Periodic Reporting for period 2 - CICLOP (Characterization of the Interaction between wing and CLosely Operating Propeller) Reporting period: 2022-01-01 to 2023-03-31 Summary of the context and overall objectives of the project Scheduled commercial transport volume is continuously growing, representing the global megatrend “Mobility”. The subsequently higher number of aircraft requires new and low energy concepts to achieve the European and goals for sustainable aviation. Distributed (Electric) Propulsion (DP/DEP), is such new technology which opens up the design space and promises significant increase in overall aircraft efficiency while reducing emissions.DEP offers the possibility to split the power necessary for flight among small propulsion units installed e.g. along the span. This results in an increase of dynamic pressure in the propeller slipstream as well as at the trailing wing. As a consequence, the wing affected by the propeller slipstream produces more lift and thus can be reduced in size. Smaller wings lead to weight and drag reduction of the aircraft and hence to fuel saving and reduction of CO2 emissions.A sound and reliable prediction of the aerodynamic effects of DP/DEP and close wing coupling at high-lift based on aerodynamic models and simulation is not state-of-the-art and high fidelity experimental results for model validation were not available before. The overall objective of CICLOP is to close this gap by providing high fidelity experimental data that allow for a leap in aircraft performance due to efficient synergetic use of DP and wing interaction. The most dominant design parameters, driving the sensitivity of positive as well as adverse aerodynamic effects are identified and quantified during the project.For this purpose, in CICLOP a versatile wind tunnel model coupling three propeller drive trains to a wing was designed and built. The assembly is installed in a 2.4m x 2.4m wind tunnel at TUBS. With a chord length of 0.8m and a wingspan of 2.4m it is a large scale experiment. The three propellers in front of the wing have a maximum diameter of 0.6m and are driven by up to 35kW electric motors. The drive trains are completely decoupled from the wing. Since they are on an extra carrier, the nacelles are not connected to the wing. Thus it is possible to change the relative propeller position to the wing easily.This setup made it possible to test various crucial operating parameters using fully independent distributed drives. In addition to different relative propeller positions to the wing, different propeller blades and various operating conditions were tested. From these actions it can be concluded that the propeller position relative to the wing in high-lift configurations is very crucial for both, the lift gain effect but also the efficiency impact on the propeller. Furthermore, it was found that by changing the blade design and thus the propeller slipstream compared to isolated propeller designs, significant drag reductions of the system can be achieved. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far In the beginning of the project prerequisites were created for CICLOP’s experiment to run successfully. Together with all partners, operating points were defined to be tested in the experiment. Two propeller sizes were identified. One propeller set with a diameter of 0.4m and two propeller sets with a diameter of 0.6m were designed and manufactured. In addition to the aerodynamic design, the structural design and the accommodation of the blades also had to be taken into account. As a result of the two sizes, two separate drive trains are necessary, including motors, power electronics, load cells and mountings.After designing and modelling the assembly was manufactured and built. This includes all mechanical hardware such as wing, propeller drives and support structure, as well as the electronic hardware including power electronics, geared motors and the software to control all components. Furthermore, a measurement setup was developed to store all data. Finally, in a test campaign lasting several months, all points of the previously defined test matrix were successfully performed.By changing the relative position very close to the wing and below the leading edge, an increase of the maximum lift of up to 34% could be observed. The propeller efficiency also increases in such cases leading to possible optimal positions found through the experiment. The experimental techniques selected allow quantifying the full temporal mean state of the airfoil flow in terms of flow patterns, pressure distribution and laminar-turbulent transition.Many different configurations were tested during the measurement campaign. In addition to the relative propeller positions and the three different blade designs already mentioned, other operating parameters were varied. On the one hand, the thrust was changed by pitching and thus six thrust levels were performed per blade design, and on the other hand, the flap of the wing was set to three different angles: Clean, Take-Off and Landing. Furthermore, the wind tunnel speed and the propeller rotational speed were also varied. The large number of possible combinations offered by the model was prioritized, so that a total of 188 configurations were tested.Two scientific papers on the project are currently published. One on the setup from reporting period 1:Oldeweme, J., T. Lindner, P. Scholz, and J. Friedrichs. 2022. “Experiment Design for a Distributed Propulsion Configuration at High Lift”. In: DLRK. DOI: 10.25967/570125.And the other on the first measurement results from reporting period 2:Lindner, T. K., J. Oldeweme, P. Scholz, and J. Friedrichs. 2023. “Experimental Propeller Placement Analysis for a Distributed Propulsion Wing Section in High Lift Configuration”. In: AIAA AVIATION 2023 Forum. DOI: 10.2514/6.2023-3539.Further results are in the process of being published. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) The CICLOP project aims to extend the predictability and evaluability of distributed propulsion configurations. Due to its large number of parameter investigations, the project offers the possibility to establish new high-quality measurement data. The results obtained can ultimately provide better predictions for future designs and further limit the parameter space.In this way, the results obtained can be used to identify key design parameters. These findings can be applied to future designs in the European aerospace industry. The identified maximum lift gain of about 34% by shifting the relative propeller position is one of these key parameters. By gradually changing the position, effects in the vertical, horizontal and spanwise directions were identified and quantified. While the vertical and horizontal displacement has a rather large effect on the propeller, the effect of the spanwise displacement is relatively small.Likewise, the propeller design has a significant influence on the system. A change in the outflow characteristic not only affects the efficiency of the propeller, but also the drag on the wing. Another finding that has been quantified is the lift gain on the wing as a function of the thrust generated by the propeller. For the largest measured thrust coefficient, this lift gain is highest at the reference position, up to 37%. In addition to these conclusions, the results show many other details that can be found in the publications.The experimental results show that the effects have been quantified. These findings can now be used by follow-up projects and DEP aircraft designs can be concretized on this basis. CICLOP Test rig concept
