Gurney Flap Research Articles

Spectral and wavelet analysis in the wake of an airfoil with Gurney flap

In this work we identify the coherent vortices in the leeward wake of an HQ 17 airfoil with a Gurney flap. This high-lift device consists of a small plate perpendicular to the airfoil, at or near the trailing edge, with a height � of the order from 1% to 4% of the chord. The overall effect is to produce a significant increase in lift, together with a relatively minor increase in airfoil drag. Its geometry generates vortex shedding of spatial scale H, which modulates the wake and thus influence the global configuration of the flow. A numerical study was performed with the commercial software ANSYS Fluent. Simultaneously, experiments were carried out in the wind tunnel of the Aeronautical Departmental Area from the Engineering School of the National University of La Plata. With a Dantec StreamLine hot-wire anemometer, records of the instantaneous horizontal and vertical velocity components in the airfoil wake were obtained. Both the experimental data and those obtained by numerical simulation were analyzed with the continuous wavelet transform technique, in order to identify and characterize the coherent vortices in the wake. Results show the shed vortices structure and the organization degree of this periodic shedding.

Unsteady RANS-based DMD analysis of airfoil NACA0015 with Gurney flap

The present investigation summarizes the numerical prediction and DMD analysis of the flow in the vicinity of a Gurney flap set on an airfoil NACA0015 at Re = 10,300 tested in a water tunnel with time-resolved Particle Image Velocimetry. A series of two-dimensional U-RANS simulations has been accomplished using an incompressible, time-accurate solver of OpenFOAM. A purely data-based DMD analysis has followed to extract the spatio-temporal coherent structures from the time-evolving flowfields, to mimic the experiments. It is stressed that this work focuses on the analysis of this kind of flap by applying DMD to datasets generated with numerical simulations, which has not been previously investigated, but using experimental datasets. Under this approach, the comparison of the numerics with the experimental counterpart shows a remarkable agreement for both the structures and major frequencies, which stresses the suitability of the incompresible U-RANS approach in this class of studies. Special attention has been focused on the modelling of the experimental facility, and a quantification of the prediction accuracy is provided by assessing the deviation of the spectral content. The simulations clearly show the key role of having a good characterization of the water tunnel to be successful at capturing the spectrum and flow unsteadiness. Furthermore, they reveal quite promising for those industrial oriented simulations, which deal with lift-enhancement devices and lift-to-drag ratio optimization of airfoils since they permit an accurate prediction.

Experimental investigation into the flow structure of plasma induced Jet in a 2-D Cross-Flow

This study is focused on the flow physics in the condition of employing the active flow control methods and DBD plasma actuators as a transverse jet. In the current research, a single DBD plasma actuator is added to the Trailing Edge of a flat plate model and several wind tunnel experiments are conducted to study the flow structures. The salient goal of this work is to investigate the flow physics of Plasma Jet in Cross-Flow. Wind tunnel experiments results in two different free stream velocities of U∞=10m/sandU∞=20m/s and several model’s angles of attack show that the flow domain consists of two different counter rotating vortices at St=0.1886 and 0.1725 and a secondary vortex with St=0.5842. The manner of these vortices in the different AoA and free stream velocities, and also the shape of the velocity profile in the near wake and far-field wake of the plasma jet prove that the flow domain around the Plasma Jet in Cross-Flow is very similar to the flow around an airfoil equipped with Gurney Flap.

Review of experimental investigations of wings in ground effect at low Reynolds numbers

The ground effect-induced large lift increase and lift-induced drag reduction have long been recognized and utilized in the design and construction of wing-in-ground effect (WIG) craft. Various wing planforms have been employed in WIG craft. In this study, the experimental investigations of rectangular wings and delta wings of reverse and regular configurations at low Reynolds numbers are reviewed. For rectangular wings, both chord-dominated and span-dominated ground effects on the aerodynamics, tip vortex, and lift-induced drag are reviewed. For reverse delta wings, in addition to the experimental measurements of the aerodynamics and tip vortex flow at different ground distances, passive flow control utilizing Gurney flap, cropping, and anhedral are reviewed. The impact of ground effect on delta wings is also discussed. Suggestions for future investigations applicable to each wing planform in-ground effect are provided.

