E387 Airfoil Research Articles

Laminar Separation Control for Eppler 387 Airfoil Based on Resolvent Analysis

By actively controlling laminar separation, the aerodynamic loading can be increased. In the context of turbomachinery, an increased loading allows for more power to be extracted or for a lower part count. Active flow control can be made more effective and efficient if the actuator location and forcing frequency are chosen well. Large-eddy simulations of the flow over an E387 airfoil were carried out for a chord Reynolds number of 100,000. For an angle of attack of zero degrees, the suction-side boundary layer separates laminar to form a large separation bubble. With 1% freestream turbulence intensity, the boundary layer reattaches earlier, and the length of the separated region is in better agreement with available measurements. A resolvent analysis suggests that forcing immediately upstream of separation with an angular frequency of 50 (based on freestream velocity and chord length) provides the maximum forcing-response gain. Guided by the resolvent analysis, active flow control by wall-normal blowing and suction was then investigated in the simulation. Forcing introduces laminar, two-dimensional “rollers” that effectively suppress separation. Without freestream turbulence, transition occurs close to the trailing edge. With freestream turbulence, the flow transitions further upstream and active flow control is less effective.

Geometry Representation Effectiveness in Improving Airfoil Aerodynamic Coefficient Prediction with Convolutional Neural Network

Many applications use symmetric or asymmetric airfoils, such as aircraft design, wind turbines, and heat transfer. Each airfoil has different aerodynamic coefficients. Obtaining the aerodynamic coefficients is a must to optimize the airfoil design. Engineers use various methods to get the airfoil aerodynamic coefficients. A prediction method is an approximation approach that effectively reduces time and cost. This article uses convolutional neural networks (CNN) to get approximation values of those coefficients. In CNN, we collect 8920 aerodynamic coefficients for 223 NACA 4 as labels in datasets by using XFOIL at  and  with varying angles of attacks starting  to  with increment of . The simulation results are compared to the experiment using E387 airfoil for validation. Then, airfoil geometries as part of input datasets were transformed into Grayscale and RGB images using the signed distance function (SDF) and mesh algorithm. Each airfoil representation was trained using an 80% dataset and tested using a 20% dataset with Adam as an optimizer to generate each prediction model using modified LeNet-5. We use three different layer depths in modified LeNet-5 to obtain the optimal layer number. There is no remarkable improvement when varying the depth layers, so four layers are used instead. Simulation results show that using an SDF with Fast Marching Method on CNN predicts the most effective for the airfoil’s lift, drag, and pitch moment coefficient with varying angles of attack simultaneously. One can extend the method by using SDF to recognize different flow conditions.

Numerical Analysis of Wind Turbine Performance Using Different Blade Materials under Wind Load Deflection

A numerical investigation of the deflection on blades of three different materials against the range of wind speeds, and the effect on the blades’ aerodynamic performance was carried out. ABS plastic, wood and glass fiber were used to make blade solid models with Eppler E387 airfoil. Using ANSYS software, wind load impact simulation was carried on the blades over range of operation wind speeds to determine blade tip deflections. Highest and lowest deflection over the range of wind speeds were found to be for ABS plastic blade and glass fibre blade respectively Deflected blades were adopted to a commercial 20 kW wind turbine as a case study. The turbines were subjected to air flow simulation to determine aerodynamic performances over the range of 5m/s to 20m/s wind speeds. At rated wind speed of 10m/s, power coefficient values of 0.52175, 0.53685 and 0.53710 at optimum tip speed ratio (TSR) of 5 were produced by ABS, wood and glass fibre blades respectively. At severe wind speed of 20m/s, corresponding power coefficient values were 0.29911, 0.47458 and 0.58666 respectively. The study indicates that at normal operating winds speeds, all the materials are suitable for blade adoption, while glass fibre material seems to withstand severe wind speed most in aerodynamic performance.

