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Innovative Methods of Separated Flow Control in Aeronautics

Final Report Summary - IMESCON (Innovative Methods of Separated Flow Control in Aeronautics)

IMESCON (Innovative Methods of Separated Flow Control in Aeronautics) was a high quality training network which trained 13 well qualified researchers in the area of active flow control and new helicopter technology. 8 Early Stage Researchers developed their PhD Theses. Implemented training programme of early stage and experienced researchers from industry and academia combined expertise from fluid dynamics, composite material, Micro Electro Mechanical Systems (MEMS), experimental techniques and numerical modelling of coupled multiple simultaneous physical phenomena. Major project objective was transfer of knowledge in the highly multidisciplinary filed of flow control and development of an innovative approach for coupled multi physics co-simulation, testing and optimization of active flow separation control systems applied in the aerospace industry.
The reference helicopter rotor data was provided by PZL Swidnik constituted the common platform for the entire project to work on the same research object.
The progress beyond state of the art achieved by the project research effort was achieved in the area of the flow control methods. It was proven that the rod vortex generators in channel flows are able to successfully control the separation of the flow thus reducing drag and increasing lift. Sophisticated and validated comprehensive simulation activity proven the application of this technology to the existing helicopter main rotor blades increase the thrust with a minimal power consumption penalty in hoover and forward flight. This activity also required development and use of the numerical codes coupling for the overall system analysis.
It has been proven that the numerical model implemented in FLOWer code is able to reproduce the main features measured in the experiments for the clean case. The appearance of flow separation suggested the possibility of application of a flow control device for improving the aerodynamic performance of the rotor. The numerical results related to the implementation of rod vortex generators on hovering helicopter rotor blades confirm that this method of passive control reduces the flow separation increasing thrust over power consumption.
In this work the use of a Gurney flap was put forward as a means to improve the hover performance of a W3 Sokol helicopter rotor, and alleviate possible dynamic stall during forward flight. The maximum FM of the blade did not improve, but at high thrust settings it was enhanced by 6% over the performance of the clean blade. The effect of the Gurney flap to pitch the nose of the section down was evaluated with aeroelastic calculations and it was found that the extra lift of the Gurney in combination with the extra blade twist resulted in an increased FM. Among different sizes of Gurney the one of 2% of the chord was the most effective. The location of the Gurney flap was restricted by the existence of the trim tab and the trailing edge tab. Moreover the influence of the span of the flap was tested by increasing the Gurney span by 10% at each side, which did not seem to improve the performance of the blade significantly. In forward flight, dynamic stall phenomenon was captured at the retreating side of the rotor at extreme flight conditions (Mass=6400 Kg, μ=0.33). The flow was separated between r/R= 0.40 and r/R= 0.60 at azimuth between 220deg and 310deg. As a result, the Gurney flap which will be used next for the CFD computations of the W3 rotor in forward flight was deployed in the according schedule presented above and the size of it will remain at 2% of the chord. As expected the rotor with the active gurney resulted in higher thrust than the clean rotor which led to the increase of the separated flow. As a result, first the rotor with the gurney was trimmed at a same thrust value of CT = 0.008.
The aerodynamic coefficients obtained for a clean NACA 23012 airfoil show reasonable agreement with the results given in IMESCON Design reference helicopter rotor data The effect of Gurney flap is evident from the increased lift coefficient than a clean airfoil, although the airfoil stalls at much lower angle of attack with considerable increase in drag coefficient thereafter, negating the advantages from the Gurney flap at higher angle of attacks.
Research effort within Novel actuator and adaptive control techniques which is the focal point of the WP3 was accounting for Non-linear model based control technique and Iterative Learning control techniques for multi-variable systems complemented by Fiber optic and PZT sensing techniques from WP2. The research on PZTs sensors and its application was focused on determination of adequate PZTs properties (dimensions, type of material) to satisfy the input signal demands of the control and SHM systems. In parallel the research on fibre optics pressure, strain and vibration acceleration sensors application was realized. In the static and dynamic tests of the blade instrumented with different types of transducers comparing strain readings from optical vs. electric sensor.
The experiments performed with the SMART Layers proved the good capability of this technology to detect small defects, up to 0.1% of the total mass of the structure, for isotropic materials.
The best diagnostic frequency for the Al plate was found to be 100 kHz. Although higher frequencies are desired because offer the possibility to detect smaller damage, for the Al plate at frequencies above 300 kHz the S0 mode amplitude reached the one of the A0 mode, the one used in the damage detection procedure, thus the interference between the two destroyed the information about damage coming from reflections.
This work presented the research activities in development, simulation and validation of mechatronic models for complex mechatronic systems such as the considered machine tool. A flexible multi-body model and a 1D lumped parameter model together with the controller are developed. A co-simulation is set up between these models.
It is shown that unlike 1D lumped modeling approach, the flexible multi-body approach allows us to model the elastic deformation behavior of the system (i.e. gantry and tool attachment bracket). In addition, it is observed that the dynamic characteristics of the machine are dependent on the spatial position of the machine head. The model can also be used to forecast the influence of specific design changes, and to assess the impact of different control architectures. Consequently, the manufacturers of mechatronic system can reduce time to market while meeting with market demands.
An alternative strategy to generate the drive signal for service load simulation was developed. The competitive advantages of the proposed strategy over existing state of the art TWR process include: (i) online strategy with increased automation, (ii) decreased workload for the test rig operator, (iii) improved tracking accuracy and (iv) better convergence properties for the system with uncertainties and non-linearities. Moreover, the method is computationally very feasible to implement in real-time irrespective of the length of the signal or time horizon because the learning algorithm is based on the truncated impulse response of the system. The proposed method can be used for the systems with minimum phase zeros, non-minimum phase zeros or/and delays.
Finally IMECON project has produced the active flow control system mockup. The model of the section of the W-3 Sokol helicopter blade was equipped with the active Gurney flap driven by the piezoelectric actuators. The mockup integrates research outcomes incorporating, flow, structure, control and actuators into one overall operational system.