Double-multiple streamtube model for Darrieus in turbines

An analytical model is proposed for calculating the rotor performance and aerodynamic blade forces for Darrieus wind turbines with curved blades. The method of analysis uses a multiple-streamtube model, divided into two parts: one modeling the upstream half-cycle of the rotor and the other, the downstream half-cycle. The upwind and downwind components of the induced velocities at each level of the rotor were obtained using the principle of two actuator disks in tandem. Variation of the induced velocities in the two parts of the rotor produces larger forces in the upstream zone and smaller forces in the downstream zone. Comparisons of the overall rotor performance with previous methods and field test data show the important improvement obtained with the present model. The calculations were made using the computer code CARDAA developed at IREQ. The double-multiple streamtube model presented has two major advantages: it requires a much shorter computer time than the three-dimensional vortex model and is more accurate than multiple-streamtube model in predicting the aerodynamic blade loads

Numerical Correlations for Heat Transfer From an Array of Hot-Air Jets Impinging on a 3D Concave Surface

The paper presents numerical heat-transfer correlations established from numerical CFD study of a 3D hotair jet array impinging on curved (circular) surface. The results are in the form of numerical correlations for the average and maximum Nusselt number for different nozzle-to-nozzle spacing, nozzle-to-surface height and hot-air jet mach numbers typical of those in an hot-air anti-icing system employed on aircraft wings. The paper presents a validation case and show that the results obtained from the CFD study are in good agreement with experimental data found in literature. The paper presents an interpolation technique, the dual Kriging method, that make use of the numerical database for anti-icing simulation on aircraft wings. The benefit of using the dual Kriging method is that it preserves the non-linear nature of the heat-transfer distribution from a hot-air jet impinging on a curved surface

An Iterative Inverse Design Method Based on Aerodynamic Streamline Equations

Aerodynamic characteristics are very sensitive to airfoil leading-edge geometry, and its accurate treatment is a limitation of many existing design methods. The objective of the present research is to develop an interactive inverse design method that is not only efficient but can also treat the leading-edge region accurately. In the formulation of the method, a small-perturbation geometric equation is deduced from the streamline momentum equations, the continuity equation, and the isentropic relations with the geometry similarity assumption of near streamlines to the airfoil surface. Moreover, the transonic correction is considered in the aforementioned equation with the assumption for the effects of waves reflected from the free surface (sonic line) because the method based on the surface flow values cannot take into account the transonic characteristics such as wave interference. The geometric perturbation normal to the airfoil surface is then calculated by solving this second-order initial value ordinary differential equation iteratively to obtain an airfoil design. Techniques such as airfoil smoothing, nonuniform relaxation, and the strained coordinate transfer are employed to accelerate convergence. The airfoil design cases demonstrate the remarkable efficiency and accuracy of the method not only for compressible flows but also for low-speed flows. Moreover, the method allows the leading-edge shape to be determined accurately and, thus, to overcome the deficiency of many of the related methods

Numerical Correlations for Heat Transfer From an Array of Hot-Air Jets Impinging on a 3D Concave Surface

The paper presents numerical heat-transfer correlations established from numerical CFD study of a 3D hotair jet array impinging on curved (circular) surface. The results are in the form of numerical correlations for the average and maximum Nusselt number for different nozzle-to-nozzle spacing, nozzle-to-surface height and hot-air jet mach numbers typical of those in an hot-air anti-icing system employed on aircraft wings. The paper presents a validation case and show that the results obtained from the CFD study are in good agreement with experimental data found in literature. The paper presents an interpolation technique, the dual Kriging method, that make use of the numerical database for anti-icing simulation on aircraft wings. The benefit of using the dual Kriging method is that it preserves the non-linear nature of the heat-transfer distribution from a hot-air jet impinging on a curved surface

Coriolis Effect on Dynamic Stall in a Vertical Axis Wind Turbine at Moderate Reynolds Number

The immersed boundary method is used to simulate the flow around a two-dimensional rotating NACA 0018 airfoil at sub-scale Reynolds number in order to investigate the separated flow occurring on a vertical-axis wind turbine. The influence of dynamic stall on the forces is characterized as a function of tip-speed ratio. The influence of the Coriolis effect is also investigated by comparing the rotating airfoil to one undergoing a equivalent planar motion, which is composed of surging and pitching motions that produce an equivalent speed and angle-of-attack variation over the cycle. When the angle of attack of a rotating airfoil starts to decrease in the upwind half cycle, the Coriolis force leads to a wake-capturing phenomenon of a vortex pair at low tip-speed ratio. This effects occurs at a slightly different phase in each cycle and leads to a significant decrease in the average lift during the downstroke phase. Moreover, the wake-capturing is only observed when the combination of surging, pitching, and Coriolis force are present. Finally, an actuator model is placed at an appropriate location on the suction side of the airfoil surface to control the wake-capturing phenomenon. Based on preliminary simulations, a momentum coefficient above 0.02 was able to increase the average lift by more than 70% over the upwind-half cycle

Comparison of aerodynamic models for Vertical Axis Wind Turbines

Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple streamtube model, a double-multiple streamtube model, the actuator cylinder model, a 2D potential flow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models, which explicitly model the wake as a system of vorticity, show mostly differences due to the instantaneous or time averaged formulation of the loading and flow, for which further research is needed.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin

Méthode indicielle pour le calcul du décrochage dynamique

Description du décrochage dynamique -- Fonction indicielle -- Modèle indiciel pour l'écoulement potentiel -- Modèle numérique pour l'écoulement potentiel -- Modélisation des effets de non-linearite -- Modélisation du décrochage dynamique profond

Dynamic stall study for the Darrieus rotor

Dynamic-stall model -- Geometric parameters of rotors