Abstract
The issue of leading edge erosion (LEE) of wind turbine blades (WTBs) is a complex problem that reduces the aerodynamic efficiency of blades, and affects the overall cost of energy. Several research efforts are being made at the moment to counter erosion of WTBs such as-testing of advanced coating materials together with development of high-fidelity computational models. However, the majority of these studies assume the coated surfaces as flat, while the surface curvature and the shape of the aerofoil at the blade’s leading-edge exposed to such rain fields is neglected. The present study questions the assumption of a flat surface, in the context of LEE of WTBs, and provides guidelines for erosion modelling. The critical parameters associated with rain droplet impingement kinematics on leading edge are compared for blade impact with (a) flat surface assumptions together with (b) the effects of the blade’s surface curvature. A parametric study is performed which includes WTBs of varying sizes and power ratings ranging from 750 KW to 10 MW, different positions along the blade length, and different rain droplet radii ranging from 0.1 mm to 5 mm for a land based wind turbine operating at rated wind speed. It is found in the study that droplet impingement kinematics are influenced by the surface curvature at the leading edge, the effect of which is significant for representing erosion at the blade tip for smaller blades, and for exposure to rainfall intensity with larger rain droplet size. A master curve describing the threshold level along the blade length is established for various WTBs and rainfall conditions, where flat surface approximation of the surface yields noticeable error and violates the impingement process. The results of the study are expected to aid the modeller in developing advanced numerical models for LEE for WTBs.
Highlights
The constant demand for renewable sources of energy has led to rapid growth of large size wind turbines both in onshore and offshore sector[1]
It is found in the study that droplet impingement kinematics are influenced by the surface curvature at the leading edge, the effect of which is significant for representing erosion at the blade tip for smaller blades, and for exposure to rainfall intensity with larger rain droplet size
A master curve describing the threshold level along the blade length is established for various wind turbine blades (WTBs) and rainfall conditions, where flat surface approximation of the surface yields noticeable error and violates the impingement process
Summary
The constant demand for renewable sources of energy has led to rapid growth of large size wind turbines both in onshore and offshore sector[1]. One of the issues related to WTBs is their leading edge erosion (LEE) which is due to the effects of harsh environmental conditions during their service life, such as repeated rain droplet impact during heavy precipitation (Fig. 1(a)). Such damages have adverse influences on their aerodynamic performance, primarily due to roughening of surfaces. Emphasis is placed on computational modelling of erosion [12, 13, 14] for understanding rain droplet impingement kinematics, kinetics as well as model damages in the blade due to rain droplet impact Such models are expected to contribute towards enabling efficient analysis and design of coating materials for WTBs, as an alternative to costly experiments.
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