Numerical Investigation of Surface Curvature Effects on Aerofoil Aerodynamic Performance

2015 ◽  
Vol 798 ◽  
pp. 589-595 ◽  
Author(s):  
Xiang Shen ◽  
Theodosios Korakianitis ◽  
Eldad Avital
Keyword(s):  
Separation Bubble ◽  
Circle Method ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Surface Curvature ◽  
Operating Conditions ◽  
Curvature Effects ◽  
Curvature Continuity ◽  
Curvature Distribution

The prescribed surface curvature distribution blade design (CIRCLE) method optimises aerofoils and blades by controlling curvature continuity and slope of curvature distribution along their surfaces. The symmetrical NACA0012 exhibits a surface curvature discontinuity at the leading edge point, and the non-symmetrical E387 exhibits slope-of-curvature discontinuities in the surface. The CIRCLE method is applied to both aerofoils to remove both surface curvature and slope-of-curvature discontinuities. Computational fluid dynamics analyses are used to investigate the curvature effects on aerodynamic performance of the original and modified aerofoils. These results are compared with experimental data obtained from tests on the original aerofoil geometry. The computed aerodynamic advantages of the modified aerofoil are analysed in different operating conditions. The leading edge singularity of NACA0012 is removed and it is shown that the surface curvature discontinuity affects the aerodynamic performance near the stalling angle of attack. The discontinuous slope-of-curvature distribution of E387 influences the size of the laminar separation bubble at lower Reynolds numbers, and it affects the inherent profile of the aerofoil at higher Reynolds numbers. It is concluded that the surface curvature distribution of aerofoils has a significant effect on aerofoil aerodynamic performance, which can be improved by redesigning the surface curvature distribution of the original aerofoil geometry.

scholarly journals Computational methods for investigation of surface curvature effects on airfoil boundary layer behavior

2016 ◽  
Vol 11 (1) ◽  
pp. 68-82 ◽  
Author(s):  
Xiang Shen ◽  
Eldad Avital ◽  
Mohammad Amin Rezaienia ◽  
Gordon Paul ◽  
Theodosios Korakianitis
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Surface Curvature ◽  
Operating Conditions ◽  
Laminar Separation ◽  
Curvature Effects ◽  
Computational Fluid Dynamics Analysis ◽  
Layer Behavior ◽  
Curvature Distribution

This article presents computational algorithms for the design, analysis, and optimization of airfoil aerodynamic performance. The prescribed surface curvature distribution blade design (CIRCLE) method is applied to a symmetrical airfoil NACA0012 and a non-symmetrical airfoil E387 to remove their surface curvature and slope-of-curvature discontinuities. Computational fluid dynamics analysis is used to investigate the effects of curvature distribution on aerodynamic performance of the original and modified airfoils. An inviscid–viscid interaction scheme is introduced to predict the positions of laminar separation bubbles. The results are compared with experimental data obtained from tests on the original airfoil geometry. The computed aerodynamic advantages of the modified airfoils are analyzed in different operating conditions. The leading edge singularity of NACA0012 is removed and it is shown that the surface curvature discontinuity affects aerodynamic performance near the stalling angle of attack. The discontinuous slope-of-curvature distribution of E387 results in a larger laminar separation bubble at lower angles of attack and lower Reynolds numbers. It also affects the inherent performance of the airfoil at higher Reynolds numbers. It is shown that at relatively high angles of attack, a continuous slope-of-curvature distribution reduces the skin friction by suppressing both laminar and turbulent separation, and by delaying laminar-turbulent transition. It is concluded that the surface curvature distribution has significant effects on the boundary layer behavior and consequently an improved curvature distribution will lead to higher aerodynamic efficiency.

scholarly journals Force and flowfield measurements to understand unsteady aerodynamics of cycloidal rotors in hover at ultra-low Reynolds numbers

2019 ◽  
Vol 11 ◽  
pp. 175682931983367
Author(s):  
Carolyn M Reed ◽  
David A Coleman ◽  
Moble Benedict
Keyword(s):  
Separation Bubble ◽  
Fluid Dynamic ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Dynamic Stall ◽  
Static Case ◽  
Low Reynolds Numbers ◽  
Curvature Effects ◽  
Low Reynolds

