Liquid-solid Impact Research Articles

Dynamic wetting characteristics of two droplets impacting a spherical dust particle

The removal of dust based on water misting is one of the most effective measures for dust control, and the basis of this method lies in the liquid–solid impact behavior. To further improve the dust removal efficiency, in this work, the removal mechanism was studied at the microscopic level, and the dynamic impact between two water droplets and a spherical dust particle was simulated using the coupled level-set/volume-of-fluid (CLSVOF) method. The optimal parameter ranges for micron-level dust removal were determined through the method of variable control, and the reliability of the obtained results was experimentally verified. When two droplets continuously or simultaneously impact a spherical particle, the liquid film formed undergoes deformation phenomena such as fusion, rupture, stretching, contraction, and fragmentation. The liquid film is more likely to break at higher droplet velocities, leading to the filling of the gas film and hindering the wetting process. The optimum contact angle and velocity range of the liquid droplets to completely encapsulate the dust particles were found to be θ = 2 and V = 10–20 m/s, respectively. The experimental results also showed that for the same dust particle size, the dust removal efficiency initially increased but then decreased with increasing dust concentration. The optimum dust removal efficiency of 98.1 % was achieved for θ = 2 and V = 10 m/s. This study sheds new light on the dust removal mechanism of water mist-based dust removal technologies and can aid in the design and parameter optimization of more effective dust suppression systems.

Liquid–Solid Impact Mechanism, Liquid Impingement Erosion, and Erosion-Resistant Surface Engineering: A Review

Liquid impingement erosion has been known as mechanical degradation, where the original material is removed progressively from a solid surface due to continued exposure to impacts by high-speed liquid droplets. This is a major issue in many industries, including aerospace and aviation and power generation, particularly gas and steam turbines, nuclear power plants, and wind energy. Tremendous numerical and experimental studies have been performed so far to understand the physical phenomena involved in this process and to improve the erosion resistance of different surfaces. In this review paper, first, the liquid–solid impact in a wide range of relative velocities is reviewed fundamentally. Then, the liquid impingement erosion of metals, including damage regimes and damage accumulation mechanisms, as well as the role of solid properties on erosion performance are explained. Finally, promising water droplet erosion-resistant materials and surface treatments are discussed. This review paper is intended to summarize the present knowledge of the different mechanisms involved in the liquid impingement erosion process.

An equivalent method of jet impact loading from collapsing near-wall acoustic bubbles: A preliminary study

Cavitation damage is a micro, high-speed, multi-phase complex phenomenon caused by the near-wall bubble group collapse. The current numerical simulation method of cavitation mainly focuses on the collapse impact of a single cavitation bubble. The large-scale simulation of the cavitation bubble group collapse is difficult to perform and has not been studied, to the best of our knowledge. In this study, the equivalent model of impact loading of acoustic bubble collapse micro-jets is proposed to study the cavitation erosion damage of materials. Based on the theory of the micro-jet and the water hammer effect of the liquid–solid impact, an equivalent model of impact loading of a single acoustic bubble collapse micro-jet is established under the principle of deformation equivalence. Since the acoustic bubbles can be considered uniformly distributed in a small enough area, an equivalent model of impact loading of multiple acoustic bubble collapse micro-jets in a micro-segment can be derived based on the equivalent results of impact loading of a single acoustic bubble collapse micro-jet. In fact, the equivalent methods of cavitation damage loading for single and multiple near-wall acoustic bubble collapse micro-jets are formed. The verification results show the law of cavitation deformation of concrete using equivalent loading is consistent with that of a micro-jet simulation, and the average relative errors and the mean square errors are insignificant. The equivalent method of impact loading proposed in this paper has high accuracy and can greatly improve the calculation efficiency, which provides technical support for numerical simulation of concrete cavitation.

