scholarly journals Numerical Investigation of Turbine Blades with Leading-Edge Tubercles in Uniform Current

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2205
Author(s):  
Shuling Chen ◽  
Yan Liu ◽  
Changzhi Han ◽  
Shiqiang Yan ◽  
Zhichao Hong
Keyword(s):  
Flow Separation ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Hydrodynamic Performance ◽  
Micro Scale ◽  
Drag Forces ◽  
Uniform Current ◽  
Naca0018 Airfoil ◽  
Lift And Drag

Inspired by the tubercles on humpback whale flippers, leading-edge tubercles have been incorporated into the design of wings and turbine blades in an attempt to improve their hydrodynamic performance. Although promising improvements, especially in terms of the stall performance, have been demonstrated in the limited research that exists to date, the effectiveness of the leading-edge tubercles seems to be influenced by the base blade. This paper focuses on the introduction of sinusoidal leading-edge tubercles to a base blade developed from the classic NACA0018 airfoil, and numerically investigates the effectiveness of leading-edge tubercles on the hydrodynamics associated with the blade in uniform current with different attack angles. Both the macroscopic parameters, such as the lift and drag forces, and the micro-scale flow characteristics, including the vortex and flow separation, are analyzed. The results indicate that the leading-edge tubercles brings a significant influence on the hydrodynamic forces acting on the blade when subjected to an attack angle greater than 15°. This study also reveals the important role of the turbulence and flow separation on hydrodynamic loading on the blade and the considerable influence of the tubercles on such micro-scale flow characteristics. Although the conditions applied in this work are relatively ideal (e.g., the blade is fixed in a uniform flow and the end effect is ignored), the satisfactory agreement between the numerical and corresponding experimental data implies that the results are acceptable. This work builds a good reference for our future work on the hydrodynamic performance of tidal turbines which adopt this kind of blade for operating in both uniform and shearing currents.

Performance of S1210 Profile Used in Current Turbine Blades With Tubes Inserted at a Regular Interval

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Parikshit Kundu ◽  
Arunjyoti Sarkar ◽  
Vishwanath Nagarajan
Keyword(s):  
Flow Separation ◽  
Turbine Blades ◽  
Leading Edge ◽  
Suction Side ◽  
Current Speed ◽  
Separation Process ◽  
Hydrodynamic Performance ◽  
Drag Ratio ◽  
Lift To Drag Ratio ◽  
Current Turbine

Abstract The annual power output of a current turbine is affected by flow separation followed by the stall condition in an environment of varying current speed. Flow separation appears as the fluid in the boundary layer over the blade surface loses its kinetic energy. Delaying this separation process is essential to extract more power throughout the year considering the variation in the current speed. Several active and passive means are available in the literature today to achieve a delay in the flow separation process. Inserting tubes in an aero/hydrofoil at a constant spacing, connecting the fluid near the leading edge and a downstream location on the suction side is a novel approach that has been numerically investigated here. The baseline profile chosen here is S1210, which is used in the current turbine blades. The hydrodynamic performance of the profile with tubes has been compared with the baseline profile in terms of the force coefficients, lift to drag ratio, and stall angle. The maximum lift has been noticed to be increased by 18% and the stall is delayed by 2 deg (from 10 deg to 12 deg). The maximum lift to drag ratio is increased by 130% at 12 deg (beyond the stall of the baseline profile). The results show that the insertion of tubes can make the existing profile more efficient for the stated application.

A Review of Wind Turbine Polar Data and its Effect on Fatigue Loads Simulation Accuracy

2015 ◽  
Author(s):  
Matthew Lennie ◽  
Georgios Pechlivanoglou ◽  
David Marten ◽  
Christian Navid Nayeri ◽  
Oliver Paschereit
Keyword(s):  
Wind Turbine ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Leading Edge ◽  
Sensitivity Study ◽  
Wind Turbine Blades ◽  
Simulation Code ◽  
Simulation Accuracy ◽  
Inflow Turbulence ◽  
Lift And Drag