This paper provides a fundamental understanding of the unsteady fluid-dynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Re ∼ 18,000) by utilizing a combination of instantaneous blade force and flowfield measurements. The dynamic blade force coefficients were almost double the static ones, indicating the role of dynamic stall. For the dynamic case, the blade lift monotonically increased up to ±45° pitch amplitude; however, for the static case, the flow separated from the leading edge after around 15° with a large laminar separation bubble. There was significant asymmetry in the lift and drag coefficients between the upper and lower halves of the trajectory due to the flow curvature effects (virtual camber). The particle image velocimetry measured flowfield showed the dynamic stall process during the upper half to be significantly different from the lower half because of the reversal of dynamic virtual camber. Even at such low Reynolds numbers, the pressure forces, as opposed to viscous forces, were found to be dominant on the cyclorotor blade. The power required for rotation (rather than pitching power) dominated the total blade power.

Aerodynamic Improvements of Wind-Turbine Airfoil Geometries With the Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method

2011 ◽  
Author(s):  
T. Korakianitis ◽  
M. A. Rezaienia ◽  
I. A. Hamakhan ◽  
E. Avital ◽  
J. J. R. Williams
Keyword(s):  
Wind Turbine ◽  
Stagnation Point ◽  
Surface Pressure ◽  
Turbine Blades ◽  
Circle Method ◽  
Aerodynamic Performance ◽  
Surface Curvature ◽  
Blade Design ◽  
Drag Coefficients ◽  
Curvature Distribution

The prescribed surface curvature distribution blade design (CIRCLE) method can be used for the design of two-dimensional (2D) and three-dimensional (3D) turbomachinery blade rows with continuous curvature and slope of curvature from leading edge (LE) stagnation point to trailing edge (TE) stagnation point and back to the LE stagnation point. This feature results in smooth surface pressure distribution airfoils with inherently good aerodynamic performance. In this paper the CIRCLE blade design method is modified for the design of 2D isolated airfoils. As an illustration of the capabilities of the method, it is applied to the redesign of two representative airfoils used in wind turbine blades: the Eppler 387 airfoil; and the NREL S814 airfoil. Computational fluid dynamic analysis is used to investigate the design point and off-design performance of the original and modified airfoils, and compare with experiments on the original ones. The computed aerodynamic advantages of the modified airfoils are discussed. The surface pressure distributions, drag coefficients, and lift-to-drag coefficients of the original and redesigned airfoils are examined. It is concluded that the method can be used for the design of wind turbine blade geometries of superior aerodynamic performance.

Effects of Curvature Continuity of Compressor Blade Profiles on Their Performances

2014 ◽  
Author(s):  
Yin Song ◽  
Chunwei Gu
Keyword(s):  
Separation Bubble ◽  
Leading Edge ◽  
Optimization Method ◽  
Surface Curvature ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Boundary Layer Equations ◽  
Pressure Spike ◽  
Curvature Continuity ◽  
Continuous Curvature

Curvature discontinuity may exist in the surface, especially at the leading edge, of a compressor blade. The importance of curvature continuity or discontinuity has been realized, but its definite influences and mechanisms still need research. In this paper, an optimization method is proposed to design continuous-curvature blade profiles from datum blades, and a Reynolds-Averaged Navier-Stokes (RANS) solver with a transition model is used to examine the flowfields and performances of different blade profiles. Large eddy simulations of several cases are also presented to validate the RANS results. The effects of leading-edge-blend-point curvature continuity and the main-surface curvature continuity are studied separately. The results show that the curvature continuity at the leading-edge blend point helps to eliminate the separation bubble, and thus improves the blade performance. The main-surface curvature continuity is also found beneficial, although its effects are much smaller than those of the blend-point curvature continuity. Boundary-layer equations of the blade profiles are analyzed in terms of order of magnitude to further study the different curvature-continuity effects of the blend point and main surface theoretically. The analysis reveals the physical facts that produce the pressure spike around a leading-edge blend point with a discontinuous curvature, and thus explains how the optimized continuous-curvature leading edge removes the pressure spike and the related separation. The analysis also finds that the high spike appearing near the nose of a continuous-curvature leading edge at larger incidences is controlled by the large nose curvature rather than curvature discontinuity. The dual separation mechanisms also help to solve the so-called sharp leading edge paradox.

