Ion Paraschivoiu

Anti-Icing System Simulation Using CANICE

A mathematical model of a hot air anti-icing system and its implementation in the ice accretion simulation code CANICEarepresented.Theicing codeisusedto predictthesurfacetemperatureandtheamount ofrunbackwater for given atmospheric conditions and heat e ux distribution from an anti-icing device. The external boundary layer is modeled with an integral method. Velocity and temperature distribution in the water e lm are estimated using a polynomial approximation. Conduction in the airfoil skin is taken into account with a one-dimension model. Numerical results are compared with experimental and numerical results from NASA for three different icing conditions. The comparison shows that surface temperatures are very sensitive to the water droplet impingement limits. The integral method used here failed to predict correctly the heat transfer coefe cients in the transition region of the boundary layer. When experimental heat transfer coefe cients are used, the model gives satisfactory results.

Numerical Heat Transfer Correlation for Array of Hot-Air Jets Impinging on 3-Dimensional Concave Surface

Numerical heat transfer correlations established from a numerical computational fluid dynamics (CFD) study of a three-dimensional hot-air jet array impinging on curved (circular) surface are presented. 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 antiicing system employed on aircraft wings. A validation case is presented, and it is shown that the results obtained from the CFD study are in good agreement with experimental data found in the literature. An interpolation technique, the Dual-Kriging method, that makes use of the numerical database for antiicing simulation on aircraft wings is presented. The benefit of using the Dual-Kriging method is that it preserves the nonlinear nature of the heat transfer distribution from a hot-air jet impinging on a curved surface.

An Aerodynamic Method for the Analysis of Isolated Horizontal-Axis Wind Turbines

The aerodynamic analysis of a wind turbine represents a very complex task since it involves an unsteady three-dimensional viscous flow. In most existing performance-analysis methods, wind turbines are considered isolated so that interference effects caused by other rotors or by the site topology are neglected. Studying these effects in order to optimize the arrangement and the positioning of Horizontal-Axis Wind Turbines (HAWTs) on a wind farm is one of the research activities of the Bombardier Aeronautical Chair. As a preliminary step in the progress of this project, a method that includes some of the essential ingredients for the analysis of wind farms has been developed and is presented in the paper. In this proposed method, the flow field around isolated HAWTs is predicted by solving the steady-state, incompressible, two-dimensional axisymmetric Navier-Stokes equations. The turbine is represented by a distribution of momentum sources. The resulting governing equations are solved using a Control-Volume Finite Element Method (CVFEM). This axisymmetric implementation efficiently illustrates the applicability and viability of the proposed methodology, by using a formulation that necessitates a minimum of computer resources. The axisymmetric method produces performance predictions for isolated machines with the same level of accuracy than the well-known momentum-strip theory. It can therefore be considered to be a useful tool for the design of HAWTs. Its main advantage, however, is its capacity to predict the flow in the wake which constitutes one of the essential features needed for the performance predictions of wind farms of dense cluster arrangements.

Appropriate Dynamic-Stall Models for Performance Predictions of VAWTs with NLF Blades

This paper illustrates the relative merits of using Natural Laminar Flow (NLF) airfoils in the design of Vertical Axis Wind Turbines (VAWT). This is achieved by the application of the double-multiple-streamtube model of Paraschivoiu to the performance predictions of VAWTs equipped with conventional and NLF blades. Furthermore, in order to clearly illustrate the potential benefit of reducing the drag, the individual contributions of lift and drag to power are presented. The dynamic-stall phenomena are modelled using the method of Gormont as modified by several researchers. Among the various implementations of this dynamic-stall model available in the literature, the most appropriate and general for NLF applications has been identified through detailed comparisons between predicted performances and experimental data. This selection process is presented in the paper. It has been demonstrated that the use ofNLF airfoils in VAWT applications can lead to significant improvements with respect to conventional design only in a very low wind speed range, the extent of which is negligible with respect to the VAWT operational wind speeds.

Aerodynamic Analysis Models for Vertical-Axis Wind Turbines

This work details the progress made in the development of aerodynamic models for studying Vertical-Axis Wind Turbines (VAWTs) with particular emphasis on the prediction of aerodynamic loads and rotor performance as well as dynamic stall simulations. The paper describes current effort and some important findings using streamtube models, 3-D viscous model, stochastic wind model and numerical simulation of the flow around the turbine blades. Comparison of the analytical results with available experimental data have shown good agreement.