Anatomy of air entrapment in drop impact on a solid surface

When a drop impacts on a solid surface, a thin air film is entrapped first and later evolves into a spherical air bubble at the center inside the drop. The problem involves several complex physical processes, including two-phase fluid flow interactions, moving and deforming interfaces in space and time. In this paper, we dissect the whole air entrapment and evolution process from drop release at a certain height above the substrate to finally a spherical air bubble formation by direct numerical simulation. A detailed quantitative analysis of the various dynamic phenomena occurring at different stages is performed. The complex physical phenomena revealed by current high-fidelity numerical simulations are validated qualitatively against theoretical estimations and previous experimental observations, followed by quantitative comparisons with the theories and available experiments for the dimple, kink and air film. Finally, a new cognition of vortex ring evolution is proposed to explore further insights into the underlying physical mechanisms associated with the evolution of the entrapped air film in liquid-solid impact.

Experimental investigation on the water droplet erosion characteristics of blade materials for steam turbine

In this paper, the water droplet erosion ( WDE) characteristics of four blade materials under different high-speed liquid-solid impingement conditions are tested with the experimental steps and data processing methods in ASTM-G73. On the basis of cumulative erosion curves, the maximum erosion rate ( ERmax) is obtained to analyze the WDE resistance of the testing materials quantitatively. The effects of target surface roughness, impact angle and impact velocity on the WDE characteristics of blade materials under specific working conditions are studied. The velocity coefficients ( n) of the testing materials under high-speed liquid-solid impact are analyzed. In order to investigate the mechanism of WDE, the material failure characteristics and shallow layer hardness ( SLH) at three characteristic moments corresponding to different WDE periods, are investigated with the SEM morphology of erosion section and hardness distribution along the depth direction at the impact position. The research results can provide reference data and technical support for the structure design and material selection of steam turbine blades.

Experimental study on water droplet erosion resistance of coatings (Ni60 and WC-17Co) sprayed by APS and HVOF

In order to simulate the actual operating environment of the last stage blades of steam turbines，especially under the condition of high-speed liquid-solid impact (over 600 m/s), a new experimental rig for testing the water droplet erosion (WDE) characteristics is built, and three kinds of specimen structure adapted to different impact angles are designed. The WDE resistance of the four kinds of thermal spraying coating, which are prepared using atmospheric plasma spraying (APS) and high velocity oxygen fuel spraying (HVOF) with two kinds of alloy powder (Ni60 and WC-17Co) on the substrate material (17-4PH stainless steel), are tested using the experimental rig. In this paper, three-dimensional optical microscopy is used to obtain the morphology of WDE grooves on the target surface of different coating specimens. During the measurement process, three characteristic sections are selected, and the average profile of erosion grooves at different times are given respectively. The average area loss of the erosion section is obtained with integrating method. The cumulative loss curves are analyzed and the WDE resistance of the present coatings are compared. It is found that the HVOF-WC17Co coating is of the best WDE resistance.

Erosion of a multistage orifice due to liquid-solid flow

Liquid-solid impact erosion represents one of the major problems affecting systems reliability in many industries including oil and gas and power generation industries. The presence of solid particles, which cannot be avoided in these systems, is the main cause of erosion failure of piping and equipment, especially downstream complex pipe fittings. The present study aims at numerically investigating the effects of flow parameters and particle size on the solid particle impact erosion in a two-stage orifice arrangement with different spacing in a carbon steel pipe. The impact erosion occurs as a result of the presence of sand particles in the water stream. Inlet flow velocity ranges from 1 to 4m/s (Re ≈ 2.5 × 104 to 105) and solid particles in the range 50–400µm are used in this study. Also, the two orifices diameter ratios ranging from 0.5 to 0.77 with a spacing of 1D and 2D are used. The numerical analysis was performed using the k-ε eddy viscosity model integrated with a discrete phase model (DPM) along with solid impact erosion correlations to predict the impact erosion features in the piping system. The results show a strong dependence of erosion rates on the orifice diameter ratio, solid particle size and bulk liquid flow velocity. The two critical erosion locations were found downstream the second orifice; namely in the recirculation and reattachment zones. The least erosion rate was found in the case of double-orifice configuration with 1D spacing. Although a high-velocity region exists in the spacing between the two orifices, very small rate of erosion was found in this region for small particles and negligible erosion for large particles Dp≥100μm. Moreover, the erosion rates were found to increase with the increase of flow velocity and with the decrease of orifice diameter ratio and solid particle size.

