Multi-element Airfoil Configurations Research Articles

Investigating the Performance of a Novel Multi-Element Airfoil Concept Using Numerical Analysis

Separation control is one of the trending topics recently for Vertical Axis Wind Turbine (VAWT) applications, flow separation that occur on the suction side of an airfoil is a major limitation for VAWTs starting and power coefficient; passive control of flow separation has been attracting wind energy research community recently. The principle objective of this paper is to investigate the effect of the multi-element airfoil on the aerodynamic characteristics at wide range of angles of attack at a Reynolds number of 140,000. The multi element airfoil modification has been implemented by replacing the baseline airfoil with two airfoil members within the same geometrical profile of the original baseline airfoil, cambered and symmetrical airfoil members were investigated in this work. The cambered airfoil sections were made of the NACA 4412 airfoil while the symmetrical airfoil sections consisted of the NACA 0015 airfoil. The baseline airfoil is a profile of NACA 0021. The numerical investigation was executed using computational fluid dynamics (CFD) by the usage of ANSYS FLUENT and the turbulence model used was the k-ε Standard. The results of the present research show that the optimized multi-element airfoil configurations have better performance than the baseline airfoil at high angles of attack. A significant delay of separation was observed using the multi element airfoil, resulted in an increase of 200% in the glide ratio using cambered airfoil members and of 100% using symmetric airfoil members. These results are expected to have a significant effect on the performance of low wind speed wind turbines. In addition, a potential benefit for vertical axis wind turbines, whereas the airfoil generates lift at wider range of angles of attack.

Multi-element airfoil configuration for HAWT: A novel slot design for improved aerodynamic performance

Wind energy has a vast potential to provide low-carbon energy in the future. However, to improve the wind turbine blade efficiency, longer blades are being manufactured, which causes expensive production, complicated logistics and structural instability. For good structural integrity, the root airfoils are kept thicker, which brings unsteady aerodynamic characteristics to the inboard region of the blade. Therefore, multi-element airfoil configuration is introduced. In the present study, DU-99-W-405 airfoil is chosen, and a 2D CFD analysis is performed using ANSYS Fluent. Novel slot design shows the increment in lift coefficient with the angle of attack, which helped delay the stall.

Parameter assessment for virtual Stackelberg game in aerodynamic shape optimization

In this paper, parametric studies of virtual Stackelberg game (VSG) are conducted to assess the impact of critical parameters on aerodynamic shape optimization, including design cycle, split of design variables and role assignment. Typical numerical cases, including the inverse design and drag reduction design of airfoil, have been carried out. The numerical results confirm the effectiveness and efficiency of VSG. Furthermore, the most significant parameters are identified, e.g. the increase of design cycle can improve the optimization results but it will also add computational burden. These studies will maximize the productivity of the effort in aerodynamic optimization for more complicated engineering problems, such as the multi-element airfoil and wing-body configurations.

Analysis of Multi-Element Airfoil Configurations: A Numerical Approach

Multi element airfoils are high lift devices and provide improved aerodynamic characteristics which are beneficial for several applications such as aircraft wings wind turbine blades Simulations were performed using the computational panel code developed in MATLAB for the airfoils P N GA W RAF NLR configurations The results were obtained for varying angle of attacks from to deg to include the effects of turbulence The lift and drag coefficients are evaluated for the airfoil configurations P N for Reynolds number range of x x The velocity and pressure contours distributions are illustrated to predict the laminar to turbulent flow characteristics on the airfoil surface The maximum lift coefficient for single slotted flap element is found to decrease for large angle of attack beyond the stall region and for slat element the increase in lift is found to be marginal at high angle of attack The maximum lift coefficient obtained including flap and slat elements is and the drag coefficient is

Analysis of Multi-Element Airfoil Configurations: A Numerical Approach

Multi element airfoils are high lift devices and provide improved aerodynamic characteristics which are beneficial for several applications such as aircraft wings wind turbine blades Simulations were performed using the computational panel code developed in MATLAB for the airfoils P N GA W RAF NLR configurations The results were obtained for varying angle of attacks from to deg to include the effects of turbulence The lift and drag coefficients are evaluated for the airfoil configurations P N for Reynolds number range of x x The velocity and pressure contours distributions are illustrated to predict the laminar to turbulent flow characteristics on the airfoil surface The maximum lift coefficient for single slotted flap element is found to decrease for large angle of attack beyond the stall region and for slat element the increase in lift is found to be marginal at high angle of attack The maximum lift coefficient obtained including flap and slat elements is and the drag coefficient is

