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In this paper, innovative test methods including aerodynamic acceleration, PIV measurement, separate statistics of incidence and rebound information were used to systematically investigate the rebound characteristics of flaky oxide particles and angular quartz sand impacting stainless steel at high temperature. Through the statistical analysis of a large number of experimental results and the measurement of the microscopic erosion morphology of the target surface, combined with the numerical simulation of the gas-solid two-phase flow of the test section, the intrinsic relationship between the rebound behavior of the particles and their erosion behavior was systematically explored for the first time. Meanwhile, the effects of the incident parameters, particle size and accelerated airflow on the rebound characteristics of the particles were revealed. The results have important guiding significance for further understanding the physical properties of particle-wall interaction and predicting the particle erosion characteristics and erosion distribution of industrial equipment components.

Reducing solid particle erosion of blades is one of the most urgent problems for supercritical steam turbine power generation technology. Based on the erosion rate models and the particle rebound models of blade materials obtained through accelerated erosion test under high temperature, systematic numerical simulations of the complex steam-particle flow in high pressure inlet flow channel and governing stage cascade of a supercritical steam turbine with four control valves was performed in this paper. The influence the typical nozzle chamber structure and partial-arc admission on the erosion characteristics of control stage blades was first investigated. Results show that erosion condition of nozzles in the same nozzle segment vary greatly along circumferential direction, while erosion damage to the leading edge of different circumferential rotating blades is uniform. Compared with four-valve opening condition, erosion weight-loss of the whole nozzle segment increases by 14% and 25% under three-valve opening condition and two-valve opening condition, respectively. Besides, under the partial-arc admission conditions, some large particles coming from the steam admission nozzle segment will collide back and forth between vanes and rotating blades in the downstream nozzle segment without steam admission, thus causing certain erosion to the trailing edge of nozzle suction side.

Combining an improved particle image velocimetry technique with a far-field microscope, a high-resolution quantitative measurement of the transient secondary flow field in an annular turbine cascade is conducted through moving the laser light sheet to follow the primary flow. The measuring results revealed the transient behavior and strong unsteadiness of the secondary flow in a cascade for the first time. It is confirmed that the suction side leg of the horseshoe vortex rotates around the passage vortex along the rotating direction of passage vortex. In the secondary flow of cascade, the formation, development and decay of Hopf bifurcations caused by the competition between the tensile deformation and the dissipation, have become a major behavior of vortex evolution. Driven by the interaction between the passage vortex and the suction side leg of the horseshoe vortex as well as the transverse pressure gradient, the passage vortex was pushed to the suction surface and ultimately formed the wall vortex. Furthermore, the strength of secondary vortex was enhanced with the increase of aerodynamic parameters, though the scale of vortex was gradually shrinking and the limit cycle concentrated at the core of vortex. However, no change happened to the location of vortex core and the structure of vortex. The computational fluid dynamics results revealed that the results using the SST k- ω model was the closest to the experiment results in the topological structure, the evolution process of secondary flow and the magnitude estimation, followed by those with the RNG k- ɛ model. The results with standard k- ɛ model were clearly inconsistent with the experimental results.

Based on experiments and numerical simulation, the influence of the inlet flow channel of a steam turbine on the solid particle erosion of nozzle segments was investigated systematically. The results indicate that the upstream channels of the nozzle segment, such as the regulating valve, nozzle chamber and connection pipe, concentrate the solid particle erosion to a small number of nozzles or local regions of the nozzle, which greatly reduces the time for nozzle damage. Compared with the present erosion situation, measures adopted to distribute particles at the inlet of a nozzle chamber uniformly can double the service life of a nozzle segment, while the service life can be increased by eight to ten times through measures to distribute particles uniformly at the inlet of a nozzle segment. This article shows that the service life of a nozzle segment can be doubled through substituting a nozzle chamber with a tangential steam intake for one with a normal steam intake. Moreover, a boride layer with 0.04 mm effective thickness or a CrN layer with 0.01 mm effective thickness can further double the service life of a nozzle segment. In addition, a pocket-trap arranged in the particle-aggregated area after an elbow can reduce the weight loss at nozzle sites with the most serious erosion by over 85%. These investigations are of great significance to the long-term, safe and high-efficiency running of a steam turbine.