The effect of coating layer in liquid–solid impact problem

The repeating impacts of high-velocity water drops have an enormous effect on the mechanical properties of the base solid surface during its service. A mathematics physics model to solve the liquid–solid impact problem is built and emphasis is put on the effect of coating layer. The pressure distribution inside the water drop and the transient equivalent stress field inside the base solid are obtained by numerical simulation. The impact stress concentration presents on the solid surface and certain internal section under the surface. The coating layer on the base solid can decrease the dimensionless equivalent stress in the solid, which can be helpful to prevent the fracture of the base solid. The dimensionless equivalent stress fields in the base solid under the coating layers of various thickness (1µm, 2µm, 5µm, 10µm) are compared and the economical coating thickness suggested is about 5–10µm. The relationship between the dimensionless equivalent stress and the impact Mach number is also provided. These results based on the fundamental solution of liquid–solid impact may improve the performance of the coating layer that protects the base solid from liquid drop impact.

Sticking and splashing in yield-stress fluid drop impacts on coated surfaces

Yield-stress fluids, including gels and pastes, are effectively fluid at high stress and solid at low stress. In liquid-solid impacts, the fluid motion can be halted by the yield stress at different points of the event, and these fluids can therefore stick and accumulate where they impact, motivating several applications of these rheologically complex materials. Here, we use high-speed imaging to experimentally study liquid-solid impact of yield-stress fluids on pre-coated horizontal surfaces. With a pre-coating of the same material, we can observe large long-lifetime ejection sheets with redirected momentum which extend away from the impact location. Under critical splash conditions, sheet breakup occurs and ejected droplets can be nonspherical and threadlike due to the inability of capillary stresses to deform material above a certain lengthscale. By varying the droplet size, impact velocity, surface coating thickness, and rheological material properties, we develop appropriate dimensionless parameters and present a low-dimensional regime map of impact behaviors.

ICOPE-15-C069 A study of the effect of microstructure on liquid-solid impact

ICOPE-15-C069 A study of the effect of microstructure on liquid-solid impact

Numerical Analysis on High Speed Liquid-Solid Impact of 17-4PH Material

In this paper, anaxis-symmetry mode is set up to simulate the high speed liquid-solid impact of 17-4ph material, which is widely used inwet steam turbine bladesof the nuclear power units. The initial speed of the droplet with the diameter of 0.3mm is 400m/s. The deformation of the solid and the stress distribution variation with time are obtained via numerical method. And the variation of the pressure inside the droplet and solid target has also been analyzed in detail. In this case, the maximum pressure in the vertical direction of the solid is 1099MPa, and the maximum deformation distance of the plateis 140nm. The results provide useful supplement and reference to the high-speed liquid-solid impact theory.

Experimental Study of Laser Cladding Methods on Water Erosion Resistance to Low Pressure Blades Materials of Steam Turbine

An experimental apparatus was built to study the effects of liquid-solid impact on laser cladding processing specimens of 17-4PH stainless steel material in the present investigation. Then the result of specimens without laser surface process was compared. The impact effect on the specimens was observed using the three-dimensional digital microscope. The depth of laser cladding and substrate material caused by liquid droplet impact was studied in detail and measured. The accuracy and reliability of the experimental system and computing methods were also verified. The depth of the impact area of laser cladding specimens was distributed in the range of 0.5–1.5 μm while the 17-4PH group was distributed in the range of 2.5–3.5 μm. In contrast with specimens without laser surface processing, the material processed by laser cladding has significantly higher resistance to water erosion.

