scholarly journals CAVITATION EROSION MECHANISM: NUMERICAL STUDY OF THE INTERACTION BETWEEN PRESSURE WAVES AND VAPOR BUBBLES

2021 ◽  
Vol 774 (1) ◽  
pp. 012024
Author(s):  
C. Leclercq ◽  
R. Fortes-Patella ◽  
A. Archer
Keyword(s):  
Cavitation Erosion ◽  
Numerical Study ◽  
Pressure Waves ◽  
Vapor Bubbles ◽  
Erosion Mechanism

Numerical Study of the Effect of Inlet Constriction on Bubble Growth During Flow Boiling in Microchannels

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Stokes Equations ◽  
Numerical Study ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Vapor Bubbles ◽  
Reversed Flow ◽  
Cross Sectional ◽  
Parallel Microchannels ◽  
Energy Equations

Flow boiling through microchannels is characterized by nucleation of vapor bubbles on the channel walls and their rapid growth as they fill the entire channel cross-section. In parallel microchannels connected through a common header, formation of vapor bubbles often results in flow maldistribution that leads to reversed flow in certain channels. The reversed flow is detrimental to the heat transfer and leads to early CHF condition. One way of eliminating the reversed flow is to incorporate flow restrictions at the channel inlet. In the present numerical study, a nucleating vapor bubble placed near the restricted end of a microchannel is numerically simulated. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid-vapor interface is captured using the level set technique. The results show that with no restriction the bubble moves towards the nearest channel outlet, whereas in the presence of a restriction, the bubble moves towards the distant but unrestricted end. It is proposed that channels with increasing cross-sectional area may be used to promote unidirectional growth of the vapor plugs and prevent reversed flow.

Numerical Study of Erosion Mechanism due to Online Water Washing in Axial Flow Compressors

2021 ◽  
Author(s):  
Paolo Venturini ◽  
Francesca Di Gruttula ◽  
Giuliano Agati ◽  
Serena Gabriele ◽  
Domenico Simone ◽  
...  
Keyword(s):  
Numerical Study ◽  
Axial Flow ◽  
Erosion Mechanism ◽  
Water Washing ◽  
Axial Flow Compressors

Cavitation Erosion of HVOF Coatings

1996 ◽  
Author(s):  
R. Schwetzke ◽  
H. Kreye
Keyword(s):  
Erosion Rate ◽  
Cavitation Erosion ◽  
Metallic Alloys ◽  
Erosion Mechanism ◽  
Hvof Coatings ◽  
Coating Composition ◽  
Before And After ◽  
Series Of Experiments ◽  
The Individual ◽  
Scanning Electron

Abstract The proposed paper reports a series of experiments to investigate the cavitation erosion mechanism of HVOF coatings. Vibratory cavitation erosion tests according to ASTM G 32 have been carried out with several HVOF coatings including cermets, oxides and metallic alloys. The steady state erosion rate for each coating was determined and the effect of coating composition and microstructure on the erosion rate was investigated. The morphology and microstructure of the various coatings before and after cavitation testing were analyzed by means of light optical and scanning electron microscopy in order to study the erosion mechanism. The results demonstrate that HVOF coatings of NiCrFeBSi, WC-17Co, Cr3C2-25NiCr and Cr2O3 can exhibit a rather high resistance against cavitation erosion and should be considered for application as a protective surface layer against cavitation. Furthermore, it is shown that cavitation testing can provide a useful tool to study and characterize the bond strength between individual splats as well as the brittleness of the individual phases present in the coating.

scholarly journals Numerical Study of Sediment Erosion Analysis in Francis Turbine

2019 ◽  
Vol 11 (5) ◽  
pp. 1423 ◽  
Author(s):  
Md Rakibuzzaman ◽  
Hyoung-Ho Kim ◽  
Kyungwuk Kim ◽  
Sang-Ho Suh ◽  
Kyung Kim
Keyword(s):  
Erosion Rate ◽  
Cavitation Erosion ◽  
Numerical Study ◽  
Leading Edge ◽  
Suction Side ◽  
Hydraulic Turbine ◽  
Francis Turbine ◽  
Trailing Edge ◽  
Sand Erosion ◽  
Turbine Design

