Silt Abrasion Research Articles

Effects of properties of silt particles on cavitating flow characteristics in a nozzle

To research the effects of properties of silt particles on cavitating flow, silt-laden cavitation flow in one 3D nozzle is simulated. Silt mean diameters are 0.005 mm, 0.007 mm, 0.009 mm, 0.010 mm, 0.012 mm, 0.013 mm, 0.015 mm, 0.020 mm, 0.026 mm, 0.030 mm, 0.035 mm, 0.040 mm, 0.046 mm, 0.050 mm and 0.056 mm. Silt concentrations vary from 1.0% to 10%. To measure the effects of silt particles, vapor contents under pure water cavitation flow and silt-laden cavitation flow conditions are calculated and compared. Results show that silt particles first promote the development of cavitation then inhibit the evolution of cavitation with the increase of silt concentration. Silt particles promotion scope decreases gradually and inhibition span increases constantly with the increase of silt mean diameter. Cavitation nuclei, vortices, slip velocity, virtual mass force and Saffman lift force have a closed relation with the promotion of silt particles. Vortices, viscosity and silt abrasion deeply influence the inhibition of cavitation.

Analysis of silt abrasion of the impeller ring in a centrifugal pump with J-grooves

The water flow and movement of silt in a prototype double-suction centrifugal pump was simulated using an Euler-Lagrange multiphase flow model. J-Grooves were adopted to protect the impeller ring from silt abrasion. The influence of J-grooves on the silt concentration and pump efficiency was analyzed. The results show that the radial component of the relative velocity around the impeller ring is too low to move the silt out of the spacing between the impeller plate and the casing. The high silt concentration around the impeller ring is the major contributor to silt abrasion of the impeller ring. The J-grooves induce two strong vortices, which increase the radial component of the relative velocity of water and reduce the silt concentration around the impeller ring, but additional friction losses are introduced and the pump efficiency is decreased. Optimization of the number and shape of J-grooves decreases losses in the efficiency of the pump, and effectively protects the impeller ring. Case 4 was found the most effective configuration in this study.

Numerical Simulation of Modified Trailing Edge of Francis Turbine Stay Vane Based on Solid-Liquid Two-Phase Flow

In order to investigate the silt abrasion of modified trailing edge of stay vane in Francis turbine, the numerical simulation of trailing edge with different geometries were carried out based on the solid-liquid two-phase flow by means of Computation Fluid Dynamics. The results show that low solid volume fraction distributes on the chamfered surface of trailing edge, and high solid volume fraction distributes on the end of oblique surface. The smaller the modified angle is, the larger the distribution area of high solid volume fraction is, which show the trailing edge with smaller oblique angle may suffer from silt abrasion. Therefore, in order to solve the vibration caused by Karman vortex the trailing edge has to be sharpened, the oblique angle of trailing edge should not be too small. At end of trailing edge needs to ensure a certain thickness, especially the trailing edge near the lower ring can be thicker, which can meet the anti-abrasion requirements.

Analysis of silt abrasion and blade shape optimization in a centrifugal pump

Water flow and silt movement in a double-suction centrifugal pump were simulated using an Euler–Lagrange multiphase flow model. Blade erosion rates were predicted using a particle erosion model and the influence of inlet and outlet shapes on silt abrasion was analyzed. The results show: the inlet relative velocity is larger on the suction side than on the pressure side; the blade inlet and outlet are severely silt abraded and the average erosion rate is always larger on the suction side than on the pressure side; the inlet relative velocity and the impact angle are two important influencing factors, and can be controlled by changing the inlet and outlet shapes to reduce erosion rate and increase pump efficiency. In this simulation, two effective means of reducing erosion rates are decreasing the hydraulic loss and increasing pump head and pump efficiency.

Numerical analysis of the bucket surface roughness effects in Pelton turbine

The internal flow of a Pelton turbine is quite complex. It is difficult to analyse the unsteady free water sheet flow in the rotating bucket owing to the lack of a sound theory. Affected by manufacturing technique and silt abrasion during the operation, the bucket surface roughness of Pelton turbine may be too great, and thereby influence unit performance. To investigate the effect of bucket roughness on Pelton turbine performance, this paper presents the numerical simulation of the interaction between the jet and the bucket in a Pelton turbine. The unsteady three-dimensional numerical simulations were performed with CFX code by using the SST turbulence model coupling the two-phase flow volume of fluid method. Different magnitude orders of bucket surface roughness were analysed and compared. Unsteady numerical results of the free water sheet flow patterns on bucket surface, torque and unit performance for each bucket surface roughness were generated. The total pressure distribution on bucket surface is used to show the free water sheet flow pattern on bucket surface. By comparing the variation of water sheet flow patterns on bucket surface with different roughness, this paper qualitatively analyses how the bucket surface roughness magnitude influences the impeding effect on free water sheet flow. Comparison of the torque variation of different bucket surface roughness highlighted the effect of the bucket surface roughness on the Pelton turbine output capacity. To further investigate the effect of bucket surface roughness on Pelton turbine performance, the relation between the relative efficiency loss rate and bucket surface roughness magnitude is quantitatively analysed. The result can be used to predict and evaluate the Pelton turbine performance.