Characterization of the low-noise drone propeller with serrated Gurney flap

Drones, which have become increasingly popular in recent years, produce a lot of noise due to the movement of their propellers. When flying near humans, especially as in urban situations, noise suppression is critical. It has been demonstrated that noise can be minimized by increasing propeller lift per unit rotation speed and decreasing propeller rotation speed by expanding propeller area or designing the airfoil shape. This study developed a new structure, serrated Gurney flap, by merging the Gurney flap, which is the trailing-edge structure of an airfoil, and the serration, which is the low-noise structure found in an owl feather, and studied its performance through experiments and numerical simulations. The results indicated that the structure can boost the propeller’s lift coefficient while reducing the vortex separation induced by the Gurney flap and suppress propeller noise by slowing the propeller. Further modification of its structure may result in improved efficiency as well as decreased noise level.

Numerical investigation of flow control in low-pressure turbine cascade using Gurney Flaps

Abstract This paper reports the numerical investigations to analyze the effect of the application of Gurney Flaps on various configurations in a Low-Pressure Turbine (LPT) cascade in mitigating the laminar flow separation during low Reynolds number operations. T106 LPT blade of chord 60 mm has been selected for the present study. Gurney Flaps of flat type and quarter round type of a particular height of the chord length are selected. Flaps are provided near the blades’ trailing edges for numerical analysis. The numerical computations are performed using STARCCM+ software, and the K-ω SST turbulence Model is used for turbulence closure. The studies are performed at various Reynolds numbers ranging from 37,500 to 138,750 to understand the application of various configurations of Gurney Flap vis a vis turbine blade without Gurney Flap. Performance parameters such as lift coefficient, drag coefficient, aerodynamic efficiency, and static pressure distributions over the blade surface are used to analyse the alterations in the performance of aerodynamic characteristics of the LPT Blade. All the Gurney Flap configurations improved the overall blade aerodynamics. Among these configurations, the flat Gurney Flap configuration is found to be superior as it improves the aerodynamic efficiency of the blade.

Numerical investigation of flow control in low-pressure turbine cascade using Gurney Flaps

Abstract This paper reports the numerical investigations to analyze the effect of the application of Gurney Flaps on various configurations in a Low-Pressure Turbine (LPT) cascade in mitigating the laminar flow separation during low Reynolds number operations. T106 LPT blade of chord 60 mm has been selected for the present study. Gurney Flaps of flat type and quarter round type of a particular height of the chord length are selected. Flaps are provided near the blades’ trailing edges for numerical analysis. The numerical computations are performed using STARCCM+ software, and the K-ω SST turbulence Model is used for turbulence closure. The studies are performed at various Reynolds numbers ranging from 37,500 to 138,750 to understand the application of various configurations of Gurney Flap vis a vis turbine blade without Gurney Flap. Performance parameters such as lift coefficient, drag coefficient, aerodynamic efficiency, and static pressure distributions over the blade surface are used to analyse the alterations in the performance of aerodynamic characteristics of the LPT Blade. All the Gurney Flap configurations improved the overall blade aerodynamics. Among these configurations, the flat Gurney Flap configuration is found to be superior as it improves the aerodynamic efficiency of the blade.

Numerical study on aerodynamic performance and noise of wind turbine airfoils with serrated gurney flap

Improving the airfoil aerodynamics of wind turbines is an effective way to raise the wind energy utilization rate and reduce the dependence on fossil fuels. Select a NACA0018 airfoil as a baseline, and a novel serrated Gurney flap (SGF) is proposed to promote the aerodynamic performance of the airfoil. The SST k-ω turbulence model and large eddy simulation are used to numerically simulate the performance of airfoils with Gurney flap (GF) and SGF. The influence of serration geometry parameters on aerodynamics and noise is examined, and the vortex structure is explored to reveal the inherent mechanism. The results show that the SGFs can significantly improve lift coefficient, delay the stall, and greatly reduce the acoustic noise at investigated attack angles. The arrangement of SGF enhances the stability of shedding wakes and lowers the energy losses, leading to better aerodynamic performance and lower noise. ASGF-0.8-6.7 is a preferred scheme for raising airfoil performance with an enhanced lift-to-drag ratio of 8.61%, a delayed attack angle of the stall of 3°, and a maximum noise reduction of 10.2 dB in the radiated noise, compared to the baseline.

