Wortmann FX Research Articles

Use of an optical profilometer to measure the aerodynamic shape and the twist of a wind turbine blade

This study introduces a metrological approach to measure the aerodynamic shape and the twist of a wind turbine blade. The optical profilometer measurement technique used is laser triangulation. A camera records the image of a line projected onto a section of the blade and, by reconstructing the airfoil shape, the twist angular position of the profile with respect to the axial line of the blade is determined. This methodology is applied to test different sections of a Wortmann FX 63-137 airfoil with a length of 1700 mm. The results of the aerodynamic shape and twist angle are quantitatively verified by comparing them with the ideal or design values. The reconstruction process achieved a resolution of 0.06 mm, and measurement errors in the twist angular position were less than 0.1°. The presented method is efficient, accurate, and low cost to evaluate the blade profiles of low-power wind turbines. However, due to its easy implementation, it is expected to be able to measure any full-scale wind blade profile up to several meters in length.

Airfoil Lift Coefficient Optimization Using Genetic Algorithm and IGP Parameterization: Volume 1

The objective of this study is to develop a genetic algorithm that uses the IGP parameterization to increase the lift coefficient (CL) of three airfoils to be used on wings of unmanned aerial vehicles (UAVs). The geometry of three baseline airfoils was modified by developing a genetic algorithm that operates with the IGP parameterization and performs the aerodynamic analysis using XFOIL in the MATLAB environment. Subsequently, a numerical model was made for each baseline and optimized airfoil using a commercial computational fluid dynamics (CFD) code to analyze the behavior of the lift coefficient. An increase in the average CL was obtained for the Eppler 68, MH 70, and Wortmann FX 60-126 airfoils for angles of attack ranging from 0 to 10, obtaining increments of 17.243%, 14.967%, and 10.708%, respectively. Additionally, an average 5.027% uncertainty was obtained in lift coefficient calculations between XFOIL and CFD. The utility of the IGP method and genetic algorithms for parameterizing and optimizing airfoils was demonstrated. In addition, airfoils could be tailored for a specific UAV depending on the mission profile. Volume 2 of this study will include experimental data from wind tunnel.

Numerical analysis on the use of multi-element blades in a horizontal-axis hydrokinetic turbine

The blades of a hydrokinetic turbine have a great impact on its performance due to they are the elements responsible for capturing the kinetic energy from water and transform it into rotational mechanical energy. In this work, numerical analyses on the performance of a multi-element blade section were developed. The lift and drag coefficients (CL and CD, respectively) of the hydrofoils with traditional and multi-element configurations were studied. For this purpose, 2D numerical analyses were conducted by using JavaFoil code. S805, S822, Eppler 420, Eppler 421, Eppler 422, Eppler 423, Eppler 857, Wortmann FX 74-CL5-140, Wortmann FX 74-CL5-140 MOD, Douglas/Liebeck LA203A, Selig S1210, Selig S1223 and UI-1720 profiles were tested. The results indicated that the Eppler 420 multi-element hydrofoil provided high efficiency to the turbine. This was attributed to its higher relationship between the maximum CL and CD (CLmax /CD), which was equal to 47.77, compared to that of the Selig S1223 profile (39.59) and other hydrofoils studied. Therefore, the final optimized blade section selected was an Eppler 420 multi-element hydrofoil with a flap chord length of 70% of that of the main profile. The hydrodynamic and structural designs of the optimized blade section were validated with detailed 3D numerical models, through ANSYs Fluent software. The fluid and structural domains were connected using one-way coupling. The influence of the blade geometry and the operational parameters on the stresses supported by the blades were found by analyzing the fluid-structure interaction. From the numerical analyses conducted, it was observed that the blades did not exhibit structural fails. In this regard, the multi-element hydrofoil might be used for the design of a horizontal-axis hydrokinetic turbine with a high efficiency.

