to decarbonise their economies by 2050. For this, offshore wind will play a major role, significantly contributing to a paradigm shift in the power generation and greater volatility of electricity prices. The operating strategy of wind farms should therefore move from power maximisation to profit maximisation which includes income from providing power system services and the reduction of maintenance costs. Wind farm flow control (WFFC) is a key enabler for this shift through mitigation of wake effects in the design and operation phases. The results of the FarmConners market showcases presented here are the first attempt to economically assess WFFC strategies with respect to electricity market prices. Here, we present a conceptual simulation study starting from individual turbine control and extend it to layouts with 10 and 32 turbines operated with WFFC based on the results of five participants. Each participant belonged to a different research group with their respective simulation environments, flow models and WFFC strategies. Via a comparative analysis of relative WFFC benefits estimated per participant, the implications of wind farm size, the applied control strategy and the overall model fidelity are discussed in zero-subsidy scenarios. For all the participants, it is seen that the income gain can differ significantly from the power gain depending on the electricity price under the same inflow, and a favourable control strategy for dominant wind directions can pay off even for low electricity prices. However, a strong correlation between income and power gain is also observed for the analysed high-electricity-price scenarios, underlining the need for additional modelling capabilities to carry out a more comprehensive value optimisation including lower prices and system requirements driven cases.FarmConners market showcase results: wind farm flow control considering electricity pricespublishedVersio

Down-regulation and individual blade control as lifetime extension enablers

As more and more wind turbines are coming close to the end of their design lifetime, evaluation of end of life strategies is becoming highly relevant. Moreover, as turbine technology matures and wind farms grow larger, lifetime extension becomes a financially attractive option compared to re-powering and decommissioning. Present work suggests control strategies, namely down-regulation and individual blade control, as lifetime extension enablers. The concept of using them as retrofit control implementations is explained. Their individual and combined potential in fatigue load reduction is evaluated, along with their effect on other performance and pitch system metrics. Finally, the possible period of extension, beyond the nominal 20 years, is evaluated in an example case where the retrofit control strategy is applied after 15 years of baseline operation. The aeroelastic simulations are performed with a 10 MW reference wind turbine, according to load certification standards. Results show that the two methods complement each other in load alleviation. The pitch actuator demands are also significantly decreased when the two methods are combined

Νumerical simulation and flow analysis in the final section of a Pelton turbine distributor

194 σ.Η παρούσα εργασία εκπονήθηκε στη Σχολή Μηχανολόγων Μηχανικών του Ε.Μ.Π. και έχει ως στόχο την προσομοίωση και μελέτη της ροής στο τελικό τμήμα συστήματος διανομής υδροστροβίλου δράσης (Pelton-Turgo). Πιο συγκεκριμένα, μελετάται η επίδραση στη ροή του βάκτρου (που φέρει την ρυθμιστική βελόνη) και των πτερυγίων στήριξης αυτού, στο εσωτερικό του τελευταίου ευθύγραμμου τμήματος του αγωγού διανομής μετά από γωνία 90 μοιρών. Η διάταξη αυτή υπάρχει στους περισσότερους υδροστροβίλους δράσης μικρής ισχύος και η γεωμετρία που χρησιμοποιήθηκε είναι αυτή του ακροφυσίου του πειραματικού μοντέλου υδροστροβίλου Pelton που υπάρχει στο εργαστήριο Υδροδυναμικών Μηχανών της Σχολής. Η μοντελοποίηση και αριθμητική επίλυση της ροής σε αυτή την διάταξη έγινε με την χρήση των εμπορικού λογισμικού υπολογιστικής ρευστομηχανικής, της εταιρείας Ansys, Fluent. H επεξεργασία των αποτελεσμάτων έγινε με χρήση των λογισμικών Tecplot 360, Excel καθώς και υπολογιστικού προγράμματος σε Fortran. Οι υπολογισμοί έγιναν για την ονομαστική παροχή του υδροστροβίλου. Αρχικά, μελετήθηκε η ροή σε αγωγό με γωνία χωρίς εσωτερικές διαμορφώσεις ενώ κατόπιν εξετάστηκε η επίδραση του βάκτρου και των πτερυγίων σε αυτή. Στη συνέχεια, εξετάστηκε η επίδραση των πτερυγίων σε σχέση με το μήκος τους, την σχετική τους γωνία και το πλήθος τους. Μεταβάλλοντας αυτές τις παραμέτρους δημιουργήθηκαν διάφορες γεωμετρίες οι οποίες μελετήθηκαν και αξιολογήθηκαν με κριτήριο την μείωση των υδραυλικών απωλειών στον αγωγό, την ελαχιστοποίηση των δευτερευουσών στροβιλισμών που αναπτύσσονται κατά την εγκάρσια διατομή αλλά και την κατά το δυνατόν εξομάλυνση της ροής κατά μήκος της διάταξης. Τα αποτελέσματα έδειξαν ότι η παρουσία των πτερυγίων παίζει σημαντικό ρόλο στον περιορισμό των δευτερευουσών ροών. Στα καλύτερα από αυτά, που επετεύχθησαν σε μία από τις γεωμετρίες με τα 4 πτερύγια, οι εφαπτομενικές ταχύτητες μειώθηκαν στο μισό σε σχέση με την περίπτωση χωρίς πτερύγια.The present diploma thesis was developed at the School of Mechanical Engineering of National Technical University of Athens and has as object of study the numerical simulation and flow analysis in the final section a Pelton turbine distributor. More precisely, the influence in the flow structure of the ribs, which support the needle of the nozzle and the driving rod, at the final straight section of the distributor after a 90o bend was examined. This kind of geometrical configuration is common in small scale impulse turbines with two nozzles. The geometry of the model is based on the experimental Pelton turbine model which is installed at the Laboratory of Hydrodynamic Machines of NTUA. The curvatures of the distributor result to an increase of tangential velocities and therefore adverse secondary flows which in turn, according to recent studies, affect the jet quality and lead to hydraulic efficiency losses. Several different rib configurations were examined by changing their count (2,3 and 4), length and angular position. It was found that the presence of ribs does play an important role in restricting secondary flows. The best results were achieved in one of the 4-rib cases where the tangential velocities were reduced by half compared to the no-ribs case. Numerical simulations were performed for the flow field using the commercial computational fluid dynamics Fluent software with water as the working fluid for the nominal operating point of the turbine. The post-processing of the results was done using Tecplot 360, Excel and a Fortran code.Βασίλης Κ. Πέττα