The efficiency of the multiple nozzle oil jet pump was systematically investigated using the Mobile DTE Light Oil based on the similarity theory in experiment. The experimental condition is the same as that for the multiple nozzle oil jet pump in lubrication system of steam turbine in the power plant. Thus, the influence of the area ratio and the pressure ratio on the efficiency and the pressure ratio interval of variable conditions with stable efficiency was studied in the area ratio range of 4∼9. Results show that there is a fixed relationship between the area ratio and the pressure ratio, which leads to the high efficiency of multiple nozzle oil jet pump. However, the high efficiency value and the pressure ratio interval of variable conditions with stable efficiency show different tendencies with the changing area ratio of multiple nozzle oil jet pump. In the area ratio range of 4∼9, the pressure ratio with the high efficiency value increases by 0.03 with the decrement of 1 for the area ratio. When the area ratio is larger than 6.3, the high efficiency value increases by 1% absolutely with the area ratio decreasing by 1, but remains almost unchanged for the area ratio less than 6.3. Furthermore, the increasing area ratio widens the pressure ratio interval of variable conditions with stable efficiency. The increase of the area ratio by 1 leads to the increment of 9.7% relatively for the pressure ratio interval of variable conditions with stable efficiency. This study provides the quantitative criteria for the determination of the area ratio and the pressure ratio of multiple nozzle oil jet pump, which keeps the high and stable efficiency simultaneously. Apparently, this study has significant engineering contribution.Copyright © 2014 by ASME

Control valve is an accident prone equipment in high-parameter steam turbine, and its safety directly influences the economy and safety of the unit. In this study, a control valve of a 600 MW subcritical unit used in the power plant was investigated to reveal the mechanism of flow induced vibration of the control valve. It is found that the intermittent vibration of the control valve is a fluid-solid interaction phenomenon, which occurs in middle-opening and transonic flow condition. The phenomenon is a variable damping and nonlinear vibration for the valve stem system. The experimental results show that as the valve head tilts to different positions, the pressure fluctuation at the valve seat changes significantly at the same time. Unsteady numerical simulation is conducted when valve head is in the center and tilts toward three different directions with the same angle. The results indicate that the separation point between the high jet flow and valve head is changing with time. The thick boundary layer caused by transonic flow and the moving high-pressure region induced by impinging jet flow are the two main reasons for the flow pattern alternation. The average unbalanced force of fluid acting on valve head varies as the flow pattern alternates. And its direction is from center to the narrower side of the annular channel in the oblique section when valve head is tilted.Copyright © 2014 by ASME

Reducing solid particle erosion (SPE) of blades is one of the most urgent problems for supercritical steam turbine power generation technology. Based on the erosion rate models and the particle rebound models of blade materials obtained through the accelerated erosion test under high temperature, erosion characteristics of the first reheat stage blades in a supercritical steam turbine was simulated and analyzed by three-dimension numerical simulation method in this paper. The influence of operating conditions, particle size distribution in the inlet of nozzle and axial clearance between vanes and rotating blades on the erosion distribution of cascade were explored quantitatively. Results show that: the erosion damage of the first-reheat stage stator is mainly caused by suction surface impingement from oxide particles. In designed loading condition, small and median size of particles mainly eroded the trailing edge (TE) of nozzle pressure surface, while large particles mainly impinge the leading edge (LE) of rotating blades and the TE of vane suction surface, and erosion increase along the blade height. When the turbine is running under part-load condition, particle impingement angle on stator pressure surface is basically unchanged, while impingement velocity slightly reduced. However, the amount of particles that impinge the stator TE suction side after their first-time impingement on rotor LE increase rapidly, leading to the more severe erosion damage of stator suction surface. The particle size distribution in the inlet of nozzle has a significant effect on the erosion simulation of first reheat stage blades, and the size distribution sampled in one unit may not be used to other units. When axial clearance changes, the erosion weight loss of vane pressure surface near TE is basically held constant, while the erosion weight loss in vane suction surface near TE decreases with the increase of axial clearance. For the supercritical 600MW unit simulated in this article, the anti-SPE performance and the unit efficiency can be balanced well when the axial clearance increases to 13mm. The results in this paper will provide a technology basis for reducing oxide particle erosion in the first reheat stage blades of supercritical steam turbine.Copyright © 2014 by ASME