Covert-inspired flaps for lift enhancement and stall mitigation

Even though unmanned aerial vehicles (UAVs) are taking on more expansive roles in military and commercial applications, their adaptability and agility are still inferior to that of their biological counterparts like birds, especially at low and moderate Reynolds numbers. A system of aeroelastic devices used by birds, known as the covert feathers, has been considered as a natural flow-control device for mitigating flow separation, enhancing lift, and delaying stall. This study presents the effects of a covert-inspired flap on two airfoils with different stall characteristics at Reynolds numbers in the order of 105, where small scale UAVs operate. Detailed experiments and simulations are used to investigate how the covert-inspired flap affects lift and drag on an airfoil that exhibits sharp or sudden stall (i.e. the NACA 2414 airfoil) and one that exhibits soft or gradual stall (i.e. an E387(A) airfoil). The effects of the flap chord-wise locations and deflection angles on lift and drag is investigated, through wind tunnel experiments, for two types of flaps namely, a freely-moving flap and a static flap. Results show that the static covert-inspired flap can delay stall by up to 5° and improve post-stall lift by up to 23%. However, the post-stall lift improvement characteristics and sensitivities are highly affected by the airfoil choice. For the soft stall airfoil (i.e. E387(A)), the stall onset delay is insensitive to changing the flap deflection angle, and the flap becomes ineffective when the flap location is changed. In contrast, for the sharp stall airfoil (i.e. NACA 2414), the post-stall lift improvements can be tuned using the flap deflection angle, and the flap remains effective over a wide range of chord-wise locations. Numerical studies reveal that the lift improvements are attributed to a step in the pressure distribution over the airfoil, which allows for lower pressures on the suction side upstream of the flap. The distinctions between the flap-induced lift enhancements on the soft and sharp stall airfoils suggest that the flap can be used as a tunable flow control device for the sharp stall airfoil, while for the soft stall airfoil, it can solely be used as a stall mitigation device that is either on or off.

Passive flow control strategies for low Reynolds number airfoils

This study focuses on ameliorating the aerodynamic performance of an airfoil in low Reynolds number regime by implementing a passive flow control technique to suppress the effects created by the bubble bursting which holds significance in enhancing the aerodynamic performance of SUAVs which fall under this regime. A numerical study is conducted for the flow over E387 airfoil at a Reynolds number 105 to investigate the effects of the implementation of the passive flow control configuration on the laminar separation bubble dynamics. It is noted that orientation, thickness, inlet location, and configuration of the passive flow control passage had imposed significant effects on lift and drag coefficients generated by the airfoil. A significant drag reduction was achieved when the airfoil is implemented with a slot oriented at 30° that has a converging exit which resulted in the rise of the airfoil’s aerodynamic efficiency.

Effect of mach number on high-subsonic and low-Reynolds-number flows around airfoils

High-subsonic and low-Reynolds-number flow is a special aerodynamic problem associated with near space propellers and Mars aircrafts. The flow around airfoils and the corresponding aerodynamic performance are different from the incompressible flow at low-Reynolds-number, due to complex shock wave-laminar separation bubble interaction. The objective of this paper is to figure out the effect of Mach number on aerodynamic performance and special flow structure of airfoil. An in-house Reynolds-averaged Navier–Stokes solver coupled with [Formula: see text] transition model is employed to simulate the flows around the E387 airfoil. The results show that the lift slope is larger than [Formula: see text] in the linear region. No stall occurs even at an attack angle of [Formula: see text]. With increase of Mach number, lift coefficient decreases when attack angle is below [Formula: see text]. However, once the angle of attack exceeds [Formula: see text], higher Mach number corresponds to higher lift coefficient. In addition, the strength and number of shock waves are very sensitive to Mach number. With increase of Mach number, the region of reverse flow vortex near transition location becomes smaller and finally disappears, while a new reverse flow vortex appears near the trailing edge and becomes larger.

Simulation of dielectric barrier discharge actuator at low Reynolds number

PurposeThe purpose of this study is to the modeling of the dielectric barrier discharge (DBD) actuator on the Eppler 387 (E387) airfoil in low Reynolds number conditions.Design/methodology/approachA validated direct-forcing immersed boundary method is used to solve the governing equations. A linear electric field model is used to simulate the DBD actuator. A ray-casting technique is used to define the geometry.FindingsThe purposed model is validated against the former studies. Next, the drag and lift coefficients in the static stall of the E387 airfoil are investigated. Results show that when the DBD actuator is on, both of the coefficients are increased. The effects of the location, applied voltage and applied frequency are also studied and find that the leading-edge actuator with higher voltage and frequency has better improvement in the forces. Finally, the dynamic stall of the E387 with the DBD actuator is considered. The simulation shows that generally when the DBD is on, the lift coefficient in the pitch-up section has lower values and in the pitch-down has higher values than the DBD off mode.Practical implicationsIt is demonstrated that using the DBD actuator on E387 in the low Reynolds number condition can increase the lift and drag forces. Therefore, the application of the airfoil must be considered.Originality/valueThe results show that sometimes the DBD actuator has different effects on E387 airfoil in low Reynolds number mode than the general understanding of this tool.