To certify a Wind Turbine the standard processes set out by the GL guidelines and the IEC61400 demand a large number of simulations in order to justify the safe operation of the machine in all reasonably probable scenarios. The result of this rather demanding process is that the simulations rely on lower fidelity methods such as the Blade Element Momentum (BEM) method. The BEM method relies on a number of simplified inputs including the coefficient of lift and drag polar data (usually referred to as polars). These polars are usually either measured experimentally, generated using tools such as XFoil or, in some cases obtained using 2D CFD. It is typical to then modify these polars in order to make them suitable for aeroelastic simulations. Some of these modifications include 360° angle of attack extrapolation methods and polar modifications to account for 3D effects. Many of these modifications can be perceived to be a black art due to the manual selection of coefficients. The polars can misrepresent reality for many reasons, for example, inflow turbulence can affect measurements obtained in wind tunnels. Furthermore, on real wind turbine blades leading edge erosion can reduce performance. Simulated polars can even vary significantly due to the choice of turbulence models. Stack these effects on top of the uncertainties caused by yaw error, pitch error and dynamic stall and one can clearly see an operating environment hostile to accurate simulations. Colloquial evidence suggests that experienced designers would account for all of these sources of errors methodically, however, this is not reflected by the certification process. A review of experimental data and literature was performed to identify some of the inaccuracies in wind turbine polars. Significant variations were found between a range of 2D polar techniques and wind tunnel measurements. A sensitivity study was conducted using the aeroelastic simulation code FAST (National Renewable Energy Laboratory) with lift and drag polars sourced using different methods. The results were post-processed to give comparisons the rotor blade fatigue damage; variations in accumulated damages reached levels of 164%. This variation is not disastrous but is certainly enough to motivate a new approach for certifying the aerodynamic performance of wind turbines. Such an approach would simply see the source of polar data and all post-processing steps documented and included in the checks performed by certification bodies.

scholarly journals Aerodynamic Analysis on Wind Turbine Aerofoil

2018 ◽  
Vol 7 (3.27) ◽  
pp. 456
Author(s):  
Albi . ◽  
M Dev Anand ◽  
G M. Joselin Herbert
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Cfd Simulation ◽  
Turbine Blades ◽  
Wind Turbine Blade ◽  
Wind Turbine Blades ◽  
Ansys Fluent ◽  
Wind Speeds ◽  
Drag Forces ◽  
Lift And Drag

The aerofoils of wind turbine blades have crucial influence on aerodynamic efficiency of wind turbine. There are numerous amounts of research being performed on aerofoils of wind turbines. Initially, I have done a brief literature survey on wind turbine aerofoil. This project involves the selection of a suitable aerofoil section for the proposed wind turbine blade. A comprehensive study of the aerofoil behaviour is implemented using 2D modelling. NACA 4412 aerofoil profile is considered for analysis of wind turbine blade. Geometry of this aerofoil is created using GAMBIT and CFD analysis is carried out using ANSYS FLUENT. Lift and Drag forces along with the angle of attack are the important parameters in a wind turbine system. These parameters decide the efficiency of the wind turbine. The lift force and drag force acting on aerofoil were determined with various angles of attacks ranging from 0° to 12° and wind speeds. The coefficient of lift and drag values are calculated for 1×105 Reynolds number. The pressure distributions as well as coefficient of lift to coefficient of drag ratio of this aerofoil were visualized. The CFD simulation results show close agreement with those of the experiments, thus suggesting a reliable alternative to experimental method in determining drag and lift.

Calculation of Optimal Surface Roughness With Respect to Lift/Drag Forces Acting on Wind Turbine Blade

2014 ◽  
Author(s):  
Xuerui Mao ◽  
Simon Hogg
Keyword(s):  
Surface Roughness ◽  
Boundary Conditions ◽  
Smooth Surface ◽  
Adjoint Equation ◽  
Turbine Blades ◽  
Leading Edge ◽  
Sensitivity Study ◽  
Small Magnitude ◽  
Viscous Forces ◽  
Drag Forces

