Multi-element Airfoil Research Articles

Efficient mesh deformation based on Cartesian background mesh

Moving mesh is widely used in the simulation of aerodynamic shape optimization, multibody relative motion, aircraft icing and aeroelasticity. The efficient and high quality mesh deformation is the key technology of moving mesh. This paper presented a new Mesh Deformation method based on Cartesian Background Mesh (MDCBM). First, the Cartesian background mesh is deformed with radial basis functions (RBF). Second, the displacement of Cartesian background mesh is algebraically interpolated onto all meshes in the computing domain. Since the background mesh is coarse, the background mesh deformation can be finished fast. Because the background mesh of MDCBM is regular, the mapping relationship between background mesh and the computing mesh is simple. So the time spent on mapping search is substantially reduced. The examples including NACA0012 airfoil, multi-element airfoil with structured, unstructured mesh and DLR-F4 wing–body show the good performance of MDCBM. We highlight the advantages of MDCBM with respect to its computational efficiency and high quality of deformed mesh.

Adaptive Variable-Fidelity Analysis and Design Using Dynamic Fidelity Indicators

The purpose of the current study is to develop a decision-making model of a dynamic fidelity indicator (DFI) for adaptive variable-fidelity (VF) analysis and to apply it to practical engineering problems, including computational design optimization. The biggest advantage is considerable computation efficiency while satisfying solution accuracy. Bayesian-based DFI and difference-based DFI are formulated as probabilistic model validation metrics to quantify model-form uncertainties attributed to the VF analysis. Two adaptive VF surrogate models of the VF kriging with regression and sample reinterpolation and the simple VF kriging with an additive bridge function are developed. The VF kriging models are integrated with the DFIs into an efficient global optimization design framework for the design problems, which was further improved by the multipoint and multi-objective infill sampling criteria. Validation of the developed framework is carried out with two analytic functions for solution optimality and computational efficiency. As a practical design application, the NLR 7301 multi-element airfoil with a flap is designed for high lift while the model-from uncertainty is defined by different flow solutions of the Euler and Reynolds-averaged Navier–Stokes equations. The results show that the design optimization becomes more efficient with great accuracy by the adaptive VF analysis with the DFIs.

Aerodynamic Analysis of Multi Element Airfoil

The flow over multi-element airfoils has been numerically investigated in ANSYS fluent and has been compare the aerodynamic parameters with the standard NACA airfoils 4412 and 0012. The 2D viscous, transient, pressure model equations together with the k-ω turbulence model were applied to this numerical simulation utilizing the multiblock unstructured grids of sphere of influence type. Numerical results showed that the aerodynamic parameters of multi element airfoils with tail effect are much optimum than the standard NACA airfoils. Also the analysis is made on different flap and slat angles of different conditions and the optimization of multi element airfoils has been performed.

Lift Augmentation Based on Flap Deflection With Dielectric Barrier Discharge Plasma Flow Control Over Multi-Element Airfoils

The effect of the lift augmentation of multi-element airfoils with increased flap deflection and dielectric barrier discharge (DBD) plasma flow control on the flap at several angles of attack (AOAs) is investigated numerically and experimentally. A phenomenological body force model is employed to simulate the DBD actuators at Re = 1.03 × 106. The simulation results show that the atmospheric plasma generated by the DBD actuators completely suppresses the flow separation over the flap at several AOAs, and consequently, the lift augmentation of a multi-element airfoil can be achieved over the entire prestall AOA range. A corresponding flow control experiment on a multi-element airfoil performed in a low-speed wind tunnel at a freestream velocity of 30 m/s is presented; in this experiment, particle image velocimetry (PIV) was employed for flow visualization over the upper surface of the flap. The PIV results demonstrate that the flow separation on the flap is suppressed completely by the same DBD actuators used in the simulation.

Investigation of water impingement on a multi-element high-lift airfoil by Lagrangian and Eulerian approach

McDonnell Douglas Aerospace (MDA) high-lift model is widely used in the study of multi-element airfoil, while there is still short knowledge of ice accretion and water impingement on it. In this paper, based on two-phase flow theory, two numerical models were presented by using both Eulerian approach and Lagrangian approach, respectively, in order to predict the water impingement efficiency on a two-dimensional (2D) multi-element high-lift airfoil. Both computational results were validated with the experiment data, which shown good agreements in the impingement limitations and tendency. The trend that how the attack angle and droplet diameter affect the feather of local water impingement characteristics on the different elements of MDA were further investigated. As shown in this research, the trends that the local impingement intensity and extent on flap of MDA varied differently as in general understanding due to the complex structures of flow field, which should be careful cognized in design of the ice protection system.

