S809 Airfoil Research Articles

Calibration of the Critical Amplification Factor for Reynolds-Averaged Navier–Stokes-Based Transition Modeling

The present study uses an adjoint-based gradient optimization framework to perform calibration of the critical amplification factor for transition models based on the linear stability theory. More specifically, the two-equation amplification factor transport model is used, and the critical amplification factor, which directly controls the onset of the transition via the source term of the intermittency equation, is calibrated for a set of canonical flat plate test cases in both bypass and natural transitional regimes. It is shown that, by utilizing a sigmoid fitting of the turbulence index profile, the transition onset location can be accurately predicted in a differentiable and smooth fashion, which is essential to the adjoint-based sensitivity analysis of the Reynolds-averaged Navier–Stokes solver. Subsequently, the results of these calibration studies are used for obtaining a new relation via a high-order polynomial regression model relating the critical amplification factor to the freestream turbulence intensity. Finally, the prediction capability of the calibrated relation is tested for natural transitional flows past NLF(1)-0416 and S809 airfoils. The numerical results show significant improvements in predicting the transition onset location as well as lift and drag predictions.

Aerodynamics of a three-dimensional bionic morphing flap

Avian wings are characterized by intricate feather movements to manipulate airflow and enhance aerodynamic performance. The wing trailing-edge undergoes continuous gradual transformations to enact camber reflexes. A three-dimensional bionic flap inspired by the avian wings is proposed. The flap undergoes spanwise morphing to generate seamless wave-like deformations at the trailing-edge. The performance of S809 airfoil fitted with various spanwise morphing flaps, and conventional flaps, is studied. Comprehensive investigations are performed to analyze the aerodynamic forces, pressure-fields, and velocity evolution across the airfoils fitted with different flaps, subjected to various deflection angles and angles of attack, at the Reynolds number of 106. The analyses exhibit significance of variable mean airfoil-camber on the aerodynamic performance. Comparative analyses demonstrate the superiority of morphing flaps over the conventional ones with regards to- lift increment, drag reduction, and enhanced glide ratio. Further, flow-field visualization and surface-flow measurements reveal unique 3D-evolution of the inflow in streamwise and spanwise directions. The spanwise morphing significantly delays flow separation and aids turbulence suppression. The downstream wake-velocity profiles are also found to be considerably reformed by the spanwise morphed flap topology. Overall, the study establishes supremacy of spanwise morphing over the conventional design in terms of achieving optimal aerodynamic performance.

Multifidelity Analysis of a Solo Propeller: Entropy Rise Using Vorticity Dynamics and Kinetic Energy Dissipation

Propellers for electric aviation are used in solo- and multirotor applications. Multifidelity analysis with reduced cycle time is crucial to explore several designs for energy minimization and range maximization. A low-fidelity design tool, py_BEM, is developed for design and analysis of a reverse-engineered solo 2-bladed propeller using blade-element momentum theory with physics enhancements including local Reynolds number effect, boundary-layer rotation, airfoil polar at large AoAs and stall delay. Spanwise properties from py_BEM are converted into 3D blade geometry using T-Blade3. S809 and NACA airfoil polar are utilized, obtained by XFOIL. Lift, drag, performance losses, wake analysis, comparison of 3D steady CFD with low fidelity tool, kinetic energy dissipation, entropy and exergy through irreversibility are analyzed. Spanwise thrust and torque comparison between low and high fidelity reveals the effect of blade rotation on the polar. Vorticity dynamics and boundary-vorticity flux methods describe the onset of flow separation and entropy rise. Various components of drag and loss are accounted. The entropy rise in the boundary layer and downstream propagation and mixing out with freestream are demonstrated qualitatively. Irreversibility is accounted downstream of the rotor using the second-law approach to understand the quality of available energy. The performance metrics are within 5% error for both fidelities.

Accelerate the convergence of turbulent flows simulation: A novel progressive locally power-law preconditioning method

In this study, an extended progressive preconditioning technique called the locally power-law preconditioning method (LPLPM) is employed for analyzing unsteady and steady turbulent flows for the first time. This technique's effectiveness and convergence rate are compared to the standard and Malan's preconditioning methods, along with the artificial compressibility approach. In all methods, a finite volume and the four-stage local time Runge-Kutta schema are applied to discretize the space and the time derivative terms of governing equations, respectively. In the LPLPM, the preconditioning matrix is automatically adapted using flow-field velocity sensors via a power-law relation. The turbulence model coupled with the governing equations is the BSL-k−ω model. To investigate the efficiency and accuracy of the LPLPM, different test cases are performed for flows over S809, NACA0012, and ONERA airfoils at various Reynolds numbers (1.0 × 106 to 5.25 × 106) and angles of attack (0 to 16 (deg)). A sensitivity evaluation is performed to investigate the impacts of numerical variables on the solution. The results reveal that the LPLPM is accurate, robust, and computationally efficient in simulating turbulent flows and significantly improves the convergence rate up to 71% and 43% reductions in the iteration number for simulating steady and unsteady turbulent flows, respectively.