Roughness on the surface of turbine blades induced by icing, dirt, erosion or manufacturing imperfections changes the aerodynamic configurations of wind turbines and reduces the power generation efficiency. In this work, a modified NACA0024 aerofoil is adopted to study effects of surface roughness on lift/drag forces. Three Reynolds numbers, 1000, 2000 and 5000 and a range of angles of attack [0°,20°] are studied. Since the magnitude of the roughness is small, it can be modelled as non-zero velocity boundary conditions imposed on the smooth surface without roughness. The flow with surface roughness can be therefore decomposed as the sum of a flow without roughness and a flow induced by roughness (or the velocity boundary conditions). The first flow can be obtained by solving the Navier-Stokes (NS) equation while the second one is governed by the linearized NS equation. Correspondingly the lift and drag forces acting on the aerofoil can be also decomposed as the sum of a force without considering roughness and a force induced by roughness. Instead of studying a particular type or distribution of roughness, we calculate the optimal roughness, which changes aerodynamic forces most effectively. This optimal roughness is obtained through a sensitivity study by solving an adjoint equation of the linearized NS equation. It is found that the optimal roughness with respect to both drag and lift forces is concentrated around the trailing edge and upper leading edge of the aerofoil and the lift is much more sensitive to roughness than the drag. Then the optimal roughness with a small magnitude is added to the smooth aerofoil geometry and this new geometry is tested through direct numerical simulations (DNS). It is found that the optimal roughness with a small magnitude (e-norm, defined as the square integration of the roughness around the surface, 0.001) induces over 10% change of the lift. Comparing the forces acting on the smooth surface and on the rough surface, it is noticed that the roughness changes the pressure force significantly while has little influence on the viscous forces. The pressure distribution is further inspected to study mechanisms of the effects of roughness on forces.

Analysis of the Flow Characteristics of Two Nonrotating Rotor Blades

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
R. P. J. O. M. van Rooij
Keyword(s):  
Aspect Ratio ◽  
Dominant Role ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Rotor Blades ◽  
Drag Coefficients ◽  
Wing Model ◽  
Stall Angle ◽  
Twisted Blade ◽  
Lift And Drag

The investigation focuses on the analysis of the airfoil segment performances along rotor blades in the parked configuration. In this research, wind tunnel experiments on two twisted blade geometries with different airfoils played a dominant role. These measurements were carried out by the Swedish Aeronautical Research Institute, former FFA, and by the American National Renewable Energy Laboratories (NREL) during the Unsteady Aerodynamic Experiment. The spans of the blades were 2.375m and 5m, the STORK 5 WPX and the NREL Phase VI blade, respectively. Five span locations (inboard, midspan, outboard, and tip regions) were considered and compared with the 2D airfoil characteristics. Wing model experiments with similar blade aspect ratio were included in the research. Furthermore, the commercial computational fluid dynamics code FLUENT was used for the validation and analysis of the spanwise lift and drag coefficients at four different pitch settings, 20deg, 30deg, 45deg, and 60deg. The computed pressure distributions compared reasonably well, but the derived lift and drag showed quite some differences with the blade measurements. The lift coefficients for the sections beyond the leading-edge stall angle of the STORK blade were larger than for the NREL blade and were close to that of a wing model with similar airfoil and aspect ratio. Lift and drag coefficients for the sections of the two blades were always much smaller than the 2D results. The drag values for both blades showed quite some agreement, and airfoil and blade dependency seemed to be small.

scholarly journals CFD Simulation of Flow Characteristics on Semi-Submersible Platforms

2020 ◽  
Vol 9 (1) ◽  
pp. 2777-2782
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Cfd Simulation ◽  
Transient Flow ◽  
Flow Characteristics ◽  
Slip Boundary Condition ◽  
Computational Domain ◽  
Hexahedral Mesh ◽  
Four Square ◽  
Lift And Drag

In this paper we present the turbulent flow around a semi-submersible platform, modelled using Ansys Fluent. The computational domain is designed as a rectangular horizontal channel with the semi-submersible platform mounted inside the channel. The top, bottom, left and right walls of the channel are treated with no slip boundary condition. The front and back walls are specified with velocity inlet and pressure outlet boundary conditions. The semi-submersible platform is designed with of two pontoons, four square columns and two bracings. The problem is modelled as three dimensional, transient, incompressible flow and turbulence is modelled using Large eddy simulation (LES) turbulence model. The computational domain is meshed to 4,72,749 hexahedral mesh cells. Parametric study is performed by varying the Reynolds number (Re) in the range of 104 ≤ Re ≤ 106 and also the shape of the columns. The investigation is carried out by plotting stream function, velocity and pressure contours. We observe vortex shedding and flow separation between the front and back columns of the semi-submersible platform. As we increase the Reynolds number the intensity of flow separation also increases. The transient flow characteristics of the lift and drag forces are evaluated by plotting the coefficients of lift and drag for different Reynolds number and column shapes

Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

2020 ◽  
pp. 095441002094690
Author(s):  
AA Mehraban ◽  
MH Djavareshkian ◽  
Y Sayegh ◽  
B Forouzi Feshalami ◽  
Y Azargoon ◽  
...  
Keyword(s):  
High Performance ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Drag Forces ◽  
Wide Range ◽  
Beam Bending ◽  
Low Reynolds ◽  
Lift And Drag ◽  
Drag Ratio