Plasma Gurney Flap Flight Control at Low Angle of Attack

A flight control concept without movable surfaces using electrofluidic actuators is assessed from low-speed scaled two-dimensional (2-D) rectangular wings up to three-dimensional (3-D) full-scale tapered swept wings at realistic aircraft operating conditions. The plasma Gurney flap concept consists of placing spanwise dielectric barrier discharge (DBD) plasma actuators on both sides of a wing or empennage near the trailing edge, and pointing in opposite directions, to change the flow curvature in this region, thus altering lift. Low-speed wind-tunnel tests and corresponding computational fluid dynamics (CFD) simulations are first carried out for this concept on scaled 2-D rectangular wings. Measured lift moment and flow streamlines are used to validate the simulation (CFD) tool. Simulations with this tool are then performed to assess the effect of wing taper and sweep on the effectiveness of the concept at low speed and to evaluate the concept for full-scale 3-D tapered swept-wing geometries for a single-aisle airliner. The results indicate that the plasma Gurney flap has better performance on tapered and swept wings relative to rectangular wings because of the reduction in the velocity component normal to the plasma actuator. Moreover, the presence of shocks at cruise flight conditions improves the effectiveness of the plasma Gurney flap concept.

Performance assessment of a modified wells turbine using an integrated casing groove and Gurney flap design for wave energy conversion

The present study investigates the effect of a triangular casing groove depth and width on Wells turbine performance. Furthermore, it presents an integrated method to boost the power produced by the Wells turbine and delay the stall. This integrated method is implemented by combining the effect of the triangular casing groove with a rectangular Gurney flap (GF). The Gurney flap (GF) increases the lift coefficient by modifying the Kutta condition at the trailing edge. At the same time, the triangular casing groove improves the flow near the blade tip, leading to a delay in the stall inception. The Wells turbine performance is evaluated by solving numerically 3D incompressible Reynolds-Averaged Navier-Stokes equations. To solve the flow characteristics through the turbine, an SST k-ω turbulence model is used, which is validated and verified using previous experimental and numerical works. The results proved that the Wells turbine average torque coefficient increased by 81.11% when using a triangular casing groove and a rectangular Gurney flap. Moreover, the stall inception is delayed from a flow coefficient of 0.225–0.350, which increases the operating range by 55.50% and reduces the maximum efficiency compared with the conventional Wells turbine.

Aerodynamic Characteristics of Ahmed Body with Inverted Airfoil Eppler 423 and Gurney Flap on Fastback Car

The installation of aerodynamic devices, such as rear wings with the application of a Gurney flap, is very important to improve the performance of vehicles and can generate downforce and reduce slip when a car turns and brakes. The goal of this study was to determine the aerodynamic characteristics of the addition of a rear wing using an Eppler 423 airfoil, which was applied with a Gurney flap featuring variations in the angle of attack and the height of the Gurney flap. The rear wing was mounted on the Ahmed body with a rear slant angle of 15°, which is similar to the configuration on a fastback type car. This research was conducted by 3D modeling through computational fluid dynamics (CFD) simulation using ANSYS Student R18.2 by using ahmed body design. There are three variations in the angle of attack for the rear wing (0°, 7.5°, and 15°), as well as five variations in Gurney flap height of 0%, 0.5%, 1%, 1.5%, and 2% for the chord-line length. In this study, the best variation was found at an angle of attack of 15⁰ with a height of 2% C. From this configuration improved CL/CD ratio by 25.36% when compared to the results without a Gurney flap.