A new data assimilation method of recovering turbulent mean flow field at high Reynolds numbers

This paper proposes a new data assimilation method for recovering the high-fidelity turbulent mean flow field around airfoil at high Reynolds numbers based on experimental data, which is called Proper Orthogonal Decomposition Inversion (POD-Inversion) data assimilation method. Aiming at flows including shock wave discontinuities or separation at high angles of attack, the proposed method can reconstruct the high-fidelity mean flow field combined with experimental force coefficients. We firstly perform the POD analysis to turbulent eddy viscosity fields computed by the SA model and obtain base POD modes. Then the POD coefficients are optimized by global optimization algorithm coupling with computational fluid dynamics (CFD) solver. The high-fidelity turbulent mean flow fields are recovered by several main modes, which can dramatically reduce dimensions of the system. The effectiveness of the method is verified by cases of transonic flow around the RAE2822 airfoil at high Reynolds numbers and the separated flow around S809 airfoil at high angles of attack. The results demonstrate that the proposed data assimilation method can recover turbulent flow fields which optimally match the experimental data, and can significantly reduce the error of aerodynamic coefficients. Furthermore, the proposed method can provide high-fidelity mean field data to establish turbulence models based on machine learning.

Calibration of the Transitional Turbulence Model

In the present paper, the turbulent transition model from Langtry and Menter (“Correlation-Based Transition Modeling for Unstructured Parallelized Computational Fluid Dynamics Codes,” AIAA Journal, Vol. 47, No. 12, 2009, pp. 2894–2906) is implemented in the structured finite volume Reynolds-averaged Navier–Stokes code FANSC and coupled with the shear-stress transport turbulence model. The model is modified and recalibrated to better match experimental results. The local turbulent intensity is replaced with a more consistent turbulent fluctuation representation to avoid nonphysical solutions at the stagnation point that would contaminate the downstream boundary-layer predictions. A calibration is devised by customizing several constants involved in the equation for the intermittency and the destruction term for the turbulent kinetic energy . An optimization algorithm is thus employed to facilitate the calibration on well-known two-dimensional test cases, such as the flat plates of the T3 series and of Schubauer and Klebanoff (“Contributions on the Mechanics of Boundary-Layer Transition,” NACA TN 3489, 1955), as well as the NACA 0012 airfoil. The calibrated model is then validated on the NLF-0416 and S809 airfoil cases that have not been involved in the optimization process.

Insight into the effects of leading edge delamination on the aerodynamic performance of an airfoil and wind turbine

Severe erosion or delamination at the leading edge of blades has an adverse influence on the power loss of wind turbines. Obtaining relevant quantitative data and its mechanisms would help in the efficient management and maintenance of these turbines. In the present work, detailed analysis on the effects of various levels of leading edge delamination on the aerodynamics and flow characteristics of an S809 airfoil and, in turn, on the performance of the NREL phase VI rotor is conducted. The results indicated that an elongated leading edge separation bubble and two enclosed vortex systems appeared in the delaminated region of the airfoil when the delamination levels aggravate to a certain degree, while the trailing edge separation vortex can be observed for all delaminated airfoils. The aerodynamic performance of the wind turbine decreases with increasing delamination depth and increases with growing delamination depth. The most influential delamination length is 1%c, and the maximum power loss is 23.09% for the blade with the severe delamination case. A small area of deep leading edge delamination or defects may cause great power loss, which should not be ignored in practice engineering.

Research on dynamic aerodynamic performance of wind turbine airfoil under large blade deformation

With the increase of wind power blades, the amount of blade design pre-bending and deformation in motion has increased significantly. Under the condition of large deformation of the wind turbine blade, the pitch axis deviates greatly from the centerline of the airfoil. At this point, the pitch movement of the wind turbine blade will lead to the dynamic change of the airfoil angle of attack and the horizontal movement of the airfoil at the same time. Concerning this problem, the dynamic stall characteristic of the S809 airfoil under the condition of large deformation was studied using CFD technology. The results show that the horizontal motion caused by the deviation of the pitch axis from the airfoil center can significantly change the stall characteristic of the airfoil. Based on this, the fatigue load changes caused by changes in dynamic stall characteristics under typical operating conditions are studied.