Sinusoidal leading-edge wings have shown a high performance after the stall region. In this study, the role of smart flaps in the aerodynamics of smooth and sinusoidal leading-edge wings at low Reynolds numbers of 29,000, 40,000 and 58,000 is investigated. Four wings with NACA 634-021 profile are firstly designed and then manufactured by a 3 D printer. Beam bending equation is used to determine the smart flap chord deflection. Next, wind tunnel tests are carried out to measure the lift and drag forces of proposed wings for a wide range of angles of attack, from zero to 36 degrees. Results show that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap. However, a combination of smooth leading-edge wing and smart flap advances the stall. Furthermore, it is found that wings with smart flap generally have a higher lift to drag ratio due to their excellent performance in producing lift.

Ground Effect on the Vortex Flow and Aerodynamics of a Slender Delta Wing

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
T. Lee ◽  
L. S. Ko
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Leading Edge ◽  
Ground Effect ◽  
Drag Forces ◽  
Wing Chord ◽  
Ground Distance ◽  
Lift And Drag ◽  
Wing Stall ◽  
Wing In Ground Effect

The ground effect on the aerodynamic loading and leading-edge vortex (LEV) flow generated by a slender delta wing was investigated experimentally. Both the lift and drag forces were found to increase with reducing ground distance (up to 50% of the wing chord). The lift increment was also found to be the greatest at low angles of attack α and decreased rapidly with increasing ground distance and α. The ground effect-caused earlier wing stall was also accompanied by a strengthened LEV with an increased rotational speed and size compared to the baseline wing. The smaller the ground distance, the stronger the LEV and the earlier vortex breakdown became. Meanwhile, the vortex trajectory was also found to be located further inboard and above the delta wing in ground effect compared to its baseline-wing counterpart. Finally, for wing-in-ground effect (WIG) craft with delta-wing planform the most effective in-ground-effect flight should be kept within 10% of the wing chord.

Numerical Investigation of Heat Transfer in Turbine Cascades With Separated Flows

2002 ◽  
Author(s):  
P. de la Calzada ◽  
A. Alonso
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Turbine Blades ◽  
Separated Flow ◽  
Leading Edge ◽  
Separated Flows ◽  
Separation Flow ◽  
Flow Angle ◽  
Starting Point ◽  
Transfer Mechanisms

Modern design of turbine blades usually requires highly loaded very thin profiles in order to save weight and cost. If local leading edge incidence is kept close to zero, then flow separation might occur on the pressure side. Although, it is known that flow separation, flow reattachment and the associated zones of re-circulation have a major impact on the heat transfer to the wall, the turbomachinery community needs an understanding of the heat transfer mechanisms in separated flows as well as models and correlations to predict it. The aim of the present investigation is a detailed study by means of an in-house CFD code, MU2 S2T, of the heat transfer mechanisms in separated flows, in particular in separation and reattachment point regions. Furthermore, an attempt is made to identify a limited number of parameters (i.e. Re, M, inlet flow angle, etc.) whose influence on the heat flux would be critical. The identification of these parameters would be the starting point to develop special correlations to estimate the heat transfer in separated flow regions.

Numerical Investigation of Heat Transfer in Turbine Cascades With Separated Flows

2003 ◽  
Vol 125 (2) ◽  
pp. 260-266 ◽  
Author(s):  
P. de la Calzada ◽  
A. Alonso
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Turbine Blades ◽  
Separated Flow ◽  
Leading Edge ◽  
Separated Flows ◽  
Separation Flow ◽  
Flow Angle ◽  
Starting Point ◽  
Transfer Mechanisms

Modern design of turbine blades usually requires highly loaded, very thin profiles in order to save weight and cost. If local leading edge incidence is kept close to zero, then flow separation might occur on the pressure side. Although it is known that flow separation, flow reattachment, and the associated zones of recirculation have a major impact on the heat transfer to the wall, the turbomachinery community needs an understanding of the heat transfer mechanisms in separated flows as well as models and correlations to predict them. The aim of the present investigation is a detailed study by means of an in-house CFD code, MU2S2T, of the heat transfer mechanisms in separated flows, in particular in separation and reattachment point regions. Furthermore, an attempt is made to identify a limited number of parameters (i.e., Re, M, inlet flow angle, etc.) whose influence on the heat flux would be critical. The identification of these parameters would be the starting point to develop special correlations to estimate the heat transfer in separated flow regions.

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