I want to know if there is any formula to calculate the clearance between tip of blade and tower so when the blade deflects it won't touch the tower.
my answer will be limited to small HAWTS
Blade flexing is less critical in small HAWTS as small blades tend to be mounted further from the tower as a fraction of blade radius. Nevertheless,according to IEC61400–2 requirement, that (stationary) blade deflection under the extreme wind load is less than the distance from the blades to the tower divided by the appropriate ‘partial load factor’, either 1.35 or 3.0, is often a considerable challenge in the absence of centrifugal stiffening by rotation.
A wind turbine blade is basically a cantilever beam. Therefore, you could simply model it as a multi-segment beam where each element as equivalent bending stiffness to the corresponding actual region and with a distributed loads.
You should have a look at computer codes maintained by the NREL like AERODyn, YawDyn and FAST wich are aero and aeroelastic solver for horizontal axis wind turbines. I'm not personally proficient with them but I know they could make the calculations for you provided you can feed them the right inputs.
Best regards,
Laurent is right, you can use FAST and AeroDyn. They are well-known, well-accepted codes, applied successfully in many previous investigations. Also, FAST and AeroDyn are freeware (open access software), and it is possible to periodically download improvements of these tools. You can also use QBlade, which I explain in the last paragraph.
These coupled software tools were developed by the National Renewable Energy Laboratory (NREL) for aeroelastic simulation of horizontal-axis wind turbines (HAWT): FAST is a dynamics analysis code, and AeroDyn is an aerodynamics analysis routine capable of interfacing with FAST. In particular, the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code “is a comprehensive aeroelastic simulator capable of predicting both the extreme and fatigue loads of two- and three-bladed HAWT”. AeroDyn is an element-level wind-turbine aerodynamics analysis routine that, when used in conjunction with dynamics software (e.g., FAST, YawDyn or SymDyn wind turbine dynamics analysis codes, or ADAMS® commercial dynamics analysis package), allows computing the aerodynamic loads on the blade elements of HAWT. For this purpose, AeroDyn uses essentially two wake models: the blade element momentum (BEM) theory, and the generalized dynamic-wake theory, a model for skewed and unsteady wake dynamics. Both models are used basically to calculate the axial induced velocities from the wake in the rotor plane, taking into account the influence of tip losses, hub losses and skewed wakes. AeroDyn uses also a dynamic stall model based on the semi-empirical Beddoes-Leishman model, and a tower shadow model based on potential flow around a cylinder and an expanding wake. Since FAST and AeroDyn incorporate models of controller (servo) dynamics and structural (elastic) dynamics, they enable also simulation of the behavior of the control and protection systems and the structural dynamics. It is worth to note that FAST and ADAMS®, together with AeroDyn, were evaluated in 2005 by Germanischer Lloyd WindEnergie and found adequate for computation of loading of onshore wind turbines for design and certification.
These tools require several input files containing diverse data like, for example, the wind-inflow conditions, and physical and aerodynamics parameters of the wind turbine blades. The first step is thus to characterize the wind turbine selected for your study and to build the input files requested by FAST and AeroDyn. You can do that using the information and technical data provided by the manufacturers, and data measured from the physical components.
QBlade is open source software for design and simulation of HAWT, distributed under the GNU General Public License. Its integration in XFOIL allows airfoil design and airfoil performance analysis. QBlade allows also for extrapolation of airfoil performance data to 360° angle of attack, turbine blade design, and realization of BEM simulations of the rotor and turbine. Finally, this tool allows structural blade design, modal and static loading analyses using QFem solver, generation of turbulent windfields, and realization of FAST simulations. You can download it here:
http://qblade.npage.de/
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