Aerodynamic Characteristics of Flow over Two Unsymmetrical Tandemly Arranged Airfoils – Numerical Simulation

There have been many insects having a tandem wing configuration that gives them a major advantage for maneuvering with various desirable speed, such as dragonflies and butterflies, but subsequently have been used for a wider range of applications. So, it is well known that the tandem airfoil arrangement will have better aerodynamic characteristics than those of the single airfoil arrangement. The present work aims at numerically predicting the aerodynamic characteristics of the single airfoil and tandem airfoil arrangements of the Wortmann FX 63-137 airfoil profile at a Reynolds number of 0.5 x 106. The numerical simulations are performed using commercial CFD software, ANSYS-Fluent. Turbulent flows are modeled using the k-ω RANS model with a second-order upwind scheme. The pressure-velocity coupling is done through the SIMPLE algorithm. In the tandem arrangement, airfoils are positively staggered in the flow direction with variable gaps ranging from 0.1m to 0.7m with an increment of 0.2m and the perpendicular distance between the leading edges of two airfoils is fixed at 0.3 m and simulations are performed for a various angle of attacks with a range of 0 to ± 14°. The aerodynamic characteristics of the single and tandem arrangements of the same airfoil are compared and the effect of wake from the primary airfoil on a secondary airfoil at different angles of attack is also studied for the same conditions.

Letter: A note on flow characterization of the FX63-137 airfoil at low Reynolds number using oil-film interferometry technique

The Wortmann FX 63-137 airfoil has been extensively studied and used in a low Reynolds number flow regime due to its excellent aerodynamic performance with high lift and soft-stall characteristics. In this work, a laminar separation bubble (LSB) on the upper surface of the FX63-137 airfoil is experimentally studied at low Reynolds numbers of 200 000, 300 000, and 500 000 with different angles of attack via the oil-film interferometry (OFI) technique. The flow features, such as laminar separation, reattachment, turbulent separation, and laminar-turbulent transition, on the upper surface were clearly captured. Furthermore, the characteristics of the reverse flow and reattached flow of LSB were also exhibited evidently. Compared with oil flow visualization, the OFI technique is much easier to use, is less time-consuming, and provides for more indistinct flow features over the airfoil surface.

Experiments of Propeller-Induced Flow Effects on a Low-Reynolds-Number Wing

Novel findings are discussed in this paper that will be especially beneficial to designers and modelers of small-scale unmanned air vehicles and high-altitude long-endurance vehicles that both operate at low Reynolds numbers (). Propeller-induced flow effects in both tractor and pusher configurations on a rectangular wing using the Wortmann FX 63-137 airfoil (a common low-Reynolds-number high-lift airfoil) are presented in this paper. Significant performance benefits can be found for a wing in the tractor configuration. Experiments, including trip tests and upper-surface oil flow visualization, show and verify that the propeller slipstream induces early transition to turbulent flow in the regions within the slipstream and the premature formation of a separation bubble in the regions outside the slipstream. The result is a reduction of pressure drag and an increase in lift of the wing where lift-to-drag ratios are as high as 10–12 (a maximum of 70% increase in lift-to-drag ratio from a clean wing configuration) and are measured at both low and high angles of attack up to stall (0–16 deg). Similar performance benefits are not observed in pusher configuration results where only increased local flow velocity and varying inflow angle effects are apparent. Thus, contrary to the design rules for optimal performance of wings at high Reynolds numbers, at low Reynolds numbers, a propeller in the tractor configuration exhibits significant performance improvements, especially in cruise configurations (low angles of attack), as compared with a propeller in the pusher configuration or even a clean wing.

Study on effect of some geometric transformations of the trailing edge of airfoils on their aerodynamic parameters

The work objective is to evaluate how the geometric transformations of the trailing edge of some airfoils affect the aerodynamic characteristics. Such transformations as the trailing edge thickening and rounding are considered. The performance of Wortmann FX 63-137, NACA 23024 и Clark Y is calculated. The effect of the trailing edge changes on their aerodynamic performance at Reynolds numbers from 200,000 to 1,000,000 is assessed. It is shown that the thickening of the trailing edge increases the drag coefficient up to some Reynolds number dependent on the airfoil, and thereafter it reduces. At that the increase of the lift coefficient is observed. The rounding of the trailing edge reduces both the lift and drag forces, and it can lead to the improvement of the airfoil lift-to-drag ratio for certain angles of attack. The data obtained can be used in the manufacture of blades with the profiles discussed.

