Turbine Flow Passage Research Articles

Study of the effects of modified draft tube with inclined conical diffuser on draft tube and upstream region

Various countermeasures including geometry optimization have been proposed and proved to have a huge impact on flow filed within the draft tube in order to mitigate the vortex rope and the induced pressure fluctuations for Francis turbine under part load operation. However, the effect of these approaches on the hydro-dynamics in upstream region still remains unclear, which is of great significance for the overall performance of the unit. This study aims to explore the influences of modified draft tube with inclined conical diffuser on the pressure fluctuations in whole flow passage. The results reveal that Generation-1 and Generation-2 draft tubes are effective in alleviating pressure fluctuations resided in the draft tube, but the former one would trigger a low-frequency pressure fluctuation with higher amplitude in the runner zone. In addition, the modified draft tube has a very limited effect on the high-frequency pressure fluctuations in the guide vane and vaneless areas. To eliminate the adverse effect of inclined conical diffuser, a design with a transitional section is put forward to smoothly connect the runner zone and inclined conical diffuser. This further developed Generation-2 draft tube presents a reasonably good performance in terms of improving flow stabilities, i.e. alleviating the pressure fluctuations not only in draft tube but also in upstream region such as runner zone. This study provides reference for obtaining a better mitigating effect on pressure fluctuations in the whole turbine flow passage.

Impact of Cooling with Thermal Barrier Coatings on Flow Passage in a Gas Turbine

Inlet temperature is vital to the thermal efficiency of gas turbines, which is becoming increasingly important in the context of structural changes in power supplies with more intermittent renewable power sources. Blade cooling is a key method for gas turbines to maintain high inlet temperatures whilst also meeting material temperature limits. However, the implementation of blade cooling within a gas turbine—for instance, thermal barrier coatings (TBCs)—might also change its heat transfer characteristics and lead to challenges in calculating its internal temperature and thermal efficiency. Existing studies have mainly focused on the materials and mechanisms of TBCs and the impact of TBCs on turbine blades. However, these analyses are insufficient for measuring the overall impact of TBCs on turbines. In this study, the impact of TBC thickness on the performance of gas turbines is analyzed. An improved mathematical model for turbine flow passage is proposed, considering the impact of cooling with TBCs. This model has the function of analyzing the impact of TBCs on turbine geometry. By changing the TBCs’ thickness from 0.0005 m to 0.0013 m, its effects on turbine flow passage are quantitatively analyzed using the proposed model. The variation rules of the cooling air ratio, turbine inlet mass flow rate, and turbine flow passage structure within the range of 0.0005 m to 0.0013 m of TBC thicknesses are given.

Numerical Prediction of Runaway Characteristics of Kaplan Turbines Applying Cavitation Model

In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. This value depends on the turbine type, the operating condition, the turbine flow passage and the runner geometry, and for Kaplan turbines might 2.5 times surpass the nominal rotational speed of the runner. The runaway speed is important for evaluation of mechanical resistance of the generator rotor. The value of runaway speed is determined based on the results of the model tests upon completion of the design works related to the runner. Therefore, accurate computation of the runaway speed will improve the design process for the runner and the whole turbine unit. Given in this paper is the numerical computation of the runaway speed for a Kaplan turbine of 40 m head. Calculations were carried out for a series of steady-state operating conditions with different runner speeds and the speed at which the torque on the runner shaft is equal to zero was determined. Two approaches for numerical simulation were compared. In the first one, the flow in the turbine was simulated using 3-D RANS equations of incompressible fluid using k-ε model of the turbulence. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. Steady-state computations were carried out in computational domain that included one guide vane channel, one runner channel, the whole draft tube, and the clearances between the runner blade and the hub as well as between the blade and the runner chamber. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.

Numerical simulation of air injection in part load operating point

The operation hydro turbines in the off-design operating points is often accompanied by pressure pulsations with a large amplitude. One way to deal with such pulsations is to inject the air into hydro turbine flow passage. The aim of this work is to simulate this process. Previously we carried out calculations in frames of homogeneous incompressible three-phase «liquid – vapor – non-condensable gas» mixture model. The computational domain consisted of wicket gate, runner and draft tube. The wicket gate and runner were considered in the periodic stage approach. The results obtained were in good agreement with experimental data at full load operating point. It was shown that the calculations on the previous model failed to accurately simulate influence of air flow rate on the amplitude and frequency of pressure pulsations in part load. Therefore the part load regime is studied carefully in this work: different computational domains are considered, different solvers are used, including ANSYS CFX and CADRUN, developed at the Institute of Computational Technologies. Different models of «liquid – gas» mixture are used in the calculations, compressibility is also taken into account. The flow rate of the injected air ranged from 0.5 to 2 percent of the water flow rate. The influence of the injected air on the flow pattern, including the vortex rope, is investigated. The results obtained are compared with experimental data.

