The impacts of the distribution of the airfoils of the blade on the performance of modern horizontal-axis wind turbines
This study targets the impact of the distribution of airfoils on the structural mechanics and aerodynamic performance of a rotor of a benchmark wind turbine at using the QBlade software, using global modeling with the BEM method and the
finite element method, by modifying the distribution of the blade profiles while retaining the initial dimensions, the resistance to stresses and the weight of the blades have been studied by varying the materials of manufacture of the blade. The results obtained are
compared with the reference model, an optimal distribution of profiles SG6043 / NACA 64618 has been found to be the most efficient in terms of power generation and with acceptable resistance to mechanical stress.
Part #1: Aerodynamic analysis
QBlade software overview
QBlade is a free software for the simulation and design of wind turbines using an XFOIL / XFLR5 functionality which is already integrated.This software is particularly suitable for teaching, as it provides practical design and simulation capabilities for HAWT and VAWT rotor design and shows all the fundamental relationships of design concepts and turbine performance in a way simple and intuitive.
QBlade also includes full post-processing functionality for rotor and turbine simulations and provides in-depth insight into all relevant blade and rotor variables. In addition to this, the resulting software is a very flexible and easy to use platform for designing wind turbine blades.
Remember : if you don t know how to use Qblade and you are looking for a short manual on how to use the software l may suggest you read this article
Type of airfoils that were chosen in this study
The six profiles when going to process in this study are (NACA64618, SD7062, S1091, S4022, S4320, and SG6043)
The polars CL (α) and Cd (α)
The curve of CL / Cd = f (α) makes it possible to deduce the optimal angle of attack corresponding to
(CL / Cd) max for each profile:
|a opt (°)||3.5||6||3.5||2.5||3||4|
The optimization of the blades
The optimization of the blades is the most important step to do it. We will complete a table in the HAWT Rotor Blade Design menu by the profile used with the position, the chord, the twist angle and the corresponding poles to this profile. In the same way we design the new blades: S1091, S4022, S4320, SD7062, SG6043, (S1091 + NACA64618), (S4320 + NACA64618), (SG6043 + NACA64618) and (SD7062 + NACA64618).
Power regulation by blade setting
Figure shows two power curves as a function of the wind speed, one for regulation by setting with a variable speed of rotation (omega) and the other for a constant speed of rotation the table below summarizes the results of the curve:
We can distinguish four parts on these curves:
• From 0 to starting speed: the output power is zero, the wind is not strong enough to cause the rotor to rotate
• From starting speed to nominal speed the output power increases until it reaches the nominal power.
• From nominal speed to cut-off speed, the output power is maintained at nominal power.
• After the cut-out speed: the wind turbine is shut down for protection, the output power is zero.
From the table, we also conclude that controlling the power of the turbine by varying the speed of rotation is advantageous on efficiency because the turbine can produce power from a speed lower than the starting speed for a turbine at a fixed speed.
|Vdémarrage (m/s)||Vnominale (m/s)||Vcoupure (m/s)||Pnominale (MW)|
|Ω =12.73 rpm||5||11.5||25||5.25|
|Ω [1rpm-12.73 rpm]||3||11.5||25||5.25|
So the results show that the stall regulation with a variable rotational speed () allows maximum power to be extracted at a lower starting speed.
QBlade is a software capable of determining the annual energy produced by a wind turbine from the parameters of the Weibull distribution which are entered into the software.
• The characteristics of the Turbine
|Start wind speed||3 m/s|
|Rated wind speed||12 m/s|
|Stopping wind speed||25 m/s|
|Specific wind speed||7|
|Rated rotational speed||12.73 rpm|
|Production Annuelle (GWh)|
|Turbine||Ω fixe||Ω variable|
|NRL 5 MW||18.560017||19.680258|
Through the results obtained, it is estimated by comparison that the annual production of electricity corresponding to the profile turbine (SG6043 + NACA 64618) is significant compared to the quantity of energy produced by the reference model (NRL 5 MW ) with a difference of 91,754 MWh.
These two results also show that the annual energy production for a variable rotational speed is greater than that for fixed Omega. In summary, the turbines which consist of blades where the variable distribution of the type of profiles (ex: SG6043 + NACA64618) are better than one which contains only one profile (ex: SD7062).
Part #2 : Dynamic analysis
The analysis of the dynamic behavior of the blades has an essential role in the design of wind turbines, because these blades are exposed during their operation to complex cyclic loads due to severe and highly variable environmental conditions such as the case of strong winds and gusts which generate extreme forces, thus promoting the deformation of the blades. Which is one of the serious issues that can hinder the proper functioning of wind turbines.
In this study, we relied on three wind turbine blades designed by: (SG6043 + NACA64618, S4022, SG6043), which are considered to be the best in aerodynamic terms and the most efficient compared to the benchmark turbine.
We will see in this study if these same three turbines have a high resistance to centrifugal and aerodynamic forces and stresses, and we will change the materials used in the manufacture of the blades and choose the appropriate material that must meet the objectives in order to obtain a structure which presents the highest performance / mass ratio.
Materials and structural calculation
We will try several materials for the internal and external structure of the blade, then we will finally choose among the materials available by the program the material that has good resistance and a lighter weight.
|Structure A||Structure B|
|Shell Material||1040 Carbon steel||1040 Carbon steel|
|Internal Material||1040 Carbon steel||20 GF 65D Polyuréthane|
|Type of internal structure||hollow with spar||hollow with spar|
Static blade loading (Deflection)
Discussion of results
This study has tried to combine all the results obtained in the aerodynamic and mechanical studies. This information indicates that the design of a high-performance wind turbine is more complex and depends on many parameters, which are classified as design criteria. These criteria can depend on the size of the wind turbine, the choice of materials, the distribution of profiles, and the aerodynamics of the blades.
Based on these results, the turbine designed by the SG6043 + NACA 64618 variant profile was chosen, being the most efficient in terms of optimum energy production and having acceptable stress resistance.