Reordering of hybrid unstructured grids for an implicit Navier-Stokes solver based on OpenMP parallelization

Grid reordering is an efficient way to obtain better implicit convergence speed in viscous flow simulation based on unstructured grids. When performing parallel computation on the shared memory machines, the convergence performance for solving high-Reynolds number flow with LU-SGS implicit scheme is ruined by the interface between different sub-domains divided by OpenMP parallelization. In order to improve the compatibility between OpenMP parallel environment and the implicit LU-SGS time-stepping scheme, a grid reordering method for unstructured hybrid grids is proposed. In this method, the structured-grid cells in the viscous layer near-body surface are reordered along the normal direction (like columns) and the unstructured part is reordered layer by layer according to the neighboring relations. To investigate the performance of the current implementation, turbulent flows around the RAE2822 airfoil, the NHLP-2D L1T2 multi-element airfoil configuration, the DLR-F6 wing–body–nacelle–pylon configuration and an aerospace plane has been simulated on unstructured hybrid grids. The numerical results show that the grid reordering method is an efficient and practical strategy for improving the convergence rate and the overall efficiency in the parallel computation with unstructured flow solver.

Effect of Three-Dimensional Shear-Layer Structures on Slat Cove Unsteadiness

Numerical simulations are used to investigate the local and global dynamics of large-scale, three-dimensional vorticity structures within the free shear layer originating from the slat cusp of a multielement airfoil configuration. Results indicate that accounting for the local three-dimensionality of flow fluctuations leads to substantially improved agreement between the computed unsteady near-field solution and wind tunnel measurements based on particle image velocimetry. Analysis of simulation data indicates the potential significance of high intensity turbulent fluctuations near the reattachment location along the slat lower surface toward the generation of broadband slat noise. The computed acoustic characteristics, in terms of the frequency spectrum and spatial distribution within short distances from the slat, resemble the previously reported, subscale measurements of slat noise.

Multipoint and Multi-Objective Aerodynamic Shape Optimization

A Newton‐Krylov algorithm is presented for the aerodynamic optimization of singleand multi-element airfoil configurations. The flow is governed by the compressible Navier‐Stokes equations in conjunction with a one-equation turbulence model. The preconditioned generalized minimum residual method is applied to solve the discreteadjoint equation, leading to a fast computation of accurate objective function gradients. Optimization constraints are enforced through a penalty formulation, and the resulting unconstrained problem is solved via a quasi-Newton method. Design examples include lift-enhancement and multi-point lift-constrained drag minimization problems. Furthermore, the new algorithm is used to compute a Pareto front for a multi-objective problem, and the results are validated using a genetic algorithm. Overall, the new algorithm provides an ecient and robust approach for addressing the issues of complex aerodynamic

Transitional Flow Modeling and Application to High-Lift Multi-Element Airfoil Configurations

To enhance its capabilities to handle e ows with transition, a Reynolds averaged Navier ‐Stokes solver has been extended with regard to the modeling of transitional e ow regions based on transition length models and the intermittency function. Because the full coupling of the solver to an e N -method that predicts the locations of transitiononsethasnotyetbeencompleted,thepointsoflaminarseparationaresupposedtorepresentthetransition locations in a e rst step. A method and an algorithm for detecting the laminar separation points are derived, and the intermittency function and two transition length models are implemented and validated for a selected high-lift multi-element test case. The background of the implementation work and the testing of the functionalities of the algorithms are focused on. Details of the implementation, which are consequences of an underlying transition prediction strategy, are outlined. The testing is described and then documented. Nomenclature cd = drag coefe cient c f = skin-friction coefe cient cl = lift coefe cient cp = pressure coefe cient FLGlt = laminar‐ turbulent e ag for the code internal eddy

On Modeling of Transitional Flow and its Application to a High Lift Multi-element Airfoil Configuration

In order to enhance its capabilities to handle flows with transition a RANS solver has been extended with regard to the modeling of transitional flow regions based on transition length models and the intermittency function. As the full coupling of the solver to an e*-method that predicts the locations of transition onset has not yet been completed the points of laminar separation are supposed to represent the transition locations in a first step. A method and an algorithm for detecting the laminar separation points are derived, the intermittency function and two transition length models are implemented and validated at a selected high lift multi-element test case. The paper focuses on the background of the implementation work and the testing of the functionalilites of the algorithms. Details of the implementation, which are consequences of an underlying transition prediction strategy are outlined. The testing is described and documented by a number of commented plots.