Effect of active oscillation of local surface on the performance of low Reynolds number airfoil

In low Reynolds number conditions, laminar boundary layer separation and the consequent stall are usual, which are harmful to the aerodynamic characteristics of an airfoil. Energy addition to the flow by active oscillation of local surface can effectively restrain the flow separation and improve the performance. In the present paper, flow control based on active oscillation of local surface on an E387 airfoil is studied with numerical methods. The Reynolds number is Re = 30000 and the location of the oscillation region is a part of the upper surface near the leading edge. The respective relationships between the flow control effect and excitation parameters such as oscillation amplitude and excitation frequency are obtained. The flow mechanisms such as the behavior of the separation vortex and the variation of the equivalent shape are analyzed in both time-averaged and unsteady aspects. Furthermore, flow control effect at different angles of attack is also investigated. The results show that laminar separation can be effectively restrained, and the lift enhancement and drag reduction are evident.

Design methodology using characteristic parameters control for low Reynolds number airfoils

In the past century, low Reynolds number airfoil design for both military and civil applications has continued to capture the interest of practitioners of applied aerodynamics. A new design methodology for airfoils has been developed, which controls the airfoil profile through 8 parameters. The airfoil aerodynamic characteristics were predicted through the XFOIL code, to optimize airfoil under mode-FRONTIER environment. The reliability verification result predicted that the XFOIL code can be used to determine the airfoil performance in the linear segment of the lift coefficient curve. Application of this methodology was demonstrated through two cases. For Case-I, airfoils design were based on E387 airfoil profile and synthetic aerodynamic performance at different angles of attack for Re=2.0×105 were considered. While for Case-II, designed airfoils were based on PSU 94-097 airfoil with synthetic aerodynamic performance at different angles of attack for Re=4.0×105. Results of both cases showed enhanced aerodynamic properties for the designed airfoils.

Effect of Turbulence Intensity on Low Reynolds Number Airfoil Aerodynamics

The flow transition over the airfoil at low Reynolds number influences its aerodynamic performance; hence this is being studied by many researchers in the recent times. One of the important factors affecting flow transition is the turbulence intensity of the oncoming flow that has not been well addressed. Here a systematic study on a few of Low Reynolds number airfoils is made though viscous- inviscid interaction code XFLR to understand the sensitivity of the inlet turbulence on the flow transition. The analyses with XFLR5 code were made at three Reynolds number and three different turbulent intensity values. The analysis brings out clearly the sensitivity of the flow to turbulent intensity. The reason for the drag increase and scatter in the experimental data has been investigated which is seen in case of E387 airfoil for Reynolds number below 100,000. Â

The Effects of Different Roughness Configurations on Aerodynamic Performance of Wind Turbine Airfoil and Blade

In this research, viscous and turbulent flow is simulated numerically on an E387 airfoil as well as on a turbine blade. The main objective of this paper is to investigate various configurations of roughness to find a solution in order to mitigate roughness destructive impacts. Hence, the sand grain roughness is distributed uniformly along pressure side, suction side and both sides during the manufacturing process. Navier-Stokes equations are discretized by the finite volume method and are solved by SIMPLE algorithm. Results indicated that in contrast with previous studies, the roughness will be useful if it is applied on only pressure side of the airfoil. In this condition, the lift coefficient is increased to and 1.2% compare to the airfoil with rough and smooth sides, respectively. However, in 3-D simulation, the lift coefficient of the blade with pressure surface roughness is less than smooth blade, but still its destructive impacts are much less than of both surfaces roughness and suction surfaces roughness. Therefore, it can be deduced that in order to reveal the influence of roughness, the simulation must be accomplished in three dimensions.Article History: Received Jun 12th 2017; Received in revised form August 27th 2017; Accepted Oct 3rd 2017; Available onlineHow to Cite This Article: Jafari, K., Djavareshkian, M.H., Feshalami, B.H. (2017) The Effects of Different Roughness Configurations on Aerodynamic Performance of Wind Turbine Airfoil and Blade. International Journal of Renewable Energy Development, 6(3), 273-281.https://doi.org/10.14710/ijred.6.3.273-281