Hydrodynamic loads during water impact of three-dimensional solids: Modelling and experiments

The problem of three-dimensional liquid–solid impact is considered. A numerical method has been developed to predict the hydrodynamic loads acting on the entering body. The proposed approach is based on the Wagner theory and the boundary element method. In order to validate the numerical simulation, an original experimental study has been performed. It consists of a series of impact tests carried out with a hydraulic machine. Three specimens have been tested: an elliptic paraboloid, a wedge with conical ends and a square pyramid. An excellent agreement between theory and experiments has been observed.

Analysis of water drop erosion on turbine blades based on a nonlinear liquid–solid impact model

Water drop erosion is regarded as one of the most serious reliability concerns in the wet steam stage of a steam turbine. One of the most challenging aspects of this problem involves the fundamental solution of the transient pressure field in the liquid drop and stress field in the metal substrate, which are coupled with each other. In this paper, we first solve the fundamental problem of high-speed liquid–solid impact, both analytically and numerically, based on a nonlinear wave model. The transient pressure distribution in liquid (include shock wave) and transient stress distribution in solid are obtained for representative water drop-1Cr13 impacts, with impact speed varying from 10 m/s to 500 m/s. The relationship between the most important parameters characterizing impact and incident speed is established. With the statistics of water drop impact on the blade, a simple fatigue model is employed in this paper to obtain the lifetime map on a blade surface under typical working conditions, in terms of both impact times and operation hours. The most dangerous water drop erosion regions and operating conditions of the steam turbine blade are deduced. These results are useful for evaluating the water drop erosion mechanisms based on the fundamental solution of liquid–solid impact.

Liquid drop impact on solid surface with application to water drop erosion on turbine blades, Part I: Nonlinear wave model and solution of one-dimensional impact

Water drop erosion is regarded as one of the most serious reliability concerns in the wet steam stage of a steam turbine. The most challenging aspect of this problem involves the fundamental solution of the transient pressure field in the liquid drop and stress field in the metal substrate, which are coupled with each other. We solve the fundamental problem of high-speed liquid–solid impact both analytically and numerically. In Part I of this paper, the governing equations based on a nonlinear wave model for liquid are derived. Analytical and approximate solutions of one-dimensional liquid–solid impact are given for both linear and nonlinear models, which provide critical insights into the water drop erosion problem. Both continuous and pulsant impacts on rigid and elastic substrates are analyzed in detail. During continuous impact, the maximum impact pressure is always higher than the water hammer pressure. Upon pulsant impact and at a particular instant related with the impact duration, the maximum tensile stress appears at a certain depth below the solid surface, which can be readily related with the erosion rate. In Part II of this paper, two-dimensional (axisymmetric) liquid–solid impact is solved numerically, from which the most dangerous impact load/duration time and the most likely crack positions are deduced. Based on our recent solution of the water drop impact statistics (associated with the fluid flow in the blade channel), a comprehensive numerical study of the water drop erosion (fatigue) on a turbine blade is carried out.

Liquid drop impact on solid surface with application to water drop erosion on turbine blades, Part II: Axisymmetric solution and erosion analysis

Based on the nonlinear mathematic model and computational method of liquid drop–solid impact established in Part I, in this paper, the quasi-3-D (axisymmetric) impact process is simulated and the results are specified for water drop impact on 1Cr13, with impact speed varying from 10 to 500 m/s. When dimensionless parameters are used to describe the impact procedure, the effect of water drop size is normalized. Both the transient pressure distribution in the liquid (including shock wave) and the transient stress distribution in the solid are obtained, and the magnitude and position of the maximum equivalent stress are given. The relationship between the most important parameters characterizing impact and incident speed is established, and simple formulae are fitted for the maximum stress, influence duration time, and influence zone size. Next, water drop erosion is analyzed for repetitive impact. With the statistics of water drop impact in a typical blade channel upon full and reduced load conditions, a simple fatigue model is employed to obtain the lifetime map on the blade surface, in terms of both impact times and operation hours. The most dangerous water drop erosion regions and operating conditions of the steam turbine blade are deduced. These results are useful to evaluate the water drop erosion mechanisms based on the fundamental solution of liquid–solid impact.