Numerical Investigation of Aerodynamic Characteristics of Supercritical RAE2822 Airfoil with Gurney Flap

Gurney flap (GF) is well-known as one of the most attractive plain flaps because of the simple configuration and effectiveness in improving the lift of the airfoil. Many studies were conducted, but the effects of GF on the various airfoil types need to be further investigated. This study aimed to clarify the effect of GF in the case of the supercritical airfoil RAE2822. This research includes a steady, two-dimensional computational investigation carried out on the supercritical airfoil type RAE-2822 to analyze Gurney flap (GF) effects on the aerodynamic characteristics of this type of airfoil utilizing the Spalart-Allmaras turbulence model within the commercial software Fluent. The airfoil with the Gurney flap was analyzed for three different height values 1%c, 2%c, and 3%c, and five mounting angles (30°,45°,60°,75°, and 90°) with the axial chord for angles of attack (-1°,-2°,-3°,0°,1°,2°,3°). The calculations showed that when GF height is increased, the maximum suction pressure on the upper surface increases by 25.4%, 36.5%, and 68.83% when the height of the Gurney flap is 1%c, 2%c, and 3%c, respectively, compared with that on the airfoil without GF. The lift coefficient was also increased, and the shock waves moved downward by increasing GF height. As Gurney flap heights increase, the drag coefficient increases gradually for positive angles of attack but for negative angles of attack. The drag coefficient also decreases with increasing the GF heights. As long as the angle of the mounting is between 45o and 90o, the lift coefficient does not differ on a large scale. For mounting angles less than 45o, the lift coefficient drops quite fast. As a result, reducing the Gurney flap’s lift enhancement and the drag coefficient increases gradually for positive angles of attack, but for negative angles, it can be noted that the drag coefficient decreases with increasing the mounting angles of GF. The calculated values of the lift and drag coefficients with an attack angle and pressure coefficient compared with the experimental values, and a good agreement was noticed.

CNN-based flow control device modelling on aerodynamic airfoils

Wind energy has become an important source of electricity generation, with the aim of achieving a cleaner and more sustainable energy model. However, wind turbine performance improvement is required to compete with conventional energy resources. To achieve this improvement, flow control devices are implemented on airfoils. Computational fluid dynamics (CFD) simulations are the most popular method for analyzing this kind of devices, but in recent years, with the growth of Artificial Intelligence, predicting flow characteristics using neural networks is becoming increasingly popular. In this work, 158 different CFD simulations of a DU91W(2)250 airfoil are conducted, with two different flow control devices, rotating microtabs and Gurney flaps, added on its Trailing Edge (TE). These flow control devices are implemented by using the cell-set meshing technique. These simulations are used to train and test a Convolutional Neural Network (CNN) for velocity and pressure field prediction and another CNN for aerodynamic coefficient prediction. The results show that the proposed CNN for field prediction is able to accurately predict the main characteristics of the flow around the flow control device, showing very slight errors. Regarding the aerodynamic coefficients, the proposed CNN is also capable to predict them reliably, being able to properly predict both the trend and the values. In comparison with CFD simulations, the use of the CNNs reduces the computational time in four orders of magnitude.

Experimental investigation of mini Gurney flaps in combination with vortex generators for improved wind turbine blade performance