A Solution Adaptive Cartesian Grid Based Euler Solution for Compressible Flow Around BOEING TR-1322 Multi-element Airfoil

Cartesian grids constitute a special branch in unstructured grid technology. They use specially designed algorithms to generate automatic grids for complex geometries and to simulate flows around such geometries regardless of the body shape and number of bodies. Cartesian grids are generated by constructing a quadtree based data structure for the purpose of connecting the Cartesian cells to each other. A “hands-off”, Cartesian grid generator based Euler solution called GeULER is implemented in object-oriented FORTRAN programming language. In this study, implementations of generated two-dimensional adaptive refinement/coarsening scheme codesare appended to the developed compressible flow solver by using special Cartesian-based algorithms, namely cut-cell adaptation and curvature adaptation around BOEING TR-1322 multi-element airfoil. A subsonic flow at free stream Mach number of 0.11 around the airfoil is tested to predict pressure distributions around it and Mach contours of the flow are depicted by using the developed GeULER code.

Flow Control Using Air-Jet to Improve the Aerodynamic Performance of a Multi-Element Airfoil

This paper describes the application of active flow control for the NLR7301 supercritical airfoil/flap configuration at Re = 2.51x106. A parametric analysis is conducted to investigate the effects of jet parameters (jet direction, jet location and momentum coefficient) on the aerodynamic performance of a multi-element airfoil. The results indicate that flow separation is delayed and efficiency of jet can be improved with specific momentum coefficient (the best lift-drag ratio at Cμ=0.16) and jet angle (16°) when the jet is located near the separation point of the airfoil.

Parameter Optimization Research on Lift-enhancing of Multi-element Airfoil Using Air-blowing

Based on the response surface methodology and the grid method combining with numerical simulation of Reynolds-averaged Navier-Stokes equations,the lift-enhancing optimizations of three-element airfoil parameters and its air-blowing flow control parameters are carried out. The finite volume method is adopted to discretize the Reynolds-averaged Navier-Stokes equations in space, the second-order upwind scheme is used in time advance, and SST k – ω turbulence model is used to compute turbulence viscosity. The objective function is obtained with the response surface methodology,and the optimal solution is made using nonlinear programming with the grid method. On the base of multi-element airfoil parameter optimization, the influencing parameters ofair-blowing effect are analyzed and selected, the optimization design variables are determinedas the air-blowing slotlocations, angles and air-blowing momentumcoefficients, and lift-enhancing aerodynamic optimization ofair-blowing flow control parameters on multi-element airfoil is completed. It is shown from the results that the optimization method combining response surface methodology with the grid method is fit for parameter optimizationof multi-element airfoil and its flow control with air-blowing on the flap forlift-enhancing; the flow around the multi-element airfoil can be well controlled and its aerodynamic performance is greatly improved, then the maximum lift coefficient achieves 4.9589which is usually the maximum lift coefficient of the five-element airfoil; after optimization the air-blowing slot anglesare of about 20° on the trailing edge flapsand the air-blowing momentum coefficientsof slotsexist an optimum value.

Discontinuous Galerkin and Petrov Galerkin methods for compressible viscous flows

In this paper, high-order finite-element discretizations consisting of discontinuous Galerkin (DG) and streamline upwind/Petrov Galerkin (SUPG) methods are investigated and developed for solutions of two- and three-dimensional compressible viscous flows. Both approaches treat the discretized system fully implicitly to obtain steady state solutions or to drive unsteady problems at each time step. A modified Spalart and Allmaras (SA) turbulence model is implemented and is discretized to an order of accuracy consistent with the main Reynolds Averaged Navier–Stokes (RANS) equations using the present high-order finite-element methods. To accurately represent the real geometry configurations for viscous flows, high-order curved boundary meshes are generated via a Computational Analysis PRogramming Interface (CAPRI), while the interior meshes are deformed subsequently through a linear elasticity solver. The mesh movement procedure effectively avoids the generation of invalid elements that can occur due to the projection of curved physical boundaries and thus allows high-aspect-ratio curved elements in viscous boundary layers. Several numerical examples, including large-eddy simulations of viscous flow over a three-dimensional circular cylinder and turbulent flows over a NACA 4412 airfoil and a high-lift multi-element airfoil at high angles of attack, are considered to show the capability of the present high-order finite-element schemes in capturing typical viscous effects such as flow separation and to compare the accuracy between the high-order DG and SUPG discretization methods.

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.

