CFD에 의한 블레이드 팁 전연 부 마모현상이 풍력터빈 출력성능에 미치는 상관관계 분석

Abstract

With the accelerating development of the wind power technology and the growth of the offshore wind power market, the rotor size and the tower height are continuously increasing. Even though the increase of the swept area has increased the power generation of the wind turbine, the relative speed of the blade tip has also increased, resulting in more frequent blade damages due to the external environment. Since the surface of airfoils at the blade tip with a high aerodynamic efficiency has a particularly high susceptibility, it can cause large losses in annual energy production when the wind turbine is operated for a long time. With respect to this issue, many researchers have recently studied the relationship between damage to the blade leading edge and the annual energy production. The ideal method to determine the cause of decreasing blade efficiency and performance is through experiments using actual physical phenomena, but it is not easy because it requires considerable cost and time. Hence, many studies have attempted numerical analysis using CFD (Computational Fluid Dynamic) codes. The reliability of the numerical analysis modeling technique has improved to the level of experimental data when a turbulence model based on the Reynolds-Averaged Navier-Stokes (RANS) equation was applied. However, most of the existing studies mostly use two-dimensional analysis for the airfoil section, and as a result, overestimate the flow separation point because they do not consider three-dimensional flow phenomenon. In order to evaluate the aerodynamic performance at the highly susceptible tip of the leading edge, the physical phenomenon should be more accurately simulated using three-dimensional analysis. This study proposes a numerical modeling method using CFD for the flow and performance change characteristics according to the wear condition of the blade leading edge. The leading edge wear condition was defined and the aerodynamic data of the NACA64_618 airfoil were obtained through CFD simulation. The airfoil aerodynamic analysis results were compared with the results of a wind tunnel test conducted by I. H. Abbott at the Reynolds number 6.0E+06. Based on these results, a numerical analysis method and a turbulence model suitable for 3D wind turbine analysis were established. For the comparison with the 3D wind turbine analysis results, the power generation of a wind turbine was calculated by applying the data obtained through the airfoil simulation to the BEMT (Blade Element Momentum Theory). The calculated power generation was compared with the result of a 3D wind turbine analysis conducted under the final unsteady state analysis condition. The calculation of wind turbine performance using the BEMT has the problem of incompleteness, such as the assumption of independence between blade elements. This problem occurs largely when the effect of the three-dimensional flow is not considered, which results in a higher performance than expected. When the results of the BEMT were compared with those of the unsteady state 3D wind turbine analysis in this study, the power generation in the results of the unsteady state 3D wind turbine analysis was lower by 6.5%. However, the performance reduction rate due to wear was approximately 3% in the results of both the BEMT and the unsteady state 3D wind turbine analysis. In conclusion, even though the BEMT has a tendency to overestimate the performance because it depends on the aerodynamic data of the two-dimensional airfoil, the two results show relatively good agreement.