THE INFLUENCE OF FREE AND DISTURBED LAMINAR-TURBULENT TRANSITION FOR THE WORTMANN FX 66-S-196 V1 AND EPPLER E 385 AIRFOILS AT LOW REYNOLDS NUMBERS

This work was carried out to compare theoretically calculated airfoil characteristics with the published measurements data. Furthermore, in this work the influence of free and disturbed laminar-turbulent transitions was analysed. The calculation of the Wortmann FX 66‑S‑ 196 V1 and Eppler E 385 airfoils was made using three codes: Eppler program system PROFIL, XFOIL and RFOIL. The influence of boundary layer disturbed transition on airfoil was analyzed at low Reynolds numbers. The calculated data were compared with published measurement data. The measurement data were obtained in low-speed, low turbulence wind tunnels of the Department of Aerospace Engineering at the Delft University of Technology and Institute of Aerodynamics and Gasdynamics at Stuttgart University.DOI: http://dx.doi.org/10.5755/j01.mech.19.2.4158

Pitch Stability Analysis of an Airfoil in Ground Effect

The effects of placing a slot through a two-dimensional Wortmann FX 63-137 airfoil in ground effect were examined using computational fluid dynamics. The geometric shape of the slot was varied in three different ways: the width of the slot (w/c = 0.02, 0.04, and 0.06), the angle of the slot with respect to the airfoil's chord line (d = 20, 30, and 40), and the position ofthe slot along the chord line, (x/c = 0.15,0.20, and 0.25). In addition, the airfoil was tested at five different angles of attack: ―3, 0, 5, 10, and 15 deg. The commercially available software Gambit 2.3.16 was used to create the computational grids. FLUENT 6.2.16 with the renormalized group k-e turbulence model was then used to simulate the flow. Pitch stability of the slotted airfoil was examined and results indicated that increasing the angle of attack of the slotted airfoil while in ground effect had a reduced increase in lift when compared with the lift generated by the baseline Wortmann FX 63-137 airfoil. Results also showed that the slot could be used to reduce center-of-pressure movement along the chord of the airfoil for the range of angles of attack investigated, thus improving the overall pitch stability of the airfoil. The slot geometry that produced a minimal center-of-pressure fluctuation was located at 20% of the chord length from the leading edge with a width of 2% and an angle of 20 deg between the slot and a line normal to the chord line.

Shear Stress Measurements on an Airfoil Surface Using Micro-Machined Sensors.

The motivation for this research was to obtain information on the separation characteristics associated with the phenomenon of stall. This separation data will ultimately be utilized as part of an optimum control system to reduce the negative effects associated with stall. Surface shear stress measurements were carried out using MEMS-based sensors on a two-dimensional wing with a Wortmann FX 63-137 airfoil section (chord Reynolds numbers ranged from 1×105 to 6×105). Computational airfoil performance from an airfoil analysis code was compared with the results of measurements. The wall shear stress distribution was measured by five micro hot-film sensors, which were flush mounted on the 2-D wing over the frontal 50% of the chord at various spanwise locations. Hysteresis characteristics were determined from time averaged and rms shear stress values as well as from airfoil performance curves.

Shear Stress Measuremens on an Airfoil Surface Using Micro-Machined Sensors.

The motivation for this research was to obtain information on the separation characteristics associated with the phenomenon of stall. This separation data will ultimately be utilized as part of an optimum control system to reduce the negative effects associated with stall. Surface shear stress measurements were carried out using MEMS-based sensors on a two-dimensional wing with a Wortmann FX 63-137 airfoil section(chord Reynolds numbers ranged from 1×105 to 6×105). Computational airfoil performance from an airfoil analysis code was compared with the results of measurements. The wall shear stress distribution was measured by five micro hot-film sensors, which were flush mounted on the 2-D wing over the frontal 50% of the chord at various spanwise locations. Hysteresis characteristics were determined from time-averaged and rms shear stress values as well as from airfoil performance curves.

