Research On Investigation Of Pressure Force Effect On A Wind Turbine Performance Using BEM

Air as a matter once set into motion will possess impetus developing a net force aroundcurved surfaces and transform the kinetic energy of the wind to mechanical energy through aconnecting shaft to produce electricity in the generator. Aerodynamics is used as a mainmodeling tool in the concept designs of turbines with the help of blade element momentumtheory to understand the fundamentals of wind turbine aerodynamics.A one dimensional classical momentum theory has been at the center of aerodynamicmodeling presuming uniform axial induction factor that gives an ideal maximum power. Thismodel ignores the role of pressure force on the performance of wind turbines. However,recent studies indicate the presence of certain effect on performance of wind turbines. Thepresent master’s thesis investigates effect of pressure force on wind turbine performance.The current thesis will introduce the basics of Froude’s actuator disc momentum andGlauert’s blade element theories separately; later synergy of the two theories is presented tocomplete the information required for aerodynamic modeling based on BEM theory. For thefact that turbine blades work for pre-stall and post-stall conditions, the concept of separationand the implicit role of rotation on stall-delay is explained to assist in modeling the actualrotor blade operation. To make the necessary modification to the existing momentum theory,initially, a blade analysis result from national renewable energy laboratory combinedexperimental rotor, NREL CER, report is used as a basis to write a code. Based on thisreport‘s result an in-house code is written to simulate flow around a stream tube surroundinga S809airfoil using the method of blade element momentum theory. Once the Matlab basedcode is verified against the report by NREL, modification that includes the role of pressureforce is included in the classical blade element momentum model. Based on the new model,performance prediction parameters including post-stall operations are studied for threedominant variable blade geometry parameters. Three case studies carried out for fourdifferent wind speeds representing both pre-stall and post-stall turbine operations. Thecoefficients of lift and drag, inflow factors, rotor power, and thrust forces on the blade areselected to serve as performance prediction parameters. These parameters are computed for acombination of different wind speeds and angles of attack. After applying axial component of pressure force, corresponding curves are compared against the graphs for classical blademodel. Finally, a simple and unsophisticated analysis is carried out in order to evaluate theimpact, and future consideration of axial component pressure force on a wind turbine blademodels.The simulation result proves the presence of wind performance reduction as a result ofpressure force consideration. This reduction in performance shows overestimation of turbinepower out puts in the current design practices. In future models shall consider this forcecomponent in order to have a fairly accurate annual energy estimate from turbines. However,the current research work has drawbacks with regards to accurate modeling of the fully–stallregion operation. In addition the sensitivity of wind tunnel aerodynamic coefficients leads tosome expected deviation in predicted values even in the pre-stall condition. Moreover, theinability of BEM theory to account for vorticity at the tip of blade, high contributor of liftforces, makes the result acceptably inaccurate. However, relative error is most important thanabsolute errors that serves to evaluate the deviation in performance prediction. With this ideain mind future work on this topic shall emphasis on the collection of accurate data, andimplementation of a fairly accurate post-stall model that could predict the actual situation.Beside, this work needs to be experimentally verified to get a full picture on the existingproblem.