An efficient low-speed airfoil design optimization process using multi-fidelity analysis for UAV flying wing

This paper proposes an efficient low-speed airfoil selection and design optimization process using multi-fidelity analysis for a long endurance Unmanned Aerial Vehicle (UAV) flying wing. The developed process includes the low speed airfoil database construction, airfoil selection and design optimization steps based on the given design requirements. The multi-fidelity analysis solvers including the panel method and computational fluid dynamics (CFD) are presented to analyze the low speed airfoil aerodynamic characteristics accurately and perform inverse airfoil design optimization effectively without any noticeable turnaround time in the early aircraft design stage. The unconventional flying wing UAV design shows poor reaction in longitudinal stability. However, It has low parasite drag, long endurance, and better performance. The multi-fidelity analysis solvers are validated for the E387 and CAL2463m airfoil compared to the wind tunnel test data. Then, 29 low speed airfoils for flying wing UAV are constructed by using the multi-fidelity solvers. The weighting score method is used to select the appropriate airfoil for the given design requirements. The selected airfoil is used as a baseline for the inverse airfoil design optimization step to refine and obtain the optimal airfoil configuration. The implementation of proposed method is applied for the real flying-wing UAV airfoil design case to demonstrate the effectiveness and feasibility of the proposed method.

Optimization of drag-reduction by suction using multi-island genetic algorithm

To overcome the drawback of large suction mass requirement,the suction control for drag reduction was optimized. Computational fluid dynamics( CFD) in conjunction with multi-island genetic algorithm was employed as the tool to achieve the optimization. E387 airfoil was employed as the physical model.The suction location and mass flux of slot were set as the design optimization variables. The goal was to minimize both the airfoil drag and suction mass requirement by identifying the optimal suction location on the upper airfoil surface. The results show that the suction location and the suction mass requirement could be optimized by multi-island genetic algorithm. When the suction location is optimal,the mass flux of slot reaches the lower limit of the optimization interval with the airfoil drag reduced up to 8. 3%. The occurrence of transition is not delayed by suction control so that friction drag is not reduced and the airfoil drag reduction is mainly due to the reduction in pressure drag.

Optimization of Suction Control on an Airfoil Using Multi-island Genetic Algorithm

To overcome the disadvantage of large suction requirements, the suction control for drag reduction is optimized. Computational fluid dynamics (CFD), in conjunction with multi-island genetic algorithm (MIGA), is employed to achieve the optimization. An E387 airfoil is employed as the physical model. The suction location and mass flux of a slot are set as the design parameters. The goal is to minimize both the airfoil drag and suction requirement by identifying the optimal suction location on the upper airfoil surface. The effects of different numbers of suction slots were investigated. Results show that the suction control for drag reduction could be optimized using MIGA. For a single-suction slot, the reduction in airfoil drag is up to 8.3%, and the mass flux of a slot reaches the lower limit of the optimization interval. The increase in suction slot number results in a better drag reduction effect, which is accompanied by larger suction requirement and slower convergence. The main reason for airfoil drag reduction is the decrease in the pressure drag.

An Optimization of Wind Turbine Airfoil Possessing Good Stall Characteristics by Genetic Algorithm Utilizing CFD and Neural Network

In this research, an optimization of a wind turbine airfoil is performed by Genetic Algorithm (GA) as optimization method, coupled with CFD (Computational Fluid Dynamics) and Artificial Neural Network (ANN). A pressure-based implicit procedure is applied to solve the Navier-Stokes equations on a nonorthogonal mesh with collocated finite volume formulation to calculate the aerodynamic coefficients. The boundedness criteria for the numerical procedure are determined by Normalized Variable Diagram (NVD) scheme and the k-e eddy-viscosity turbulence model is utilized. ANN has been used as surrogate model to reduce computational cost and time. Single objective and multi objective optimization of wind turbine airfoil have been performed and the results of optimization are presented. To decrease the number of design variables and producing a smooth shaped airfoil, modified Hicks-Henne functions are applied. In this process, the Eppler E387 airfoil has been applied as the base airfoil. The angle of attack varies from 0 to 20 degrees and Reynolds number of the flow is 460000. The presented technique decreases the time of optimization by 99.5%. Moreover, the results manifest the good agreement of trained ANN outputs and CFD simulation. In addition, the Multi-objective optimization can attain the better solutions than single objective to design a wind turbine airfoil with good stall characteristics.

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.