Flow Simulations by Enhanced Implicit-Hole-Cutting Method on Overset Grids

Based on a hierarchical overset-grid strategy, enhanced implicit-hole-cutting method has been applied to the study of viscous flows around 30P30N multi-element airfoil and the wing–body configuration of the NASA common research model. Numerical simulations were performed on overlapping grids by an in-house computational fluid dynamics solver called Exstream. The present paper conducted the grid-convergence and buffet study of the NASA common research model, which was used in the Fifth AIAA Computational Fluid Dynamics Drag Prediction Workshop. The result of the 30P30N multi-element airfoil proves that the enhanced implicit-hole-cutting method and Exstream solver could obtain great robustness and accurateness. From the result of the grid-convergence study, the value of total drag follows a nearly linear trend and seems to converge to a given value under different grid refinements. Moreover, grid density has a nonnegligible impact on the skin-friction drag component. The consequence of buffet study reveals that there is a very interesting variation of lift coefficient that it decreases from 0.599 to 0.587 when the angle of attack increases from 3.00 to 3.25 deg. The streamlines and surface-pressure contours show that a flow separation bubble appears near the trailing edge of the wing–fuselage junction. Extrafine overlapping grid, matched structured grid, and different turbulence models have been tested for the flow separation bubble.

Study of Burst Wakes in a Multi-Element Airfoil Flowfield

High-lift multi-element airfoils, such as those used on large transport aircraft during takeoff and landing, can generate strong adverse pressure gradients that, while the surface flow is attached, can cause off-the-surface separation in the wake: so-called wake bursting. The sudden expansion and thickening of the separated wakes has been shown to decrease lift and increase drag. Wake bursting was experimentally studied over a three-element high-lift airfoil, and unsteady velocity measurements were taken with a split-film probe. The tests were performed in the University of Illinois at Urbana–Champaign low-speed low-turbulence subsonic wind tunnel on a multi-element airfoil with a chord length of 1.35 ft (0.411 m) and a model span of 2.8 ft (0.85 m). Results for a Reynolds number of indicate that wake bursting was observed for the wake of the main element and the first flap. A methodology was developed to numerically define the core of each wake both upstream and downstream of the burst point. Data show that the local flowfield angle in the wake core does not significantly change relative to the flowfield outside the wake core. Unsteady results indicate that the velocity fluctuations within the burst-wake region are dominated by turbulence in the shear layers between the wakes with less turbulence observed in the wake cores. These turbulent fluctuations were largest in the shear layers and were observed to spread into the wake cores.

High-Lift Effect of Bionic Slat Based on Owl Wing

A slat without a cove is built on the basis of a bionic airfoil (i.e. stowed multi-element airfoil), which is extracted from a long-eared owl wing. The three-dimensional models with a deployed slat and a stowed slat are measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect: compared with the stowed slat, the deployed slat works more like a spoiler at low angles of attack, but like a conventional slat or slot at high angles of attack. In addition, it can also increase stall angle and maximum lift coefficient, and postpone the decrease in the gradient of the lift coefficient. At the same time, the flow field visualized around both three-dimensional models suggests the leading-edge separation associated with the decrease in the gradient of the lift coefficient. Furthermore, the related two-dimensional simulation well agrees with the analysis of the lift coefficient, as the complement to the experiment. The bionic slat may be used as reference in the design of leading-edge slats without a cove.

High-Lift Mechanism of a Bionic Slat

To avoid broadband noise from a slat cove, the deployed slat contour is usually modified by filling cove, but the design is sensitive to aerodynamic performance. In the paper, a bionic slat without a cove is built on the basis of a bionic airfoil (i.e. stowed bionic multi-element airfoil), which is extracted from a long-eared owl wing. The quasi-two-dimensional models with a deployed bionic slat and a stowed bionic slat are manufactured by rapid manufacturing and prototyping system, respectively, and measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect: the lift coefficients of the model with a stowed slat are larger at less than 4°angle of attack, but the model with a deployed slat has the larger lift coefficients at greater than 4°angle of attack. Furthermore, the deployed bionic slat can increase stall angle and maximum lift coefficient, but also delay the decline of the lift coefficient curve slope meaning that the leading-edge separation is postponed within a certain range of angle of attack. At the same time, the flow field around the models is visualized by smoke wire method. The leading-edge separation of the model with a stowed slat is shown at low Reynolds number and angle of attack. However, the finding does not occur in the flow field of the model with a deployed slat at the same conditions, probably because the gap between the bionic slat and the main wing results in favorable pressure gradient, the deployed bionic slat decreases the peak of adverse pressure gradient by increasing the chord of the bionic multi-element model, and the bionic slat wake excites transition to the boundary layer on upper surface of the main wing. This superiority may be used as reference in the design of the leading-edge slat without a cove.

Wind Tunnel Test of Effect of Sound-Absorbing Material on Lift of Two-Element Airfoil

The flow parameters of fluctuating pressure and fluctuating velocity in the gap can be changed by the porous absorption material on the leading edge of upper surface of the flap of multi-element airfoil (GAW-1),and the aerodynamic characteristics is also altered. Experiment was conducted in the NF-3 wind tunnel. It turns out that porous absorption material has a significant effect on fluctuating velocity (i.e. turbulent kinetic energy), and the lift coefficient drops when fluctuating velocity increases ; but the influence on RMS of fluctuating pressure on upper surface is not obvious; the average speed in gap is reduced. The PSD of fluctuating pressure and fluctuating velocity show that low-frequency signal has a more obvious influence on lift of multi-element airfoils than high-frequency.