Aerodynamic Improvements of Wind-Turbine Airfoil Geometries With the Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method

2012 ◽  
Vol 134 (8) ◽  
Author(s):  
T. Korakianitis ◽  
M. A. Rezaienia ◽  
I. A. Hamakhan ◽  
E. J. Avital ◽  
J. J. R. Williams
Keyword(s):  
Wind Turbine ◽  
Stagnation Point ◽  
Surface Pressure ◽  
Turbine Blades ◽  
Circle Method ◽  
Aerodynamic Performance ◽  
Surface Curvature ◽  
Blade Design ◽  
Drag Coefficients ◽  
Curvature Distribution

The prescribed surface curvature distribution blade design (CIRCLE) method can be used for the design of two-dimensional (2D) and three-dimensional (3D) turbomachinery blade rows with continuous curvature and slope of curvature from leading edge (LE) stagnation point to trailing edge (TE) stagnation point and back to the LE stagnation point. This feature results in smooth surface pressure distribution airfoils with inherently good aerodynamic performance. In this paper the CIRCLE blade design method is modified for the design of 2D isolated airfoils. As an illustration of the capabilities of the method, it is applied to the redesign of two representative airfoils used in wind turbine blades: the Eppler 387 airfoil and the NREL S814 airfoil. Computational fluid dynamic analysis is used to investigate the design point and off-design performance of the original and modified airfoils, and compare with experiments on the original ones. The computed aerodynamic advantages of the modified airfoils are discussed. The surface pressure distributions, drag coefficients, and lift-to-drag coefficients of the original and redesigned airfoils are examined. It is concluded that the method can be used for the design of wind turbine blade geometries of superior aerodynamic performance.

Two- and Three-Dimensional Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method for the Design of High Efficiency Turbines, Compressors, and Isolated Airfoils

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
T. Korakianitis ◽  
M. A. Rezaienia ◽  
I. A. Hamakhan ◽  
A. P. S. Wheeler
Keyword(s):  
Turbine Blade ◽  
High Efficiency ◽  
Turbine Blades ◽  
Circle Method ◽  
Three Dimensional ◽  
Leading Edge ◽  
Surface Curvature ◽  
Blade Design ◽  
Compressor Blades ◽  
Curvature Distribution

The prescribed surface curvature distribution blade design (CIRCLE) method is presented for the design of two-dimensional (2D) and three-dimensional (3D) blades for axial compressors and turbines, and isolated blades or airfoils. The original axial turbine blade design method is improved, allowing it to use any leading-edge (LE) and trailing-edge (TE) shapes, such as circles and ellipses. The method to connect these LE and TE shapes to the remaining blade surfaces with curvature and slope of curvature continuity everywhere along the streamwise blade length, while concurrently overcoming the “wiggle” problems of higher-order polynomials is presented. This allows smooth surface pressure distributions, and easy integration of the CIRCLE method in heuristic blade-optimization methods. The method is further extended to 2D and 3D compressor blades and isolated airfoil geometries providing smooth variation of key blade parameters such as inlet and outlet flow angles, stagger angle, throat diameter, LE and TE radii, etc. from hub to tip. One sample 3D turbine blade geometry is presented. The efficacy of the method is examined by redesigning select blade geometries and numerically evaluating pressure-loss reduction at design and off-design conditions from the original blades: two typical 2D turbine blades; two typical 2D compressor blades; and one typical 2D isolated airfoil blade geometries are redesigned and evaluated with this method. Further extension of the method for centrifugal or mixed-flow impeller geometries is a coordinate transformation. It is concluded that the CIRCLE method is a robust tool for the design of high-efficiency turbomachinery blades.

Two- and Three-Dimensional Prescribed Surface Curvature Distribution Blade Design (CIRCLE) Method for the Design of High Efficiency Turbines, Compressors, and Isolated Airfoils

2011 ◽  
Author(s):  
T. Korakianitis ◽  
I. A. Hamakhan ◽  
M. A. Rezaienia ◽  
A. P. S. Wheeler
Keyword(s):  
Turbine Blade ◽  
High Efficiency ◽  
Turbine Blades ◽  
Circle Method ◽  
Three Dimensional ◽  
Leading Edge ◽  
Surface Curvature ◽  
Blade Design ◽  
Compressor Blades ◽  
Curvature Distribution