Aerodynamic characteristic of wind turbine with the leading edge slat and Microtab

The leading edge slat can increase the flow energy of airfoil suction surface, and Microtab can hinder the flow of pressure surface. In order to combine the advantages of two passive flow control methods, this paper creatively proposed to combine the leading edge slat with Microtab to simulate the S809 airfoil, which slat had the contour characteristics of S809 airfoil. The transition SST turbulence model was applied to estimate the aerodynamic characteristics of the S809 airfoil. According to research, the flow control approach of the leading edge slat combined with Microtab could effectively restrain the flow separation and ameliorate the aerodynamic characteristics of the S809 airfoil. For Case-12, when the airfoil angle of attack was 16.22°, the boundary layer flow separation was restrained completely, Cl was increased to 3.06 from 1.79 and increased by 171% compared with clear airfoil. Research shown that the position of slat, the position and height of the Microtab were significant factors for the aerodynamic characteristics of the S809 airfoil. Microtab position at 0.95c and height at 0.03c performed the best effect to inhibit flow separation and improve lift coefficients.

Numerical study on the influence of vortex generators on wind turbine aerodynamic performance considering rotational effect

Based on the γ-Reθt transition model, the S809 airfoil and Phase VI wind turbine rotating blades are simulated and compared with the experimental data. In order to explore the three-dimensional rotation effect (TDRE) on aerodynamic performance, the aerodynamic characteristics and flow fields structure of the blade and airfoil under the same Re are compared. The Inverse blade element moment (IBEM) method is used to obtain the local angle of attack (AoA) and relative velocity of the wind turbine blade. In addition, the flow fields of each blade section with and without vortex generators (VGs) are compared, and the influence of VGs on the flow separation is analyzed through the output torque and pressure coefficient of the wind turbine. The results show that the TDRE is obvious at the blade root, which can effectively delay the separation; VGs further delay airflow separation on the blade surface and increase the lift coefficients (CL) of 0.3R blade section at 10 m/s and 13 m/s by 4.4% and 0.6%. The output torques of the wind turbine with VGs are raised by 3.73%, 8.74% and 10.82% at 10, 13 and 15 m/s respectively. The calculated results are in good agreement with the results of Phase VI wind turbine and the Ohio State University (OSU) test.

CFD Comparative Study on Bended and 2D Airfoils on HAWT Performance

The design of a conventional horizontal axis wind turbine (HAWT) is based on the aerodynamic characteristics of a two-dimensional (2D) airfoil. The rotational motion and the consequent aerodynamic effects, of HAWT’s rotor, do not guarantee an optimal design point that matches the 2D airfoil characteristics. The present work studies the diversion of the flow due to the spanwise velocity component in a rotating reference frame. It suggests that a slight deviation in the flow away from the chordwise direction could alternate the characteristics of the airfoil profile. A bended profile with a circular arc was extracted from a baseline rotating blade, flattened, and modelled against the 2D S826 airfoil. The results show a substantial discrepancy in the airfoil characteristics which could influence the turbine efficiency. Therefore, it suggests using a pre-bended airfoil (3D) while modeling the blade, so the circular section will match the correct airfoil coordinates. The proposed bended-profile version was modeled against the baseline blade. This novel blade shows an augmentation in the power coefficient up to 5.4% starting from the design point to high tip speed ratios (TSR) and low wind speeds.

Comparative Study of Dynamic Stall between an Aircraft Airfoil and a Wind Turbine Airfoil in an Air–Particle Flow

Dynamic stall in clean air flow has been well studied, but its exploration in air–particle (air–raindrop or air–sand) flow is still lacking. The aerodynamic performance loss of aircraft (NACA0012) and wind turbine (S809) airfoils and their differences during the hysteresis loop at different pitching parameters are also poorly understood. As shown in this paper, the reduced frequency has little effect on the value of the maximum lift coefficient increment caused by particles, but a larger one can enhance the hysteresis effect and drag the angle of attack, at which the maximum increment is obtained, from the up stroke to the down stroke. The large lift coefficient increments of two airfoils and their difference also have a similar change trend with the reduced frequency. Compared to that of NACA0012 airfoil, the increments of S809 airfoil are obviously greater at three mean angles of attack, especially at 8°, which is the commonly used operating angle. In addition, the angle of attack, at which the maximum lift coefficient is obtained, can be significantly changed by particles in two regions: one is under the effect of deep stall, the other is under the effect of light stall at a low, reduced frequency.

