Abstract
In turbomachinery, their blade leading edges are critical to performance and therefore fuel efficiency, emission, noise, running and maintenance costs. Leading edge damage and therefore roughness is either caused by subtractive processes such as foreign object damage (bird strikes and debris ingestion) and erosion (hail, rain droplets, sand particles, dust, volcanic ash and cavitation) and additive processes such as filming (from dirt, icing, fouling, insect build-up). Therefore, this review focuses on the changes in topography induced by during service to blade leading edges and the effect of roughness and form on performance and efforts to predict and model these changes. The applications considered are focused on wind, gas and tidal turbines and turbofan engines. Repair and protection strategies for leading edges of blades are also reviewed. The review shows additive processes are typically worse than subtractive processes, as the roughness or even form change is significant with icing and biofouling. Antagonism is reported between additive and subtractive roughness processes. There are gaps in the current understanding of the additive and subtractive processes that influence roughness and their interaction. Recent work paves the way forward where modelling and machine learning is used to predict coated wind turbine blade leading edge delamination and the effects this has on aerodynamic performance and what changes in blade angle would best capture the available wind energy with such damaged blades. To do this generically there is a need for better understanding of the environment that the blades see and the variation along their length, the material or coated material response to additive and/or subtractive mechanisms and thus the roughness/form evolution over time. This is turn would allow better understanding of the effects these changes have on aerodynamic/ hydrodynamic efficiency and the population of stress raisers and distribution of residual stresses that result. These in turn influence fatigue strength and remaining useful life of the blade leading edge as well as inform maintenance/repair needs.
Highlights
In open and enclose turbomachinery, the shape and roughness of the leading edge of the blades is critical to their performance, which includes fuel efficiency, emissions, noise, and operating and maintenance costs
There is a growing library of research papers dedicated to roughness and form effects of blade leading edges in turbomachinery, see Figure 33
This review found over 180 papers mainly in the past 20 years
Summary
In open and enclose turbomachinery (both axial and radial machines), the shape and roughness of the leading edge of the blades is critical to their performance, which includes fuel efficiency, emissions, noise, and operating and maintenance costs. Based on the combined effect of the different degrees in efficiency loss across the engine cycle, a 1% increase in fuel burn was seen due to erosion of the leading edges [3]. Such solutions involve functionally graded surfaces or coatings to protect the leading edge Other technologies such as flow control methods, either passive [6] or active [7], are being investigated to improve the aerodynamic performance of wind turbine aerofoils that suffer increased surface roughness. Considerable research is focused on leading edge protuberances, as a passive control method to improve the performance of hydrodynamic or aerodynamic bodies, such as aerofoils, wind turbine blades, propellers, rudders, and hydrofoils [16]. This paper has not included roughness / texturing effects of other parts of the blade
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