Water Drop Erosion on Turbine Blades: Numerical Framework and Applications

When small droplets are formed in the wet steam stage of a steam turbine, they may impact the blade surface at a high velocity and repetitive impacts cause water drop erosion, which emerges as one of the primary reliability concerns of the turbine. We propose an effective numerical framework that couples fluid mechanics with solid mechanics. The movements of water drops in a blade channel are analyzed based on the solution of the flow field of water steam in turbine, and impact statistics such as impact frequency, velocity, and position are obtained as the working condition and particle size are varied. A nonlinear wave model is established for high velocity liquid-solid impact, from which the characteristic impact pressure in liquid and peak impact stress in solid are obtained; the solutions are then superimposed with the pathways of water particles, and a fatigue analysis is carried out to elucidate the mechanisms of water drop erosion. The lifetime map on a blade surface with two different materials (1Cr13 and Ti-6Al-4V) under typical working conditions are obtained, in terms of operation hours, and the most dangerous water drop erosion regions and operating conditions of the steam turbine are deduced.

New Fatigue Model for Service Life Assessment of Last Stage Blade in Steam Turbine Based on Liquid Corrosion and Dynamic Stress

Forced vibration and liquid corrosion are important reasons for last stage blade failure in steam turbine. In order to improve reliability of blades in wet steam stages, the dynamic stress and the liquid-solid impact stress of blade were analyzed firstly, then Neuber’s rule, rainflow counting method and improved cumulative damage rule were introduced to develop a new model to evaluate service life of last stage blade. Many factors such as manufacturing quality, metal quality and operation status were considered, so it is more reasonable for service life assessment of last stage blade. At last, the service life of a last stage blade of 680mm was analyzed and the result approximates the practical service life. It is shown the new fatigue model can give some significant data and is usable for engineering application.

Computer modeling of liquid–solid impacts

A mathematical model is formulated in the framework of the potential theory to describe the impact of a bore on a rigid wall. The solution of the resulting free-interface flow problem is numerically approximated by a tracking method of new conception. Basically, the free interface separating liquid and air is assumed to be a free fluid line. Its shape and location are tracked in time by numerically solving the evolutive equations of a set of interface node positions and potentials. The evolutive equations are derived from Bernoulli’s law and are integrated by the Crank–Nicholson method. As the shape of the computational domain evolves in time, the domain is fully re-meshed at each time step, and a new steady mixed Dirichlet–Neumann Laplacian problem is formulated and solved by applying the R T 0 mixed finite element method. This potential flow solver has been validated by simulating the liquid–solid impact of a bore against a rigid wall and comparing the numerical results with the available experimental measurements.

Assessment of electrochemical response from high alloy stainless steels during slurry impingement and single impacts to improve understanding of erosion–corrosion

AbstractErosion-corrosion by liquid-solid impact results in damage on high alloy stainless steels where slurries are transported through pipes, valves, and pumps. It is well recognised that this damage is caused by a complex combination of mechanical (impact) and electrochemical (corrosion) processes. The synergy between erosion and corrosion is significant and depends on the nature of the materials and the aqueous environment. As part of a wider study investigating the mechanisms or erosion-corrosion of high alloy stainless steels, a series of electrochemical tests under multiple particle erosion-corrosion conditions and single impact conditions have been performed. In this paper the electrochemical behaviour under slurry erosion-corrosion and the transient electrochemical response under single impact of three stainless steels (UNS S31254, UNS S32654, and UNS S32750) is assessed. The depassivation and repassivation characteristics of the surface are characterised and these results are discussed in relati...