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See detailNumerical and Experimental Investigation of Slot-Blown Air Over a Cylinder
Runge, W.; Buysschaert, F.; Hayez, J.; Carlier, F.; Antoine, H.; Dimitriadis, Grigorios; Degrez, G.

in Knight, L.; Lipatov, I.; Reijasse, P. (Eds.) Progress in Flight Physics - Volume 7 (2015)

The paper investigates the concept of directional control of helicopters without tail rotor by means of the Coanda effect. Slot-blowing around a cylinder in a steady flow is modeled computationally, using the unsteady k-ω shear stress transport (SST) solver in NUMECA, as well as experimentally in the wind tunnel of the Université de Liège. While the concept, in general, is promising, it is shown that there are some potential problems, including pitch yaw coupling and some unsteady flow conditions. These problems exist under various circumstances and are due, at least, in part, to the complicated flow-field that governs this problem, even in two dimensions.

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See detailFlow Visualization and Proper Orthogonal Decomposition of Aeroelastic Phenomena
Andrianne, Thomas; Norizham, Abdul Razak; Dimitriadis, Grigorios

in Okamoto, Satoru (Ed.) Wind Tunnels (2011)

The modal decomposition of unsteady flowfields was proposed in the 1990s by several authors. Proper Orthogonal Decomposition (POD) is one method that can be used in order to perform this modal decomposition; it became popular for aerodynamics research in the 2000s, although it was first proposed for use in fluid dynamics in the 1960s. The objective of the present work is to expand the methodology of the application of POD to experimental flowfields. There are two aspects to this expansion: 1. Allow the models to oscillate. The source of the unsteadiness will then be the movement of the model, as well as any unsteadiness due to flow separation. 2. Study the interaction between the different sources of unsteadiness. In particular observe how the modes generated by one source of unsteadiness interact with the modes generated by the other. Determine if it is possible to separate the structural from the aerodynamic sources of unsteadiness.

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See detailGust Loads
Dimitriadis, Grigorios

in Multiple (Ed.) Design Loads for Future Aircraft (2002)

The selection of design loads and requirements is defining the structural weight of airplanes and their safety. Therefore the definition of requirements should be performed very critically by the customer and structural weight should be assessed based on sensitivity analysis of the total aircraft which includes flight manoeuvre simulation, flight control system, aerodynamics and elastic effects introduced by finite elements. To produce these analyses is the job of the aircraft companies. After selection of most load critical flight manoeuvres (pull up manoeuvres, initiation of roll manoeuvres etc.) the calculation of airloads and inertia loads must include the flight control system and its failure cases because it affects the motion of the control surfaces and therefore the aircraft. With the advent of carbon fibre composite structures discrete loads are the predominant limiting design conditions but it should be emphasised that most structures are of a hybrid nature with metal frame which are still susceptible to fatigue loads. For airplanes designed to civil requirements such as transport airplanes, tankers etc. the definition of continuous turbulence and inclusion of FCS failure cases and nonlinearities such as control surface angles is extremely important. There was a long way from load assumptions used by the Wright Brothers who designed their Flyer to a 5g limit to the load limiting capabilities of the care free handling flight control system of the Eurofighter. Also the US-Airforce Mil-Specifications which were used to design NATO airplanes such as Tornado, F16 and F18 in the 1970’s are obsolete today and the MIL-A-87221 (USAF) is only a frame without the essential quantitative material. All these issues are addressed in this manual including comparisons of regulations and descriptions of new specifications. Complete procedures how to establish design loads are presented which should help for the design of new airplanes. The importance of dynamic phenomena which produce design loads for various aircraft parts such as intakes, leading edges etc. is also highlighted. Loads monitoring systems are necessary to prove calculated loads and monitor fatigue loads to establish the remaining structural life. There is a description of a modern system. For transport type aircraft gust load cases are the most critical for strength design and they are also the main fatigue loading source for the major part of the structure. Methods for discrete and continuous gust loading cases are presented together with nonlinear example calculations. In the appendix there is a description of failure cases and their effect on loads for transport aircraft and a specification of a landing gear which could be used as an example how to specify the whole structure as a system. The military use of this manual is to establish procedures to build the lightest structure for the military requirements. Agreement on requirements and design loads within the NATO countries could standardise pilot training, aircraft usage, increase aircraft life and reduce maintenance. Since the search of the best usage of the aircraft for its military purpose will continue to integrate structure and avionics such as fire and flight control systems as an example there will be a continuous need for future work.