Accurate modelling of wind turbine wakes is critical for optimizing wind farm performance, but the complexity of wake interactions poses significant challenges. This study presents a two-phase blind test campaign, part of the Horizon Europe TWEET-IE project, designed to benchmark numerical models and investigate wake control strategies using wind tunnel experiments. Conducted with tandem wind turbine models at the Technical University of Munich and the National Technical University of Athens, the tests include inflow, load, power, and wake velocity measurements under controlled conditions. Phase I serves as an open-data benchmarking exercise for a baseline scenario without wake control, while Phase II introduces active individual blade pitch control to the upstream turbine, challenging participants to simulate advanced wake dynamics. This paper reviews Phase I results and details the experimental framework for Phase II, providing a foundation for advancing wake modelling and control in wind energy research.

Wind turbine wake and modelling is crucial to optimizing future wind farm layouts and hence reducing the cost of energy. This paper presents the first phase of a blind test on modelling controlled and uncontrolled wind turbine wakes. The blind test is based on wind tunnel experiments of two model scale wind turbines (D = 1.1 m) one downstream of the other. The exercise is split into two phases and the first one is presented here, where participants are invited to simulate the baseline case, in which both turbines are aligned with the flow and there is no control on the either turbine. The objective of this phase is to ensure all participants can benchmark their numerical approach against a baseline open data set, where no wake control is applied. Experimental measurements include inflow velocity, turbine power and loads for a range of tip speed ratios. In the second phase, not presented here, the wake of the upstream turbine will be controlled and the performance of the downstream one will be recorded. This will be a blind test with the data not released prior to submissions. The present paper gives an overview of the initial, open benchmark case, including its objectives, methodology and experimental results.

As an alternative to conventional wind turbines, this study considered kites with onboard wind turbines driven by a high airspeed due to crosswind flight (“drag power”). The hypothesis of this study was, that if the kite's lift coefficient is maximized, then the power, energy yield, allowed costs and profit margin are also maximized. This hypothesis was confirmed based on a kite power system model extended from Loyd's model. The performance of small-scale and utility-scale kites in monoplane and biplane configurations were examined for increasing lift coefficients. Moreover, several parameters of the utility-scale system were optimized with a genetic algorithm. With an optimal lift coefficient of 4.5, the biplane outperformed the monoplane. A 40 m wing span kite was expected to achieve a rated power of about 4.1 MW with a power density of about 52 kW/m2. A parameter sensitivity analysis of the optimized design was performed. Moreover, to demonstrate the feasibility of very high lift coefficients and the validity of a utilized simplified airfoil polar model, CFDs of a proposed high-lift multi-element airfoil were performed and the airfoil polars were recorded. Finally, a planform design of a biplane kite was proposed.

This study considers kites with onboard wind turbines driven by a high airspeed due to crosswind flight (“drag powerž [1, 2]). An optimal power curve and an optimal overall power plant design with requirements for a detailed kite design are derived. For that, the model of [3], which extents Loyd’s model by an airfoil polar model, a 3D wing model, a tether drag model, a wind field model and an economics model, is further extended by a model for the electrical cables of the tether and their sizing, an actuator disk model for the rotors for crosswind flight in turbine and propeller mode aswell as for hovering, and a drivetrain model (efficiencies, masses, costs). A biplane kite with a very high lift multi-element airfoil is considered, as it is found as optimal in [3]. The power curve with all meaningful regions and required actuations (rotor drag coefficient/induction factor, lift coefficient, actuated drag via air brakes or sideslipping) is derived. With a genetic algorithm, all free design parameters are optimized and numerous parameter studies are performed. One result is that a 40mwingspan biplane kite with a wing area of 80m2, a lift coefficient of 4 and a tether length of 370machieves a nominal electrical power of 7 MW, i.e. it has a power density of 90kW/ 2. Moreover, the kite power plant has a maximum allowed cost of 5.5 Mio.USD to achieve a LCOE of 0.05 USD/kWh and the kite has a maximum allowed wing mass density of 140 kg/m2. A biplane kite is expected to be superior to a monoplane kite with respect to its ability to sustain the very high wing loading of 1600 kg/m2 caused by the high lift coefficient. First simple component verifications have been conducted, but further verifications are planned for both, component level and systemlevel. In this talk, the derivation and underlying assumptions of the kite model are presented and key results of the parameter studies are discussed.