Investigation on the potential of individual blade control for lifetime extension

In recent years the focus of wind energy industry is on reducing levelized cost of energy by rotor upscaling. Moreover, a current topic of interest to both industry and academia is the extension of lifetime to existing wind turbines approaching the end of initial design span. Thus, the need for load alleviation technologies integrated in the design process or for retrofit purposes is becoming more relevant. One of these is individual blade pitch control, a recurring topic in research, with known advantages and weaknesses namely the pitch actuator and bearing wear. The present work suggests such a system incorporating three independent controllers with input the root bending moments on the rotating frame. The linear system used for controller design is based on black box identification of non-linear simulations and filters are used both for the input and output. Different setups of the independent blade control scheme are applied on a 10 MW reference turbine, with a large and highly flexible rotor representative of the current industrial status, under wind conditions as defined by relevant certification standards. The investigation aims on evaluating the system’s performance based on the fatigue load alleviation potential for different components as well as identifying the tradeoff for each design choice. Finally, based on basic assumptions the reductions are translated to possible life time extension for each component based on a combined operation where the new controllers are applied for a percentage of the initial 20 year lifetime

Towards integrated wind farm control: Interfacing farm flow and power plant controls

Concepts for control of wind farms (WFs) can be clustered into two distinct concepts, namely, wind power plant control (WPPC) and wind farm flow control (WFFC). WPPC is concerned with the connection to the power system, compliance with grid codes, and provision of power system services. This comprises the traditional way of operating a WF without consideration of aerodynamic turbine interaction. However, flow phenomena like wake effects can have a large impact on the overall performance of the WF. WFFC considers such aerodynamic phenomena in the WF operation. It can be viewed as a new feature that shall be integrated with the existing control functions. The interaction of these different control concepts is discussed in this article, leading to an identification of the challenges whose solutions will contribute to a successful integration of electrical system and aerodynamic aspects of WF control

Towards integrated wind farm control: Interfacing farm flow and power plant controls

Concepts for control of wind farms (WFs) can be clustered into two distinct concepts, namely, wind power plant control (WPPC) and wind farm flow control (WFFC). WPPC is concerned with the connection to the power system, compliance with grid codes, and provision of power system services. This comprises the traditional way of operating a WF without consideration of aerodynamic turbine interaction. However, flow phenomena like wake effects can have a large impact on the overall performance of the WF. WFFC considers such aerodynamic phenomena in the WF operation. It can be viewed as a new feature that shall be integrated with the existing control functions. The interaction of these different control concepts is discussed in this article, leading to an identification of the challenges whose solutions will contribute to a successful integration of electrical system and aerodynamic aspects of WF control.Towards integrated wind farm control: Interfacing farm flow and power plant controlspublishedVersio