Effective hydraulic turbine design prevents sediment and cavitation erosion from impacting the performance and reliability of the machine. Using computational fluid dynamics (CFD) techniques, this study investigated the performance characteristics of sediment and cavitation erosion on a hydraulic Francis turbine by ANSYS-CFX software. For the erosion rate calculation, the particle trajectory Tabakoff–Grant erosion model was used. To predict the cavitation characteristics, the study’s source term for interphase mass transfer was the Rayleigh–Plesset cavitation model. The experimental data acquired by this study were used to validate the existing evaluations of the Francis turbine. Hydraulic results revealed that the maximum difference was only 0.958% compared with the CFD data, and 0.547% compared with the experiment (Korea Institute of Machinery and Materials (KIMM)). The turbine blade region was affected by the erosion rate at the trailing edge because of their high velocity. Furthermore, in the cavitation–erosion simulation, it was observed that abrasion propagation began from the pressure side of the leading edge and continued along to the trailing edge of the runner. Additionally, as sediment flow rates grew within the area of the attached cavitation, they increased from the trailing edge at the suction side, and efficiency was reduced. Cavitation–sand erosion results then revealed a higher erosion rate than of those of the sand erosion condition.

Numerical Method for Studying Bearing Gap Pressure Wave Development and Subsequent Performance Mapping of Externally Pressurized Gas Journal Bearings

2019 ◽  
Author(s):  
Tom M. Lawrence ◽  
Marvin D. Kemple
Keyword(s):  
Numerical Method ◽  
Cross Section ◽  
Mass Flow ◽  
Pressure Wave ◽  
Design Space ◽  
Numerical Study ◽  
Pressure Waves ◽  
Wide Range ◽  
Wave Development ◽  
Static Instability

Abstract In previous work, numerical methods were developed to determine the pressure waves (pressure distribution) in the bearing gap of round externally pressurized gas bearings (EPB’s) that were pressurized through porous liners (PL bearings) or through liners with rows of feedholes (FH bearings). When integrated and differentiated these pressure portraits yield the net hydrodynamic force (FH) between the shaft and the bushing and the mass flow rates through the bearing gap. These results successfully replicated force-deflection curves and mass flow rate data for experimentally tested prototype FH and PL bearings over a wide range of mass flow constriction and clearances. Subsequently the numerical study was expanded to a broader design space of clearance and mass flow compensation. Also, a bearing performance mapping method of mapping the normalized bearing load over the clearance-eccentric deflection plane was developed for different levels of mass compensation. These performance maps produced a very interesting result as they indicated certain areas in the design space of FH bearings where static instability (negative stiffness) would be encountered. This static instability was not observed in the experimental data but is noted in references as known to occur in practice. Because this numerical method is based on the development of pressure wave portraits, the FH pressure wave could then be “dissected” in the areas of the onset of static instability which gave much insight as to the possible causes of static instability. This initial work, then, was perhaps the first to predict where in design space static instability would occur and yield some insight via examination of the corresponding pressure waves as to the cause. The numeric techniques developed, however are in no way limited to non-rotating bearings but are extensible to rotating bearings. The method is also easily extensible to examination of any configuration of feedholes or orifices. Nor is it limited to parallel deflections but can yield results for unbalanced loads. The method is also not limited to round bearings but can be applied to any cross-section configuration of bearing gap cross section such as a 3 lobed bearing or a slotted 3 lobed bearing. Examination of the resulting pressure wave development patterns for different scenarios can be examined to garner insight as to the causes of differing performance that can be applied to alterations towards optimization. Thus sharing in detail the developed numerical method underlying these studies seems worthwhile.

scholarly journals Mitigating cavitation erosion using biomimetic gas-entrapping microtextured surfaces (GEMS)

2020 ◽  
Vol 6 (13) ◽  
pp. eaax6192 ◽  
Author(s):  
Silvestre Roberto Gonzalez-Avila ◽  
Dang Minh Nguyen ◽  
Sankara Arunachalam ◽  
Eddy M. Domingues ◽  
Himanshu Mishra ◽  
...  
Keyword(s):  
Solid Surface ◽  
Surface Hardening ◽  
High Speed ◽  
Cavitation Erosion ◽  
Flow Problem ◽  
Vapor Bubbles ◽  
Cavitation Damage ◽  
Cavitation Bubbles ◽  
Microtextured Surfaces ◽  
High Speed Flows