SYSTEM ANALYSIS AND SYNTHESIS OF GAS-TURBINE STAGES AERODYNAMIC PERFORMANCE

A method for system improvement of gas turbine flow-passage at the preliminary design stage is proposed. The results of 1D aerodynamic calculation is the reference information. Based on the obtained structural parametrical models a wide range of analysis, synthesis and optimization problems can be solved, as well as uncertainty quantification problem for turbine blade permissible manufacture tolerances in batch production.

Prediction of Runaway Characteristics of Kaplan Turbines Using CFD Analysis

In case of disconnection of generator from the network and failure of the governor, the rotational speed of the rotor rapidly increases and achieves maximum value, called the runaway speed. Prediction of the runaway speed at the stage of runner design would allow to select a runner considering this characteristic. Given in this paper is the numerical prediction of the runaway speed for a Kaplan turbine. Two approaches for numerical simulation were discussed. In the first one, the flow in the turbine flow passage was simulated using 3-D RANS equations of incompressible fluid using k-ε turbulence model. In the second approach, cavitation phenomena were taken into account using two-phase Zwart-Gerber-Belamri (ZGB) cavitation model. CFD calculations were carried out with using CADRUN flow solver. When setting the boundary conditions, the turbine head, being the difference of energies in the inlet and outlet cross-sections, is pre-set as a constant value, while the discharge and the runner torque are determined in the process of computation. The computed runaway speed is compared to that obtained in the model tests. It is shown that the numerical prediction of the runaway speed using the cavitation model achieves better matching with the experimental data.

Research on Method of the Flow Passage Condition Monitoring and Diagnosis for Steam Turbine

Monitoring and diagnosis of the steam turbine flow passage is the most important premise to achieve the power plant condition maintenance. The existing characteristic flow area of steam turbine changes with main steam flow and can not accurately reflect the flow passage state of steam turbine. In order to reflect the state change in turbine passage accurately, the characteristic flow area of steam turbine stage should be investigated in the same main steam flow. Because main steam flow on-line measuring method accuracy is deficient, a new method based on the exhaust pressure of IP cylinder as character parameter of main steam flow is proposed, and a correction method which takes the impact of the heat regenerative system on main steam flow into consideration is presented. Meanwhile, in the diagnostic process, the measuring result is strongly influenced by the system inevitable measuring error which directly affects the deviation between the characteristic flow area and its standard. Thus confidence intervals of characteristic flow area is given to eliminate the system errors. Finally, the actual diagnostic example in the article indicates the practicability of the method. It can be used to diagnose the flow passage of steam turbine and provide reliable basis to find out the steam turbine potential.

Numerical investigation of the condensation flow characteristics and modification optimization of a condensing steam turbine cascade

Purpose The purpose of this study is to improved the efficiency of condensing steam turbines by legitimately reforming the flow structure. It is of great significance to study the condensation flow characteristics of wet steam for optimizing the operation of condensing steam turbines. Design/methodology/approach A two-fluid model was used to study the wet steam flow in a stator cascade. The effects of the inlet temperature and pressure drop on the cascade performance were analyzed. On this basis, endwall protrusion models were set up at varied axial position on the pressure surface to evaluate the wetness control and loss under different design conditions for cascade optimization. Findings The analysis indicates that increasing the inlet temperature or decreasing the pressure drop can effectively control the steam wetness but increase the droplet radius. The increasing inlet temperature can delay the condensation and alleviate the deterioration of the aerodynamic performance of cascades. The non-axisymmetric endwall can significantly affect the distribution of steam parameters below its height and slightly reduce the droplet radius. Compared with the original stator cascade, the optimum design conditions reduce the steam wetness by 8.07 per cent and the total pressure loss by 6.91 per cent below a 20 per cent blade height. Originality/value These research results can serve as a reference for condensing steam turbine wetness losses evaluation and flow passage optimization design.