Combined effect of passive vortex generators and leading-edge roughness on dynamic stall of the wind turbine airfoil

Dynamic stall causes the highly unsteady and nonlinear aerodynamic loads on wind turbines. Recently, dynamic stall with passive vortex generators (VGs) and leading-edge roughness (LER) has received considerable attention, but independently. Therefore, this paper presents a careful investigation into dynamic stall of the NREL S809 airfoil with both VGs and LER to reveal their combined effect. Fully-resolved URANS simulations are conducted to identify the unsteady flow characteristics, and equivalent sand-grain roughness is used to model LER. LER significantly increases the turbulence kinetic energy (TKE) and suction loss at the leading edge, thereby causing the earlier onsets of separated flow and dynamic stall. Increasing roughness height generally reduces linear lift-curve slope, increases aerodynamic hysteresis and makes the separated flow hard to be reattached. VGs increase near-wall TKE via streamwise vortices and effectively suppress the separated flow. Dynamic stall is therefore significantly delayed by VGs with higher maximum lift, and aerodynamic hysteresis is also greatly reduced with the flow reattachment accelerated. Interestingly, serious LER may cause strong vortical disturbances and change the dynamic stall behaviors from light stall into deep stall. Double-row VGs are also found better than single-row VGs in improving the aerodynamic performance of roughened airfoil. These findings imply that VGs effectively control dynamic stall and diminish the adverse LER effect. This study should advance the control of unsteady loads on wind turbines suffering from harsh environmental conditions.

Influence of the Curvature Correction on Turbulence Models for the Prediction of the Aerodynamic Coefficients of the S809 Airfoil

Using the appropriate procedure, Computational Fluid Dynamics allows predicting many things in several fields, and especially in the field of renewable energies, which has become a promising research axis. The present study aims at highlighting the influence of the curvature correction on turbulence models for the prediction of the aerodynamic coefficients of the S809 airfoil using the Computational Fluid Dynamics code ANSYS Fluent 17.2. Three turbulence models are used: Spalart-Allmaras, Shear Stress Transport k-ω and Transition SST. Experimental results of the 1.8 m × 1.25 m low-turbulence wind tunnel at the Delft University of Technology are used in this work for comparison with the numerical results for a Reynolds number of 106. The results show that the use of the curvature correction improves the prediction of the aerodynamic coefficients for all the turbulence models used. A comparison of the three models is also made using curvature correction since it gave better results. The Transition SST model is the one that gives the best results for the lift coefficient, followed by the Shear Stress Transport kω model, and finally the Spalart-Allmaras model. For the drag coefficient, Transition SST model is the best, followed by the Spalart-Allmaras model, and finally the Shear Stress Transport kω model.

Numerical Investigation of Performance Enhancement of the S809 Airfoil and Phase VI Wind Turbine Blade Using Co-Flow Jet Technology

Making full use of wind energy can effectively alleviate the global energy shortage and environment contamination problems. Nevertheless, how to significantly improve the performance of the wind turbine airfoil and blade is a crucial issue. As the novel flow control method, the co-flow jet (CFJ) technology is one of the most potential methods to solve this problem. Thus, the effects of the CFJ technology on the performance enhancement of the S809 airfoil and Phase VI wind turbine blade are explored in this study. Furthermore, the effects of the injection location and jet momentum coefficient are studied, and an adaptive jet momentum coefficient strategy of the CFJ technology is proposed. Results demonstrate that the CFJ technology can significantly improve the maximum lift coefficient and maximum corrected lift-to-drag ratio of the S809 airfoil. Moreover, the power coefficient of the Phase VI wind turbine blade at the low tip speed ratio is greatly enhanced as well. In particular, the maximum lift coefficient and maximum corrected lift-to-drag ratio of the typical S809 CFJ airfoil with adaptive Cμ are improved by 119.7% and 36.2%, respectively. The maximum power coefficient of CFJ blade can be increased by 4.5%, and the power coefficient of CFJ blade can be boosted by 226.7% when the tip speed ratio is 1.52.

