Water Droplet Erosion Damage in a Steam Turbine Blade

Water droplet erosion (WDE) is "a form of materials wear that is caused by the impact of

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...

droplets with sufficiently high speed." The phenomenon was furthermore previously known as liquid impingement erosion (LIE).

Distinction from other phenomena

The emphasis of discrete

water droplet A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant ...

s serves to distinguish the WDE problem from liquid jet erosion and cavitation. The impact pressures invoked by discrete water droplet impact have a range considerably higher than the stagnation pressure created by liquid jet. The difference between WDE and

cavitation erosion Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...

is the fact that WDE usually comprises a

gas Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma). A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...

eous or

vapor In physics, a vapor (American English) or vapour (British English and Canadian English; American and British English spelling differences#-our, -or, see spelling differences) is a substance in the gas phase at a temperature lower than its critic ...

ous phase containing discrete liquid droplets; while cavitation erosion is observed when a continual liquid phase carries separate gaseous bubbles or cavities inside it. Recently, Ibrahim & Medraj developed an analytical model to predict the threshold speed of water droplet erosion and verified it experimentally, a challenge having been attempted hitherto without success since the 1950s.

Consequences

For an extended period of time, many industries have encountered the problem of erosion due to water droplet impact, and it continues to reappear wherever

rotation Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...

movement Movement may refer to: Common uses * Movement (clockwork), the internal mechanism of a timepiece * Motion, commonly referred to as movement Arts, entertainment, and media Literature * "Movement" (short story), a short story by Nancy Fu ...

of a component at high speed in a

hydrometer A hydrometer or lactometer is an instrument used for measuring density or relative density of liquids based on the concept of buoyancy. They are typically calibrated and graduated with one or more scales such as specific gravity. A hydrometer ...

environment is employed. Recently, with the use of larger wind

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

blades, the issue of erosion of the leading edge due to rain droplets has grown more grave.

Aerodynamic Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...

s efficiency of

turbine blades ...

is severely diminished due to leading-edge erosion, resulting in a considerable decrease in annual

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...

production.

References

Materials degradation {{Engineering-stub