The purpose of the ''International Wet Steam Modeling Project'' is to review the ability of computational methods to predict condensing steam flows. The results of numerous wet-steam methods are compared with each other and with experimental data for several nozzle test cases. The spread of computed results is quite noticeable and the present paper endeavours to explain some of the reasons for this. Generally, however, the results confirm that reasonable agreement with experiment is obtained by using classical homogeneous nucleation theory corrected for non-isothermal effects, combined with Young's droplet growth model. Some calibration of the latter is however required. The equation of state is also shown to have a significant impact on the location of the Wilson point, thus adding to the uncertainty surrounding the condensation theory. With respect to the validation of wet-steam models it is shown that some of the commonly used nozzle test cases have design deficiencies which are particularly apparent in the context of two-and three-dimensional computations. In particular, it is difficult to separate out condensation phenomena from boundary layer effects unless the nozzle geometry is carefully designed to provide near-one-dimensional flow.
The wide use of fir-tree root and groove in turbine structures prompts the expectation to find optimum configurations, which ensure that stresses are in the safe limits to avoid mechanical failure. To perform the optimization, the reasonable characterization of root configuration is required. The existing researches characterized the fir-tree root with straight line, arc or even elliptic fillet, then the parameters of these features were defined as design variables to perform root profile optimization. However, this feature-based optimization technique yields configuration which is only optimal under the feature assumption, the question why choose these feature and whether there is a better feature modeling technique is difficult to answer. In this work, instead of the feature-based method, spline curves technique is involved to characterize the root and groove configuration, and the horizontal coordinates of the control points are selected as design variables, which are modified in the vicinity of their initial values during optimization process. The objective function is to minimize the peak stress in the root and groove regions. With the Multi-island genetic algorithm, the optimal fir-tree root configuration can be obtained with better stress distributions and low stress concentrations. The proposed spline-based optimization approach may shed lights on the conceptual design of blade root and can be easily extended to other industrial equipment design.
Experimental tests were implemented on a wet steam test rig to investigate the effects of location, shape and width of a suction slot on the water removal performance of a hollow stator blade. A straight cascade with varying outlet Mach numbers and suction pressure differences was used for the tests. The inlet flow conditions were consistent with the real running condition before the last stage stator of a 1000-MW nuclear steam turbine. Results show that the flow Mach number and suction pressure difference affect the amount of water removed. A moderate increase in the suction pressure difference triggers water film vaporisation, which decreases water removal performance. The amount of water removed continuously increases, as the slot location moves from 0.24 to 0.42 times the axial chord in the suction surface. Compared with the straight slot, the step-shaped slot cannot improve the water removal performance. On the contrary, the result is poor when the Mach number is above 0.7 because additional sharp corner leads to more serious water vaporisation. A suction slot with an arc-shaped inlet significantly improves the water removal performance by eliminating water film vaporisation under the test conditions. A 0.35-mm-width suction slot is apt to allow water film across, and a 2-mm-width suction slot cannot form an effective suction pressure difference along the slot height, both leading to poor water removal performance. Meanwhile, 0.7-and 1-mm-width suction slots promote good water removal performance, but the latter is less affected by water vaporisation.
In this study, a turbine stage together with diaphragm seals and shroud seals were chosen for numerical investigation. As the baseline design, labyrinth seals’ leakage and blade stage efficiency were analyzed firstly. The results illustrates that as a custom seal, although simplicity, reliableness, and easy replacement make labyrinth seals widely used in steam and gas turbine, but additional power loss caused by excessive leakage flow affects the efficiency of turbine. In order to enhance the efficiency of the turbine stage by leakage reduction, the labyrinth seals at diaphragm and shroud were replaced by brush seals and honeycomb seals respectively. Porous medium method was used to simulate the flow in bristle pack of brush seals, and the pressure drop in bristle was explored by Darcy law. Pressure distribution and flow field details of honeycomb seals were also researched by CFD method. Radial clearance has a direct influence on leakage, so the clearance effect was analyzed in this paper. Lastly, for the stage together with brush seals and honeycomb seals researched, results show that comparing to custom labyrinth seals, the reduction leakage was approximate 30% and the improvement of stage efficiency was 0.6%.
