![]() 1.1 Determination of loads based on the velocity fieldĪ good example of a non-direct measurement approach is a well-established experimental technique for the determination of aerofoil profile drag from the momentum deficit in the wake described by Betz ( 1925). Therefore, the literature review shows numerous studies in which the aerodynamic loads are derived from the flow-field information. However, it is obvious that there exists a physical link between the flow behaviour and the body forces generation mechanism. force balance measurements vs pressure probe measurements). A common experimental research practice is to use separate techniques for aerodynamic force and flow measurements (e.g. In experimental fluid dynamics, the investigations of aerodynamic loads apart from measurements of flow field quantities such as velocity, pressure, and temperature are of special interest. It is evidently necessary to carry out research on aerofoils as they are used extensively in many engineering applications such as aircraft wings, wind turbine blades, bridge decks, towers. Slender, aerofoil-shaped bodies exposed to the flow have been an object of experimental studies since the beginning of aerodynamic investigations that started more than a hundred years ago. In the case of drag estimation, an acceptable level of similarity was observed (max. An exceptional agreement between the experimental and reference numerical lift characteristics was attained (relative differences no larger than 5%). Lift and drag coefficient characteristics as a function of the angle of attack were obtained. A flow around the standard NACA0012 aerofoil at two flow regimes was investigated (Re= \(0.7\times 10^5\) and Re= \(1.4\times 10^5\)). The developed method was tested and verified with the reference computational fluid dynamics simulation results and applied further to the wind tunnel experimental data. Additionally, pressure field reconstruction based on velocity data, which enabled an application of small control surfaces and kept the drag estimation error at a satisfactorily low level, was introduced. The momentum deficit, within a given control volume containing the analysed aerofoil, is determined and related to the reaction drag force exerted on the body. In the case of the drag force estimation, an analysis of fluid momentum changes has been used. An essential achievement made is the development of a procedure for finding an optimal size of the integration curve used for lift calculations. It is obtained by integrating the velocity field along a closed-loop encircling the body. Determination of the lift force is based on velocity circulation calculations. Fundamental fluid mechanics theories were employed to develop algorithms for load estimation. Therefore, PIV results provide sufficient input experimental data to be used. It is shown that the only information needed to estimate the lift and drag forces exerted on a body placed in the flow is a velocity distribution measured around the investigated object. As PIV is an optical measurement technique, the developed method for load determination can be defined as noninvasive. It is based on velocity vector field results obtained with Particle Image Velocimetry (PIV). Furthermore, it enables the cruise performance and drag divergence Mach number to be predicted with only one simulation of the cruise point, which will greatly save the computational cost of optimizations.An experimental method for determination of aerodynamic loads is presented. It indicates that the drag divergence Mach number can be increased by obtaining a shock wave that is further upstream in the detailed design. Compared with Korn's equation, the discovered correlation reduces the maximum prediction error by approximately 40%. A new linear correlation is discovered and validated by existed airfoil databases. Correlation screening and multivariate regression are carried out to discover knowledge about the airfoil drag divergence Mach number and pressure distribution features. This paper designs a supercritical airfoil database that covers the typical free stream Mach number, angle of attack, lift coefficient, and geometry of modern transonic commercial aircraft. However, it neither reveals the key factors of fluid features on the drag divergence nor contributes to the detailed design. It is very helpful in the aircraft initial design. For example, Korn's equation predicts the airfoil drag divergence Mach number using the airfoil maximum thickness and the lift coefficient. Aerodynamic rules and knowledge are often obtained through theoretical research and experiments, which have contributed greatly to aircraft design. ![]()
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