Bubble Bursting and Laminar Separation Unsteadiness on a Multi-Element High Lift Configuration

The purpose of this work is to gain insight into the problem of the bursting of a laminar separation bubble in the nose region of a slotted flap on a multi-element airfoil configuration. The interest in bubble bursting, which, especially on multi-element configurations has not been thoroughly investigated yet, was raised by the experimental results obtained while testing a computer designed flap in the low speed low Turbulence wind tunnel of the Delft University of Technology. A sudden and dangerous stall was found to occur on the flap surface due to the bursting of a bubble in its nose region. CFD calculations, both laminar and RANS, were first performed on a single element configuration, namely the Eppler E387 airfoil (Re = 105) and then on the multi-element configuration tested in the wind tunnel (Re = 2 ·106). The results show that a strong vortex shedding can potentially originate from the separated shear layer, both on the flap and on the single element airfoil, suggesting a close connection between the two cases. The effect of transition on the structure of the bubble was investigated by imposing and then varying the transition point. The computational results suggest that the unsteady behavior of the laminar bubble has to be regarded as a major issue in order to find an effective bursting predictor method for airfoil design.

Prediction of High-Lift Flows Using Turbulent Closure Models

The flow over two different multi-element airfoil configurations is computed using linear eddy viscosity turbulence models and a nonlinear explicit algebraic stress model. A subset of recently-measured transition locations using hot film on a McDonnell Douglas configuration is presented, and the effect of transition location on the computed solutions is explored. Deficiencies in wake profile computations are found to be attributable in large part to poor boundary layer prediction on the generating element, and not necessarily inadequate turbulence modeling in the wake. Using measured transition locations for the main element improves the prediction of its boundary layer thickness, skin friction, and wake profile shape. However, using measured transition locations on the slat still yields poor slat wake predictions. The computation of the slat flow field represents a key roadblock to successful predictions of multi-element flows. In general, the nonlinear explicit algebraic stress turbulence model gives very similar results to the linear eddy viscosity models.

Navier-Stokes computations and experimental comparisons for multielement airfoil configurations

Navier-Stokes computations and experimental comparisons for multielement airfoil configurations

Compressible Navier-Stokes computations of multielement airfoil flows using multiblock grids

Numerical solutions of the compressible thin-layer Navier-Stokes equations are presented for high-lift multielement airfoil configurations. Multiblock grids are used, allowing straightforward implementation of an approximately factored implicit algorithm. Interfaces between blocks are treated by overlapping the grids and taking one layer of points from neighboring blocks. Turbulence is modeled using the Baldwin-Earth one-equation turbulence model. High-lift applications presented for comparison with wind tunnel data include: an NACA 4412 airfoil with NACA 4415 flap, a GA(W)-1 airfoil with a 29% chord flap at 30-deg flap angle and two gap settings, and a GA(W)-1 airfoil with 15% chord slat and 29% chord flap. Good agreement with experimental data is obtained for cases with fully attached flow or small regions of separated flow. For cases with extensive regions of flow separation, the thickness and extent of the separated regions are underpredicted.

Implicit Solvers for Unstructured Meshes

Implicit methods are developed and tested for unstructured mesh computations. The methods are used to solve the compressible Navier-Stokes equations to steady state. The approximate system which arises from the Newton linearization of the nonlinear evolution operator is solved by using the preconditioned GMRES (generalized minimum residual) technique. Three different preconditioners, namely, the incomplete LU factorization (ILU), block diagonal factorization, and the symmetric successive over-relaxation (SSOR) are investigated. The preconditioners have been optimized to have good vectorization properties. SSOR and ILU themselves are studied as iterative schemes. The various methods are compared over a wide range of problems. Ordering of the unknowns, which affects the convergence of these sparse matrix iterative methods, is also investigated. Results are presented for inviscid and turbulent viscous calculations on single and multi-element airfoil configurations using globally and adaptively generated meshes.

Multiblock mesh generation for multiple element airfoils with Euler solutions

A novel search algorithm for the decomposition of arbitrary, two-dimensional domains into non-overlapping, topologically rectangular blocks is described. The algorithm automates several stages in the domain decomposition and grid generation process in two dimensions. To demonstrate the technique, solutions to the Euler equations for several multi-element airfoil configurations are presented.