Numerical Study of the Aerodynamic Characteristics of a Multi-Element Airfoil NACA 23012

Numerical Study of the Aerodynamic Characteristics of a Multi-Element Airfoil NACA 23012

The physics of modeling unsteady flaps with gaps

Research indicates that active control concepts have promise in mitigating numerous adverse phenomena associated with the aeromechanics of lifting surfaces. These techniques are being applied to delay stall of fixed wing aircraft, as well as to eliminate or mitigate vibratory loads, blade–vortex interaction, and dynamic stall of the flow about rotorcraft and wind turbine blades. These phenomena are nonlinear and unsteady for dynamic systems, which add yet another layer of complexity on the physics of the flow. While a plethora of different active control techniques is being explored, the use of trailing edge flaps appears to be one of the more viable and cost-effective concepts. Static multi-element airfoils and wings have been analyzed computationally, but little exists on the ability to model these when the airfoil and flap are dynamic. The costs associated with modeling the gap between the airfoil and flap have led to approximations where the flap is modeled only as a morphed tip of the airfoil (no gap). Using a hybrid Reynolds-Averaged Navier–Stokes/Large-Eddy-Simulation turbulence technique, an oscillating flapped airfoil has been studied to determine the influence of modeling the gap on the performance and acoustic signature of the airfoil. Results are compared with the experimental data to confirm the validity of the computational approach. Both attached and separated (dynamic stall) oscillating flows are examined. The physics within the gap are found to be important for the airfoil performance when stall is encountered, as well as when acoustic signatures are required.

The Design of Multi-Element Airfoils Through Multi-Objective Optimization Techniques

This paper presents the development and the application of a multi-objective optimization framework for the design of two-dimensional multi-element high-lift airfoils. An innovative and efficient optimization algorithm, namely Multi-Objective Tabu Search (MOTS), has been selected as core of the framework. The flow-field around the multi-element configuration is simulated using the commercial computational fluid dynamics (cfd) suite Ansys cfx. Elements shape and deployment settings have been considered as design variables in the optimization of the Garteur A310 airfoil, as presented here. A validation and verification process of the cfd simulation for the Garteur airfoil is performed using available wind tunnel data. Two design examples are presented in this study: a single-point optimization aiming at concurrently increasing the lift and drag performance of the test case at a fixed angle of attack and a multi-point optimization. The latter aims at introducing operational robustness and off-design performance into the design process. Finally, the performance of the MOTS algorithm is assessed by comparison with the leading NSGA-II (Non-dominated Sorting Genetic Algorithm) optimization strategy. An equivalent framework developed by the authors within the industrial sponsor environment is used for the comparison. To eliminate cfd solver dependencies three optimum solutions from the Pareto optimal set have been cross-validated. As a result of this study MOTS has been demonstrated to be an efficient and effective algorithm for aerodynamic optimizations. Copyright © 2012 Tech Science Press.

An automatic unstructured grid generation method for viscous flow simulations

High aspect-ratio grids are required for accurate solution of boundary layer and wake flow. An approach for the efficient generation of isotropic and stretched viscous unstructured grids is introduced in this paper. The proposed grid generation algorithm starts with a very coarse initial grid. In far field regions, isotropic cells of excellent quality are produced using a combination of point insertion and cell subdivision techniques. Simultaneously, a directional grid refinement strategy is used to construct highly stretched triangular cells in viscous dominated regions. First, anisotropic unstructured grids are produced in the stream-wise direction. Then, cells close to the solid surface are refined to highly stretched layer of triangles suitable for boundary layer region. The accuracy of the current grid generation approach is assessed by laminar and turbulent compressible flow solutions around NACA0012, RAE2822, and NHLP multi-element airfoils. Numerical flow simulation results are compared with published data. Comparisons point to accuracy of the proposed unstructured viscous grid generation procedure.

Transition prediction of high-lift wing

Transition simulation of plane, named as T3A/T3B, and NLR7301 multi-element airfoil were presented in this article as verification case for the γ-Re θ t transition model proposed by Menter & Langtry. Furthermore, the transition past high-lift wing with leading edge and trailing edge flaps was investigated using fully turbulence model and transition model. Results indicated that transition had an important affect on the aerodynamic characteristics of high-lift wing. The simulation could provide suggestion for disign of high-lift wing, especially the selection of the gap between main wing and flap and the deflection angle of second flap.