Abstract. This wind tunnel study investigates the aerodynamic effects of mini Gurney flaps (MGFs) and their combination with vortex generators (VGs) on the performance of airfoils and wind turbine rotor blades. VGs are installed on the suction side aiming at stall delay and increased maximum lift. MGFs are thin angle profiles that are attached at the trailing edge in order to increase lift at pre-stall operation. The implementation of both these passive flow control devices is accompanied by a certain drag penalty. The wind tunnel tests are conducted at the Hermann-Föttinger Institut of the Technische Universität Berlin based on two airfoils that are characteristic of different sections of large rotor blades. Lift and drag are determined using a force balance and a wake rake, respectively, for static angles of attack between −5 and 17∘ at a Reynolds number of 1.5 million. The impact of different MGF heights including 0.25 %, 0.5 % and 1.0 % and a VG height of 1.1 % of the chord length is tested and evaluated. Furthermore, the clean and the tripped baseline cases are considered. In the latter, leading-edge transition is forced with Zig Zag (ZZ) turbulator tape. The preferred configurations are the smallest MGF on the NACA63(3)618 and the medium-sized MGF combined with VGs on the DU97W300. Next, the experimental lift and drag polar data are imported into the software QBlade in order to design a generic rotor blade. The blade performance is simulated with and without the add-ons by means of two case studies. In the first case, the retrofit application on an existing blade mitigates the adverse effects of the ZZ tape. Stall is delayed and the aerodynamic efficiency is partly recovered leading to an improvement of the power curve. In the second case, the new design application allows for the design of a more slender blade while maintaining the rotor power. This alternative blade appears to be more resistant against the adverse effects of forced leading-edge transition.

On the combined use of Vortex Generators and Gurney Flaps for turbine airfoils

While Vortex Generators (VGs) and Gurney Flaps (GFs) are commonly used for airfoil flow control, studies of a combination of the two devices are rare. The present investigation aims at examining the combined effect of VGs and GFs on a 20% thick airfoil. To this end, a wind tunnel investigation coupled with a computational study was performed. The present paper presents force, pressure and Stereo Particle Image Velocimetry measurements, along with Unsteady Reynolds Averaged Navier Stokes simulations.

Potential of Mini Gurney Flaps as a Retrofit to Mitigate the Performance Degradation of Wind Turbine Blades Induced by Erosion

Leading edge erosion of wind turbine blades is still an important challenge for wind energy professionals, both at research and industrial level. While the efficiency and durability of materials and coatings are improving rapidly, it is important to explore innovative solutions at the aerodynamic design level to mitigate the adverse effects of surface erosion. For that, a preliminary analysis on the use of Mini Gurney Flaps (MGFs) is presented in the study. High-fidelity Computational Fluid Dynamic (CFD) simulations are used to evaluate the impact of severe leading edge (LE) erosion on the performance of the FFAW3-241 airfoil on the rotor blade of the DTU 10-MW Reference Wind Turbine, which is used as test case. CFD lift and drag polars of the eroded airfoil show that MGFs are able to partially recover aerodynamic efficiency caused by erosion; this suggested evaluating their use as a retrofit solution for blades that already experienced leading edge erosion damage. When tested on the DTU 10MW RWT blade, results show how, if sized correctly, MGFs perform as predicted: the lift curve is shifted back to its design value and performance is improved with respect to the eroded blade. Moreover, as one would expect, higher than optimal MGFs resulted in excessive lift increases and thus decreased performance, even in the case of LE-erosion. Although these devices behave as intended however, based on the results of this paper, performance decreases are noted at high tip-speed-ratios (TSR), due to the blade operating in off-design conditions.

Numerical investigation of the benefits of serrated Gurney flaps on an axial flow fan

A novel serrated Gurney flap (SGF) is proposed, and a large eddy simulation is employed to simulate a two-stage variable-pitch axial fan with SGFs. The influence of the novel blades on the aerodynamic performance, sound characteristics and internal dynamics of the fan was examined, and the possible mechanism for noise reduction and vortex structure were investigated. Results indicate that the peak efficiency of the fan shifts toward the large flowrate side, and the high-efficiency region is widened when using SGFs. SGFs with an appropriate serration height reduce high-frequency noise, and the noise reduction gradually improves with decreasing serration height. The use of SGFs decreases the turbulence pulsation intensity, improves the size and distribution of wake vortices, and abates the leading-edge separation vortex and turbulence intensity. Mechanism studies indicate that two counter-rotating vortex pairs in the vertical and horizontal directions interact strongly, which alleviates the aerodynamic acoustics of the fan. A fan with an SGF with a serration height of 0.8% chord achieves the optimal overall performance, including improved efficiency, total pressure rise, and reduced noise.

