Robert Jasionowski

Optimization of Geometry of Cavitational Tunnel Using CFD Method

The liquid flow through a various kind of installation or devices is still not fully clarified issue. The liquid flow is assisted by a stream swirling, local pressure drops or changes of flow rates or temperature. CFD methods have been already implemented for few years to analyze phenomena related to the liquid flow. In this work Autodesk CFD Design Study Environment 2018 was used to simulate a new geometry of cavitational tunnel—a laboratory stand for examinations of cavitational resistance of structural materials. Three different geometries of the tunnel were analyzed in this work: with a cavitation initiator made of barricade and counter-barricade systems, with a cavitation initiator having a cylindrical pocket in counter-barricade and with a cavitation initiator having a double wedge shape. The introduced change of geometry allows multiplying the area of local pressure drop (i.e. the area of cavitation phenomenon). Obtained results of will serve in future (after building the new laboratory stand) to verify CFD simulations in a real testing conditions. The new tunnel geometry developed in CFD simulations should shorten evaluation time, what in turn, will give direct economic benefits (i.e. lower exploitation rate of the laboratory stand as well as lower costs of electrical energy).

The Evaluation of the Cavitational Damage in MgAl2Si Alloy Using Various Laboratory Stands

Evaluation of cavitation erosion resistance of is carried out by using various testing stands, that differ by the way of cavitation excitation and its intensity. These various testing conditions have led to a standardization of some part of laboratory stands, that in turn allows a direct comparison of results obtained in different laboratories. The aim of this study was to determine the course of cavitational destruction of MgAl2Si alloy samples tested on three different laboratory stands. The research was conducted on a vibration stand according to ASTM G32, where cavitation is forced by the vibrating element; in the cavitation tunnel reflecting actual flow conditions, and on a jet impact stand- simulating the impact microjet in the final phase of the cavitational bubbles implosion. Each laboratory stand has given a different course of cavitational destruction.

Cavitation Wear of CuZn10 Alloy in As-Cast State and after Plastic Working and Annealing

Copper alloys due to their very good corrosion properties are often used to a fabrication of components that are subjected to both a cavitational destruction and a corrosive action of an environment, e.g.. ships’ propellers, sliding elements, pump parts etc. The course of cavitational destruction depends mainly on a material’s structure (a grain size, a type of inclusions, morphology and phase distribution, etc.) but also on the load distribution, and a possible activity of chemical, electrochemical and thermal processes near cavitation bubbles. Properties of a material that is subjected to the cavitational damage are strongly affected by its structure formed upon manufacturing or applied processing. In the present paper, results of the cavitational resistance analysis of CuZn10 alloy in the as cast state (the grain size of 200 μm) and after thermomechanical processing (the grain size of 10 or 200 μm) evaluated on vibrational laboratory stand in accordance with ASTM G-32 standard, are shown.

The Destruction Mechanism of Titanium Subjected to Cavitation Erosion

A cavitation erosion is the process based on an impact of pressure pulses on a material’s surface caused by the phenomenon of cavitation. The term cavitation is defined as a phenomenon of formation, growth and disappearance (implosion) of bubbles due to cyclic pressure variations in a liquid. The cavitation initiators are embryos (cavitation nuclei with a size up to 50 μm), located in the water or on wetted surfaces that lead to decreasing of the liquid ability to transfer tensile stresses. The role of embryos is played by micro gas bubbles, fine solid particles, micro-organisms or gas-filled pores on a surface of solid body embedded in a liquid. A rapid pressure drop occurring within the liquid and a presence of cavitational kernel causes rupture the continuity of the liquid and thus lead to the formation of steam-gas mixture areas, a so called cavitation bubbles. A cavitation bubble may be filled with a gas, a vapor or a steam/gas mixture.A course of cavitation depends on a cavitation type. In thepresent work, a mechanism of cavitiational destruction of 99,7 % titaniumtested on vibrational and jet-impact valaboratory stands, is analyzed. Results of thecavitational resistance evaluation of Ti99.7 titanium carried out onvibrational and jet-impact stands have revealed different mechanisms of acavitation destruction caused by various forms of cavitation. It was found thata surface of titanium samples tested on the vibratory stand was covered by verylarge number of microcracks which in a later stage of the research leads to theerosion of the material. The cavitational destruction of Ti samples on the jet-impact stand is initiatedby a plastic straining of subsurface area, which in the further stage leads toan erosion represented by the detachment of whole grains anda formation of deep pits on the material’s surface. Additionally, results of conducted studies have confirmed the fatigue character of the cavitationaldestruction process.

Analysis of the Effect of the Wearing Type on Surface Structural Changes of Ni3Al-Based Intermetallic Alloy

Results of an analysis of effect of wearing type on surface structural changes of a Ni3Al intermetallic alloy, are shown in the present paper. A microstructure evaluation was carried out by Quanta 3D FEG field emission gun scanning electron microscope (FEG SEM) equipped with an integrated EDS/WDS/EBSD system. The Ni3Al-based intermetallic alloy with an addition of boron, zirconium and chromium was examined. The investigated material had γ’ single-phase, ordered solid solution structure with 20 μm grain size. An electron backscatter diffraction (EBSD) method was applied to visualize surface structural changes upon an abrasive, a cavitational and a tribological wearing of the material.An observation of surface layer after the abrasive wear was carried out on samples examined in loose abradant by T-07 tester and according to GOST 23.2008-79 norm. An analysis of cavitational wear on changes in the near surface area of Ni3Al-based alloy was performed on an impact-jet stand. Observed structural changes were described based on results of the SEM/EBSD complex structural examination and hardness measurements. It was found, that the EBSD is an effective and sensitive method that allows estimating surface strain introduced during analyzed wearing types.

Cavitation Erosion and Corrosion of Pearlitic Gray Cast Iron in Non-Standardized Cavitation Conditions

A results of test of erosion and corrosion resistance of pearlitic gray cast iron (grade EN GJ 400) are showed. The NaCl solutions and of ethylene glycol solutions were used as the test environment. Examination were performed at varying cavitation load, in the range 2,8 ÷ 20 W/cm2.

The Effect of Aluminum Content on the Microstructure and Cavitation Wear of Feal Intermetallic Alloys

Abstract Intermetallic-based alloys (so called intermetallics) of the Fe-Al binary system are modern construction materials, which in recent decades have found application in many branches of the power, chemical and automotive industries. High resistance of FeAl based alloys to cavitational erosion results first of all from their high hardness in the as-cast state, large compressive stresses in the material, as well as homogeneous structure. In the present paper, the effect of aluminum content on the microstructure, texture and strain implemented upon cavitation wear of FeAl intermetallic alloys, have been analyzed by field emission gun scanning electron microscopy (FEG SEM) and electron backscatter diffraction (EBSD) analysis. Obtained results of structural characterization indicates that with increasing aluminium content effects of orientation randomization (weakening of <100>//ND casting texture), grain refinement and rising of mechanical strenght (and so cavitational resistance) take place.