The prescribed surface curvature distribution blade design (CIRCLE) method is presented for the design of two-dimensional (2D) and three-dimensional (3D) blades for axial compressors and turbines, and isolated blades or airfoils. The original axial turbine blade design method is improved, allowing it to use any leading-edge (LE) and trailing-edge (TE) shapes, such as circles and ellipses. The method to connect these LE and TE shapes to the remaining blade surfaces with curvature and slope of curvature continuity everywhere along the streamwise blade length, while concurrently overcoming the “wiggle” problems of higher-order polynomials is presented. This allows smooth surface pressure distributions, and easy integration of the CIRCLE method in heuristic blade-optimization methods. The method is further extended to 2D and 3D compressor blades and isolated airfoil geometries providing smooth variation of key blade parameters such as inlet and outlet flow angles, stagger angle, throat diameter, LE and TE radii etc. from hub to tip. One sample 3D turbine blade geometry is presented. The efficacy of the method is examined by redesigning select blade geometries and numerically evaluating pressure-loss reduction at design and off-design conditions from the original blades: two typical 2D turbine blades; two typical 2D compressor blades; and one typical 2D isolated airfoil blade geometries are redesigned and evaluated with this method. Further extension of the method for centrifugal or mixed-flow impeller geometries is a coordinate transformation. It is concluded that the CIRCLE method is a robust tool for the design of high-efficiency turbomachinery blades.

scholarly journals On the prospects of improving the numerical analysis of symmetric airfoils at low Reynolds numbers and high angles of attack by a LES approach: the case of NACA0021 profile

2020 ◽  
Vol 197 ◽  
pp. 08015
Author(s):  
Simone Giaccherini ◽  
Filippo Mariotti ◽  
Lorenzo Pinelli ◽  
Michele Marconcini ◽  
Alessandro Bianchini
Keyword(s):  
Turbine Blades ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
High Fidelity ◽  
Complex Flow ◽  
Energy Applications ◽  
Low Reynolds ◽  
High Angles Of Attack

The working conditions of airfoils along modern wind turbine blades are putting new focus on the importance of properly characterizing the aerodynamic performance of different airfoil families also at high angles of attack (AoAs) beyond stall and at Reynolds numbers much lower (from few thousands to one million) than those commonly analyzed before. Several test cases are showing that even higher-order computational methods (like RANS/URANS CFD) are unable to properly capture the complex flow physics taking place past the blades, when deep stall occurs or when the AoA changes so rapidly to provoke the onset of dynamic stall. To fill this gap, the use of high-fidelity methods, like the Large Eddy Simulation (LES) is proposed, even though it implies a massive increase of the calculation cost. In order to analyze the prospects of using LES in comparison to RANS for low Reynolds, high AoAs, this work presents an in-depth study of the NACA 0021 aerodynamics at the Reynolds number of 80,000, by means of both traditional RANS approaches and high-fidelity (LES) simulations using the OpenFOAM suite. The selected airfoil has been showing in fact several issues in the correct characterization of its performance in similar conditions in many recent wind energy applications. The LES approach showed the ability to overcome the limitations of traditional RANS simulations, improving the accuracy of the results and reducing their dispersion thanks to the fact that the flow structures in the separated-flow regions are properly captured. Overall, this work underlines that accurate investigations of the aerodynamic performance of the NACA 0021 at low Reynolds require multiple sensitivity studies when RANS approaches are used, and suggests the use of LES simulations in order to increase the accuracy of estimations, especially when studying the stalledflow operating conditions of the airfoil.

Three-Dimensional Vortex Structure in a Leading-Edge Separation Bubble at Moderate Reynolds Numbers

1991 ◽  
Vol 113 (3) ◽  
pp. 405-410 ◽  
Author(s):  
Kyuro Sasaki ◽  
Masaru Kiya
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Plate Thickness ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Vortex Filaments ◽  
Separated Shear Layer ◽  
Hydrogen Bubbles ◽  
Edge Separation

This paper describes the results of a flow visualization study which concerns three-dimensional vortex structures in a leading-edge separation bubble formed along the sides of a blunt flat plate. Dye and hydrogen bubbles were used as tracers. Reynolds number (Re), based on the plate thickness, was varied from 80 to 800. For 80 < Re < 320, the separated shear layer remains laminar up to the reattachment line without significant spanwise distortion of vortex filaments. For 320 < Re < 380, a Λ-shaped deformation of vortex filaments appears shortly downstream of the reattachment and is arranged in-phase in the downstream direction. For Re > 380, hairpin-like structures are formed and arranged in a staggered manner. The longitudinal and spanwise distances of the vortex arrangement are presented as functions of the Reynolds number.

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