High-Reynolds-number wind turbine blade equipped with root spoilers – Part 1: Unsteady aerodynamic analysis using URANS simulations

Abstract. A commercial wind turbine blade equipped with root spoilers is analysed using 2D URANS computational fluid dynamics (CFD) to assess the unsteady impact of passive devices. In this work, we present the 2D CFD unsteady results from a non-rotating single thick section located at the root end of the blade with and without spoiler. Computations were performed at the chord-based Reynolds number Rec=3×106. The analysed spoiler is of commercial size with a height of approximately 33 % of the local chord. Comparing to existing literature, it is at least 1 order of magnitude larger than the size of the well-known Gurney flaps. The analysis is first performed in the steady state at a single angle of attack using global aerodynamic forces, the local pressure distributions, and flow field analysis. Analyses are then continued accounting for the flow unsteadiness. The spoiler induces an important wake behaviour linked to the apparition of global load fluctuations. Using the wall pressure distributions and the associated spatio-temporal organisation of the flow field, those fluctuations are well characterised. Globally, in terms of lift gain, adding a spoiler is found to be detrimental for the negative angles of attack while of high interest for higher angles of attack. Another drawback of the spoiler addition is the unsteady effects. A dominant peak frequency is emerging in the aerodynamic polar coefficients, when adding a spoiler, which corresponds to a vortex shedding organisation.

Aerodynamic Optimization and Analysis of Low Reynolds Number Propeller with Gurney Flap for Ultra-High-Altitude Unmanned Aerial Vehicle

Ultra-high-altitude unmanned aerial vehicles have created a high demand for the performance of propellers under low Reynolds numbers, while the efficiency of such propellers by the existing design framework has reached a bottleneck. This paper explores the possibility of extending the Gurney flap on low Reynolds number propellers to achieve efficiency breakthrough. An iterative optimization strategy for propellers with Gurney flaps is established, in which cross-sectional airfoils can be continuously optimized under updated Reynolds numbers and lift coefficients. A computational fluid dynamics (CFD) simulation based on the γ-Reθ model was used as an aerodynamic analysis method. Propellers with and without Gurney flaps were optimized successively. Optimal results were analyzed using the CFD method. Results showed that an optimal propeller with a Gurney flap can achieve an efficiency of 82.0% in cruising conditions, which is 1.8% higher than an optimal propeller without a Gurney flap. Compared with the latter, the consumed power of the optimal propeller with a Gurney flap can be reduced by 2.2% with the same advance speed. Furthermore, the variation of the improvement by the Gurney flap propeller, along with its Reynolds number, was studied. A wind tunnel test indicates that the performance of the propellers obtained by the CFD method are in good agreement with the test results.

Experimental Study of a Gurney Flap on a Pitching Wind Turbine Airfoil under Turbulent Flow Conditions

The present work aimed to investigate the aerodynamic characteristics of a pitching wind turbine airfoil with a Gurney flap under turbulent inflow. Experiments were carried out for the DTU-LN221 offshore wind turbine airfoil under different turbulence levels at Reynolds number 105 order of magnitude by replacing the grilles in the wind tunnel. The dynamic stall characteristics were analyzed by measuring surface pressure and near-wake flow field. The pressure results demonstrated that with the increase of turbulence intensity, the differences in lift hysteresis loops between baseline airfoil and flapped airfoil became smaller. With the turbulence intensity from 0.5% to 10.18%, the maximum lift increment of the Gurney flap decreased from 14.32% to 4.34% (i.e., 0–20° pitching oscillation). In a more extensive range of oscillation, the capability for the lift-improvement dropped down a bit more (i.e., 0–25°). A brief aerodynamic damping analysis indicated that the Gurney flap was more stable in turbulent conditions than the baseline airfoil. Besides, hysteresis loops of the wake were analyzed to compare the difference between the flapped airfoil and the baseline airfoil. Unlike the studies of static airfoils, the results may help better understand the dynamic characteristics of offshore wind turbines with Gurney flaps for practical situations.