Cavitation refers to the formation and collapse of vapor bubbles near solid boundaries in high-speed flows, such as ship propellers and pumps. During this process, cavitation bubbles focus fluid energy on the solid surface by forming high-speed jets, leading to damage and downtime of machinery. In response, numerous surface treatments to counteract this effect have been explored, including perfluorinated coatings and surface hardening, but they all succumb to cavitation erosion eventually. Here, we report on biomimetic gas-entrapping microtextured surfaces (GEMS) that robustly entrap air when immersed in water regardless of the wetting nature of the substrate. Crucially, the entrapment of air inside the cavities repels cavitation bubbles away from the surface, thereby preventing cavitation damage. We provide mechanistic insights by treating the system as a potential flow problem of a multi-bubble system. Our findings present a possible avenue for mitigating cavitation erosion through the application of inexpensive and environmentally friendly materials.

Cavitation erosion mechanism of NiTi coatings made by laser plasma hybrid spraying

Wear ◽  
1999 ◽  
Vol 231 (2) ◽  
pp. 272-278 ◽  
Author(s):  
Hitoshi Hiraga ◽  
Takashi Inoue ◽  
Hirofumi Shimura ◽  
Akira Matsunawa
Keyword(s):  
Laser Plasma ◽  
Cavitation Erosion ◽  
Erosion Mechanism

scholarly journals Study of the working process of a diesel engine with modified fuel

2021 ◽  
Vol 2131 (2) ◽  
pp. 022073
Author(s):  
G Yur ◽  
E Nosonova
Keyword(s):  
Diesel Engine ◽  
Fuel Consumption ◽  
Numerical Study ◽  
Gas Temperature ◽  
Vapor Bubbles ◽  
Fuel Gas ◽  
Operation Process ◽  
Study Results ◽  
Exhaust Fumes ◽  
Exhaust Gas Temperature

Abstract The research objective is to reduce specific fuel consumption and emissions of exhaust fume pollutants. Specifically treated (modified) fuel is used to comprehensively improve the economic and environmental performance of the diesel operation process. Fuel treatment was carried out at a pilot plant using the process of fuel gas cavitation. During processing, high-molecular fuel compounds were broken down and the fuel was saturated with gas-vapor bubbles. The description of the pilot unit is given. The characteristics of the base distillate and modified fuel are studied. A mathematical model and the numerical study results of the fuel droplet development containing vapor-gas bubbles are presented. An experimental study of the work process in a 10.5/12 H diesel engine single-cylinder compartment when operating on various fuels was carried out. Diesel tests have shown that when using modified fuel, the specific indicative fuel consumption has decreased by 5-7 per g / kWh, the exhaust gas temperature has decreased by 5-8 degrees, the concentration of nitrogen oxides in the exhaust fumes has decreased by 32-46 ppm, the concentration of total hydrocarbons has decreased by 9-14 ppm, the smoke content has decreased by 1.2-1.7 times.

Optimization of Testing Method in Comparison with the Coated Composites and Metals by Vibratory Cavitation Test

2004 ◽  
Vol 261-263 ◽  
pp. 1397-1402
Author(s):  
Yun Hae Kim ◽  
Y.J. Son ◽  
B.H. Woo ◽  
C.W. Bae ◽  
S.M. Kim ◽  
...  
Keyword(s):  
Cavitation Erosion ◽  
Sea Water ◽  
Digital Camera ◽  
Test Methods ◽  
Vapor Bubbles ◽  
Cavitation Damage ◽  
Piezoelectric Vibrator ◽  
Testing Method ◽  
Fluid Handling ◽  
Hydrodynamic Phenomenon

Cavitation-erosion is a hydrodynamic phenomenon that results in the formation and collapse of vapor bubbles in a liquid. Cavitation damage is encountered in a wide variety of fluid handling machinery and over a broad range of liquid pressures and temperatures. In this study, cavitation damage was investigated by using the piezoelectric vibrator with 20kHz, 50μm to cavity generation apparatus. At the first cavitation test, coated composite material specimens appear to generating the low bubbles due to damping vibration. This study is mainly compared with cavitation test (ASTM G 32) and modified cavitation test. And it is also concerned with phenomenon of cavitation-erosion on the several materials. In order to compare the both test methods, cavitaion weight loss and rate of the several materials in fresh-water and sea-water measured and observed with digital camera.

Sign in / Sign up

Export Citation Format

Share Document