In addition to mechanical losses, such as interphase drag loss, braking loss and pumping loss 1 , the presence of wetness in steam turbine can also lead to many additional losses in thermodynamics, profile, shock wave and blade end, etc. The additional thermodynamics loss is caused by nonequilibrium condensing flow where the rapid-expansion pure steam will be in supercooled state, and the heat transfer process is anisothermal 2 . Many experimental and numerical investigations on nonequilibrium condensing flow have been conducted for years, where the classical condensation theory and the growth rate of water droplets have been validated and studied in Laval nozzles 3-5 and turbine cascades [6][7][8] . Moreover, experiments have been carried on in model or full-scale LP steam turbines
In order to obtain the sonic speed of the wet steam under different thermal conditions, and verify the accuracy and the precision of Petr’s wet steam sonic theory, experimental measurements were carried out. Also, the effects of acoustic frequency, pressure, wetness, and droplet size on the sonic speed of wet steam were studied based on Petr’s wet steam sonic theory. Results indicate that deviations between the experimental results and Petr’s wet steam sonic theory is in the range of −4%–4%, which is within the experimental measurement error of ±5%. The variation range of the ratio of the actual sonic speed a to the frozen speed af is 0.89–1. When the sonic speed ratio ( a/ af) is close to 1, it means that the sonic speed of wet steam is close to the frozen speed, and the faster the sound wave propagates in the wet steam. In the acoustic frequency range of 102–105 Hz, the sonic speed of wet steam increases with increase of acoustic frequency, pressure, and water droplet size, and decreases with increasing wetness.
700°C HUSC technology is considered as the next generation of more efficiently coal-fired power generation technology, the heat rate of which can be reduced by more than 8% on the basis of current ultra-supercritical units. That means there is a huge energy saving benefits. With the main steam / reheat steam temperature increasing from 600°C / 620 °C to 700°C/ 720°C, the temperature of extraction steam increases dramatically, especially the first extraction stage after reheater, the temperature of which will increase to 630 ∼ 650 °C. That means a substantial increase in the cost of the initial investment because of the nickel-based material being used in extraction pipe and heaters. With EC system, the extraction steam temperature is reduced sharply because the high temperature extraction steam is moved from the main turbine to a small parallel extraction turbine and the steam source of the small extraction turbine is from the cold reheater. So the highest extraction steam temperature will not exceed 500 °C, and the high temperature risk of heat recovery system will be eliminated completely. In this paper, exergy theory is introduced to analyze the cycle efficiency of the new thermodynamic system and the conventional one. In order to obtain a better 700 °C high ultra-supercritical thermodynamic system solution, GA method is used to optimize the regenerative system parameters to lower the overall heat consumption. The exergy theory is also used to analyze the reason why optimal solution can bring economic benefits. Finally, the feasibility of the entire system project will be analyzed.
Due to its finite size and the large centrifugal load, the fir-tree root is highly stressed, which leads to the possible early failure of the gas turbine and steam turbine. To find an optimized fir-tree root is an important issue for the design of the turbine structures. In this paper, a superellipse-based design optimization approach is proposed for the fir-tree root. Rather than the straight line and arc used in literature, the combination of the superellipse curve and line are employed to characterize the fir-tree root since the superellipse curve represents a large family of curves with limited parameters, which makes the design optimization easy and economic. For the design optimization, the objective function is to minimize the peak stress, which is a typical min-max problem with possible severe iterative oscillation and subsequent convergence difficulty. To avoid this problem, a P-norm aggregation function is proposed. The superellipse parameters are defined as design variables, while the stress concentration factor and the stress at root neck are specified as optimization constraints. With the P-series fir-tree root design as example, it is proved that our approach is effective to find the optimized configuration with better stress distribution and lower stress concentration.
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