Reducing the solid particle erosion (SPE) of blades is one of the most important problems for high-parameter steam turbine. Based on the erosion rate models and the particle rebound models of blade materials obtained through the accelerated erosion test under high temperature, a lot of three dimension numerical simulations were conducted in this paper. The influence of particle size on the impingement point distribution on the nozzle surface and the erosion characteristics of control stage nozzle in a supercritical steam turbine were analyzed quantitatively. The size range of the oxide scale particles participating in the erosion damage were extended to 500μm, and some special anti-erosion measures corresponding to different size particles were proposed to reduce the erosion of nozzle. Results show that the erosion of pressure surface in the trailing edge of nozzle is mainly from the high-intensity impingement of particles smaller than 160μm, especially those with the size range from 20μm to 60μm. For the impingement of these small particles, optimizing the profile and cascade structure as well as coating the hard coating on the surface of nozzle can improve the erosion resistance of nozzle. However, these small particles do not impinge the nozzle trailing edge suction surface. The severe erosion damage of suction surface of nozzle was from the impingement again of the particles with the size range from 200μm to 500μm after rebounding from nozzle pressure surface. It is very difficult to resist the erosion damage of these large particles for the hard coating, and separating large particles from main steam before entering the nozzle chamber should be a good choice for improving the erosion resistance of turbine. These studies will provide a technical basis for selecting anti-erosion measures of control stage nozzle.Copyright © 2013 by ASME

Through-flow capability and flow stability of some steam turbine control valves were studied by experimental investigation and numerical simulation. Based on the analysis of thermodynamic process in control valve, the relationship of flow coefficient, area ratio of valve outlet section to seat diameter section, pressure ratio and total pressure loss coefficient was deduced, and the expression of polytropic exponent was obtained. The relative deviations between formula results and experimental results are within 3%. Both expressions can be used for design and optimization to determine control valve parameters quantitatively. The results of 3D numerical simulation indicate that the topological structure of flow fields in all control valves is similar. The results of valve stability show that the airflow force acted on the valve disc depends on the vortex strength of flow around valve stem bush and valve disc, the asymmetric transonic impinging jet under the valve disc and the diffusing action. The valve operates steadily when the inlet and outlet Mach number are less than 0.15. As the unload degree is about 85%, stem vibrates at the operating conditions when pressure ratio is less than 0.8 and opening ratio is from 10% to 18%. A multihole annular orifice can make flow steady at all operating conditions.Copyright © 2008 by ASME

This study is concerned with experiments for the relation of solid particle erosion (SPE) and the nozzle profiles. The exfoliated scale from boiler tubing results in hard particles that erode steam turbine components, especially on the control stage nozzles of high parameters turbine. To characterize SPE, solid particle trajectory is measured using particle image velocimetry (PIV) and its relation with the erosion rate of the nozzle surfaces is correlated. In addition, erosion characteristic of nozzle material is investigated by experiments and results reveal that the erosion rate is directly proportional to the impacting velocity of particles with the power of 2.31 and the maximum erosion rate is taken place at the impact angle of 20–25 degree. Furthermore, 0.5% increase in the erosion rate for every one degree of steam temperature rise is observed in the range of 839K∼883K. The erosion rate of front-loaded nozzle A is 2∼3 times higher than that of conventional design nozzle B. The life cycle of nozzle is determined by the erosion of outlet edge, and the life of nozzle B is about 5 times as long as the life of nozzle A. Based on the relation of erosion rate and nozzle profile characteristic, it can be inferred that a aft-loaded nozzle with a contoured endwall substituting a planar endwall may outperform over other nozzle profiles in anti-SPE, prolonging the life cycle of the nozzle.Copyright © 2007 by ASME