Influence of dynamic seals on silt abrasion of the impeller ring in a centrifugal pump

The water flow and movement of silt in a prototype double suction centrifugal pump was simulated using an Euler–Lagrange multiphase flow model. Back-blade and J-groove configurations were adopted to protect the impeller ring from silt abrasion. Four back-blades and four J-grooves were considered. The results show that the relative velocity of water around the impeller ring is too low to move silt out of the spacing between the impeller and the casing, which results in a high silt concentration around the impeller ring. The high silt concentration around the impeller ring is the major contributor to silt abrasion of the ring. Back-blade and J-groove configurations are effective in reducing the silt concentration around the ring but extra friction loss is also introduced and the pump efficiency is decreased. Optimization of the length, position and number of back-blades, and the shape and number of J-grooves, decreases losses in pump efficiency and effectively protects the impeller ring. Case 4 for the back-blade and Case 8 for the J-groove were the most effective configurations in this study.

Mechanism and prediction of material abrasion in high-velocity sediment-laden flow

The wall surface of material is prone to silt abrasion by high-velocity sediment-laden flow. The silt abrasion is different form cavitation erosion. In this article, the characteristics of silt abrasion were discussed. The mechanism of silt abrasion was analyzed and the formation and development of ripple shape on wall surface of material were explained thereafter. Based on turbulence theory and test data, some formulas were derived for predicting the abrasion rate of concrete wall surface in high-velocity sediment-laden flow. The calculated results show good agreement with the experimental data.

Assessment of resistance of non-metallic coatings to silt abrasion and cavitation erosion in a rotating disk test rig

Hydraulic damage tests have been carried out on five types of non-metallic coating materials in slurry water. A rotating disk test rig was used to simulate silt abrasion and cavitation erosion with natural silt at periphery speeds of 30 and 40 m s −1. The resistances of the various coatings to silt abrasion, and the combination of abrasion and cavitation, have been measured and compared under specified hydraulic conditions. The tests show that among the five selected materials, epoxy resin reinforced by synthetic corundum particles and castable polyether-based polyurethane rubber were the most resistant coatings to abrasion and the combined abrasion-cavitation damage, respectively. It has also been found that of the materials tested, high elasticity polyurethane had the greatest resistance to cavitation, whilst a brittle material, epoxy resin, had the least in high-silt-content water. The erosion rates of the coatings examined were generally proportional to the peripheral speed of the disk raised to the power of 3.1–4.5 under the given conditions. The synergistic effect of cavitation and abrasion on different coating materials has been discussed.

Paleo-Periglacial Ventifact Formation by Suspended Silt or Snow—Site Studies in South Sweden

Paleo-periglacial ventifacts are common in southern Sweden. Snow and/or silt abrasion have often been suggested as the agents for ventifact formation, owing to a comparative lack of eolian sands in...

Basic Study of Coupled Damage Caused by Silt Abrasion and Cavitation Erosion : Experiments with Submerged Water Jets

Basic Study of Coupled Damage Caused by Silt Abrasion and Cavitation Erosion : Experiments with Submerged Water Jets

Basic Study of Coupled Damage Caused by Silt Abrasion and Cavitation Erosion. 2nd Report. Experiments with Water Channel.

Damage due to the coupled action of silts abrasion and cavitation erosion was experimentally studied using water channel in which artificial silt (Al2O3) were included. It was confirmed that the incipient cavitation number in silt laden water increased by 10-15% compared with that in tap water. It was shown that the magnitude of impact pressure measured by the pressure detecting films and casing vibration-acceleration had good correlation with the cavitation erosion intensity but not with the abrasive wear intensity. The damage patterns on aluminum specimens were greatly affected by the cavitation occurrence, but the amount of damaged volume was almost constant with and without cavitation. A ploughing type of abrasive wear was mainly observed on the damaged surface by scanning electron microscope.

Basic study of coupled damage caused by silt abrasion and cavitation erosion. 1st Report, Experiments with submerged water jets.

Damage due to the coupled action of cavitation erosion and silt abrasion was experimentally studied using submerged jets in which artificial silts (Al2O3) were included. It was shown that the magnitude of the acoustic emission energy, impact pressure and material damage rate caused by the cavitating jet impingement were greater than those caused by the noncavitating one. Good correlations between the above three erosion intensity parameters were also confirmed. SEM photographs of damaged surfaces showed that the edge of the abrasion trace was partially broken into pieces by cavitation. The material surface was smoother and the abrasion pattern was changed compared to that of pure abrasion.

The production and recognition of aeolian features on sand grains by silt abrasion

ABSTRACTSeveral size fractions of natural loess from Long Island, New York including sand and ventifacts were studied with the scanning electron microscope to determine if distinguishing surface features could be found. Long Island loess compares very closely to descriptions of a number of European loess deposits except for the inclusion of carbonate not found on Long Island. Ventifact and sand grain surfaces were experimentally prepared using natural loess as an abrasive agent, and compared well with those surfaces found in the natural materials. Given favourable circumstances, it is possible via scanning electron microscopy to distinguish surface features created by aeolian action in loess deposits and associated materials.