Unsteady aerodynamics of a Wortmann wing at low Reynolds numbers

The unsteady effects of turbulence and gusts on the performance of a full-scale Wortmann FX 63-137 wing for remotely piloted vehicle applications were studied by conducting experiments in the atmospheric boundary layer. The wing, which had an aspect ratio of 6, was mounted on an instrumented truck equipped for force/ moment and wind measurements. The vehicle remained stationary, and the wing was aligned with the prevailing wind. The wing experienced predominantly a plunging rather than a pitching motion, together with sweeping and longitudinal oscillations, due to the unsteady three-dimensional wind Held. The chord Reynolds number ranged from 250,000 to 450,000, and the turbulence intensity ranged from 8% to about 20%. From the spectra of the wind components, the reduced frequencies experienced by the wing may be up to 0.1 or higher, indicating that unsteady effects are important. The results show significant lift overshoot, resulting in an increase in the maximum lift coefficient and stall angle. The aerodynamic coefficients do not show pronounced hysteresis loops. A significant reduction of the minimum drag coefficient was also observed, consistent with the theory of a rigidwing plate undergoing plunging oscillation. It was concluded that the fluctuating wind field significantly improved the wing's maneuverability and endurance.

Airfoil boundary layer measurements at low Re in an accelerating flow from a nonzero velocity

The effects of an accelerating freestream from a nonzero velocity on the transitional separation bubble characteristics were investigated quantitatively. Hot wire anemometry was used to determine the boundary layer velocity profile repsonse to the acceleration at selected chordwise locations on a Wortmann FX 63-137 airfoil at 7 ° angle of attack. Both positive and negative accelerations were studied from base chord Reynolds number of 100,000 and 150,000, respectively. The purpose of this experiment was to verify the trends witnessed in previous research concerning a sinusoidally oscillating freestream velocity by uncoupling the accelerating and decelerating boundary layer effects. The experimental results indicate that as a result of a freestream acceleration, the separation bubble position shifts in the direction opposite to the chordwise direction it would move for a quasi-steady velocity change. The transition location was more responsive to the acceleration than was the separation position. This supports the oscillating freestream experiment conclusions.

The effect of trailing edge extensions on the performance of the Göttingen 797 and the Wortmann FX 63-137 aerofoil sections at Reynolds numbers between 3 x 105 and 1 x 106

SummaryThe effect of trailing edge extensions was tested for the twodimensional Göttingen 797 and Wortmann FX 63-137 aerofoil sections with smooth surfaces at chord Reynolds numbers from 3 x 105 to 1 x 106 in the 8ft x 6ft low speed wind-tunnel at the Cranfield Institute of Technology. Force measurements were made on the basic aerofoil sections and with extension plates of 10% and 20% chord set tangential to the upper surface at the trailing edge. It was verified that the addition of an extension plate effectively brings about an increase of maximum lift coefficient and an improved lift-to-drag ratio for the Göttingen aerofoil section. However, the effect of the extension plate was small on the Wortmann aerofoil section.

The effect of trip wire roughness on the performance of the Wortmann FX 63-137 airfoil at low Reynolds numbers

An experimental investigation was conducted on the performance and boundary layer characteristics of the Wortmann FX 63-137 airfoil with and without trip wire roughness. Data were obtained through use of a three-component strain gage force balance and static pressure measurement equipment at a test Reynolds number of R c = 100,000. Emphasis was placed on determining the effect of trip wire placement and size on such performance parameters as (C l /C d )max and (C 3/2 /C d )max. Prediction of transition location by the criterion due to Tani and Gibbings was found to have limited application. Most trip wire locations resulted in degraded performance, but for some locations, minimum drag was reduced, maximum lift to drag ratio increased, and hysteresis averted.