Numerical Simulation of Dynamic Stall Around an Airfoil in Darrieus Motion

The objective of this study is to investigate the two-dimensional unsteady flow around an airfoil undergoing a Darrieus motion in dynamic stall conditions. For this purpose, a numerical solver based on the solution of the Reynolds-averaged Navier-Stokes equations expressed in a streamfunction-vorticity formulation in a non-inertial frame of reference was developed. The governing equations are solved by the streamline upwind Petrov-Galerkin finite element method (FEM). Temporal discretization is achieved by second-order-accurate finite differences. The resulting global matrix system is linearized by the Newton method and solved by the generalized minimum residual method (GMRES) with an incomplete triangular factorization preconditioning (ILU). Turbulence effects are introduced in the solver by an eddy viscosity model. The investigation centers on an evaluation of the algebraic Cebeci-Smith model (CSM) and the nonequilibrium Johnson-King model (JKM). In an effort to predict dynamic stall features on rotating airfoils, first the authors present some testing results concerning the performance of both turbulence models for the flat plate case. Then, computed flow structure together with aerodynamic coefficients for a NACA 0015 airfoil in Darrieus motion under dynamic stall conditions are presented.

A Straight-Bladed Variable-Pitch VAWT Concept for Improved Power Generation

The paper presents three modifications for an improved performance in terms of increased power output of a straight-bladed VAWT by varying its pitch. Modification I examines the performance of a VAWT when the local angle of attack is kept just below the stall value throughout its rotation cycle. Although this modification results in a very significant increase in the power output for higher wind speeds, it requires abrupt changes in the local angle of attack making it physically and mechanically impossible to realize. Modification II improves upon the first by replacing the local angle of attack by the blade static-stall angle only when the former exceeds the latter. This step eliminates the two jumps in the local effective angle of attack curve but at the cost of a slight decrease in the power output. Moreover, it requires a discontinuous angle of attack correction function which may still be practically difficult to implement and also result in an early fatigue. Modification III overcomes the limitation of the second by ensuring a continuous variation in the local angle of attack correction during the rotation cycle through the use of a sinusoidal function. Although the power output obtained by using this modification is less than the two preceding ones, it has the inherent advantage of being practically feasible.Copyright

Heat and mass transfer in the case of anti-icing system simulation

Aircraft manufacturers need anti-icing system simulations to help in the design of ice protection systems. Heat and mass transfer predictions obtained with two different methods to solve the boundary layer in the case of an anti-icing simulation are compared. The integral method and the finite difference method are used to solve the boundary-layer equations, including the mass diffusion equation. The boundary-layer solvers are implemented into the code CANICE, which models the ice accretion process. Comparison of heat and mass transfer distributions and surface temperature distributions are made. Surface temperatures predicted with the finite difference method are closer to experimental results than surface temperatures predicted with the integral method

Low Reynolds Number Vertical Axis Wind Turbine for Mars

A low Reynolds number wind turbine is designed to extract the power from wind energy on Mars. As compared to solar cells, wind turbine systems have an advantage on Mars, as they can continuously produce power during dust storms and at night. The present work specifically addresses the design of a 500 W Darrieus-type straight-bladed vertical-axis wind turbine (S-VAWT) considering the atmospheric conditions on Mars. The thin atmosphere and wind speed on Mars result in low Reynolds numbers (2000–80000) representing either laminar or transitional flow over airfoils, and influences the aerodynamic loads and performance of the airfoils. Therefore a transitional model is used to predict the lift and drag coefficients for transitional flows over airfoils. The transitional models used in the present work combine existing methods for predicting the onset and extent of transition, which are compatible with the Spalart-Allmaras turbulence model. The model is first validated with the experimental predictions reported in the literature for an NACA 0018 airfoil. The wind turbine is designed and optimized by iteratively stepping through the following tasks: rotor height, rotor diameter, chord length, and aerodynamic loads. The CARDAAV code, based on the “Double-Multiple Streamtube” model, is used to determine the performances and optimize the various parameters of the straight-bladed vertical-axis wind turbine.

Prediction of ice accretion with viscous effects on aircraft wings

A method using the viscous-inviscid interaction technique has been developed for the calculation of ice accretion on three-dimensional wings of any cross section or planform geometry.