Effects of leading edge slat on the aerodynamic performance of low Reynolds number horizontal axis wind turbine

The present study considers the use of a slat near the leading edge of an airfoil to delay or completely cancel separation and thus improves the performance of small wind turbines, in addition to lowering the cost of the blade by reducing the used material. Flow around the S809 airfoil with a slat is numerically simulated using ANSYS 2019 R1 (CFD) program. The present work concentrates on two geometrical parameters namely the location of the slat relative to the base airfoil and the chord size of the slat. Relative to the total chord length of the main airfoil, a slat with a chord length 10% is located at range of distances +3.6% to +10.8% in y direction, slat located at 9% shows the best lift coefficient. To study the effect of slat size, slat sizes range from 5% to 12.5% are numerically investigated, slat size 7.5% shows the best lift coefficient and attached flow over the airfoil for a wide range of angles of attack. The improvement is achieved with the same total chord length with 12% saving of material which corresponds to 6% of the total cost of the turbine.

A study for the effect of slat installation on aerodynamic performance of S809 airfoil

A study for the effect of slat installation on aerodynamic performance of S809 airfoil

IDDES simulation of the performance and wake dynamics of the wind turbines under different turbulent inflow conditions

This paper aims at investigating the effect of the inflow turbulence on the aerodynamics and the wake instabilities of the wind turbine. The improved delayed detached eddy simulation (IDDES) combined with the overset grid method is performed to model the NREL S826 airfoil wind turbine at design operating condition (λ=6.0). The mean loads of power coefficient (CP) and thrust coefficient (CT) show good agreement with existing experiments data. The normalized mean velocity U/Uref profile and normalized turbulent kinetic energy k/U2ref profile within the wake is also consistent with the experiments data, indicating a fairly accurate predictions of the wake turbulence. The detailed analysis of wake vortex structure, mean Reynold's stress distribution and PSD spectrum of turbulent kinetic energy are utilized to explore the effect of incoming turbulence on the wind turbine performance and the mechanism of the wake instability. The incoming turbulence and wind shear may promote the tip vortex instability and accelerate wake recovery, thus more attention should be paid to the design procedure and layout of wind farms.

A combined method of CFD simulation and modified Beddoes-Leishman model to predict the dynamic stall characterizations of S809 airfoil

The Beddoes-Leishman model (B-L model) was widely applied in the airfoil's dynamic loads prediction. But the need for numerous experimental parameters greatly limits its application range. In this study, numerical simulation was used to simulate the wind tunnel experiments of airfoils to obtain the required parameters. Take the S809 and NACA0012 airfoils as examples, Fluent software was used to calculate the static parameters, and dynamic mesh technology was used to simulate the sinusoidal oscillation wind tunnel experiments of airfoils to obtain the dynamic parameters. Use the modified B-L model with the obtained parameters to predict the dynamic stall characteristics of the airfoils. The predicted results are in good agreement with the experimental data of the wind tunnel, which means that it is promising to use numerical simulation to calculate the parameters required by the B-L model to predict the dynamic stall characteristics of an airfoil. It provides a simpler and more feasible method for predicting the dynamic loads of the blade of wind turbines and tidal current turbines.

Performance analysis of three heuristic algorithms for airfoil design optimization

ABSTRACT The airfoil design optimizations are often limited due to the high computational cost and complex algorithm selections. However, such computational requirement has not been fulfilled well because some major unpaired performances exist between the mathematical benchmarks and airfoil designs. In this study, we compared three heuristic optimization algorithms: hill-climbing algorithm (HC), simulated annealing algorithm (SA), and genetic algorithm (GA), using three test functions in the airfoil design optimization of the wind turbines. The results show that with functions representing relatively flat shape, the HC and the SA are faster to find the global optimum than the GA. Tested with multimodal functions such as Shubert function, however, it is found that the HC and SA failed to find the global optimum although the SA has better possibilities to jump out the local extremum than the HC. For the airfoil optimization of S809 and NACA64418, it is found that the SA is more efficient than the GA. After the optimization, the S809 airfoil noise is decreased more than 0.9 dB, and the lift-drag ratio is improved 6.96% compared to its baseline in the given working condition. Similarly, the performance of NACA64418 is also improved with the proposed optimization algorithms. However, when the computational cost is taken into account, the performance of the three widely used algorithms is different from that in the benchmark tests. Therefore, our findings provide important insights of the airfoil design optimization of wind turbines on how to select algorithms and trade-off between computational cost and efficiency.