Dynamics of Protective Coatings to Limit Cavitation Damage

by Terry B. Armentrout, Dalles/John Day Dam, Dalles, United States,

Abstract: Cavitation implosions inflict a very high impact stress on turbine blades and turbine liners. One strategy for limiting the impact on the turbine components is to overlay a protective layer which will absorb the cavitation damage. Typically the overlay consists of 1/32 inch or 1/16 inch of polymer material, a thin adhesive material which bonds the polymer to the turbine steel, and of course the turbine steel. A cavitation induced shock wave propagates through the polymer material and either reflects or transmits into the steel. The relative acoustic impedances of the two materials determines whether the shock wave travels into the turbine steel or reflects back through the polymer. For the coating to be effective, the shock wave must either be reflected, attenuated or dispersed. This paper investigates the dynamic reactions at the polymer-steel boundary and evaluates the chances for success of this strategy.

Subject Headings: Turbines | Polymer | Cavitation | Steel | Shock waves | Wave reflection | Pavement overlays

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