Evaluation on sediment erosion of Pelton turbine flow passage component

A rotating disc with jet nozzle experiment system is applied to study the anti-erosion performance of flow passage component matrix materials for Pelton turbine. The test condition such as sediment characteristics(concentration, hardness, mineral content), and flow velocity are designed to simulate the actual operating condition of prototype Pelton turbine. The resultant velocity in test is high to 107 ms−1. The anti-erosion performance of materials (ADB610, ZG25, 04Cr13Ni5Mo), which are used to fabricate needle and nozzle and bucket of Pelton turbine, was studied in detail on this experiment system. The experimental studies were carried on different resultant velocities and different sediment concentrations. Multiple linear regression analysis was applied to get the exponents of velocity and sediment concentration. The exponents for different materials are different. Basing on velocity exponents and concentration exponents acquired in tests, the sediment erosion prediction models for different materials were derived. Sediment erosion for different flow passage components, such as needle tip and nozzle ring and bucket of Pelton turbine in one China hydraulic power station, were evaluated on actual operating condition for different flow passage components.

Numerical simulation of wet steam transonic condensation flow in the last stage of a steam turbine

PurposeThe purpose of this paper is to study the condensation flow of wet steam in the last stage of a steam turbine and to obtain the distribution of condensation parameters such as nucleation rate, Mach number and wetness.Design/methodology/approachBecause of the sensitivity of the condensation parameter distribution, a double fluid numerical model and a realizable k-ε-kd turbulence model were applied in this study, and the numerical solution for the non-equilibrium condensation flow is provided.FindingsThe simulation results are consistent with the experimental results of the Bakhtar test. The calculation results indicate that the degree of departure from saturation has a significant impact on the wet steam transonic condensation flow. When the inlet steam deviates from the saturation state, shock wave interference and vortex mixing also have a great influence on the distribution of water droplets.Originality/valueThe research results can provide reference for steam turbine wetness losses evaluation and flow passage structure optimization design.

Designing multi-rotor tidal turbine fences

An embedded Reynolds-Averaged Navier-Stokes blade element actuator disk model is used to investigate the hydrodynamic design of tidal turbines and their performance in a closely spaced cross-stream fence. Turbines designed for confined flows are found to require a larger blade solidity ratio than current turbine design practices imply in order to maximise power. Generally, maximum power can be increased by operating turbines in more confined flows than they were designed for, although this also requires the turbines to operate at a higher rotational speed, which may increase the likelihood of cavitation inception. In-array turbine performance differs from that predicted from single turbine analyses, with cross-fence variation in power and thrust developing between the inboard and outboard turbines. As turbine thrust increases the cross-fence variation increases, as the interference effects between adjacent turbines strengthen as turbine thrust increases, but it is observed that cross-stream variation can be mitigated through strategies such as pitch-to-feather power control. It was found that overall fence performance was maximised by using turbines designed for moderately constrained (blocked) flows, with greater blockage than that based solely on fence geometry, but lower blockage than that based solely on the turbine and local flow passage geometry to balance the multi-scale flow phenomena around tidal fences.

Research on hydrodynamic performance of a tubular turbine under tidal wave condition

Tubular turbine running environment will be affected by ocean tidal wave, under the influence of the tidal wave, the hydrodynamic performance of the tubular turbine and its water-energy conversion efficiency have become the focus of our research and discussion. This paper explores the mechanism of wave-current coupling under surface fluctuations, considering the influence of tidal wave flow and gravity influence in flow field and flow characteristics of tubular turbine. The study on the performance of the influence of hydraulic characteristics of tubular turbine under the condition of wave flow has been carried out. Results show that the wave flow conditions with considering gravity leads to mechanical runner blade be damaged by tidal wave of pressure fluctuation and cyclic extrusion, causing more serious than fatigue stress damage than no wave flow condition does which make this kind of fluid machinery practical fatigue life is reduced greatly. The condition of the wave flow condition is universal, which is one of the reasons that the actual service life is always smaller than the theoretical calculation life. Considering the case of wave flow, the calculated efficiency is larger than that without considering this condition, and the difference between the two is the maximum at the optimal operating point. In the hydraulic turbine flow passage, significant pressure and velocity gradient are generated in the vertical direction due to wave action, resulting in no longer symmetrical distribution of its position. The hydraulic characteristics in the runner are obviously different from those without flow.

Flow structure and surface heat transfer from a turbine component endwall contoured using the ice formation method

Steady-state flow structure and surface heat transfer characteristics are numerically predicted for a turbine vane passage, which is contoured using the ice formation method, using ANSYS® Fluent version 12.1. Utilized are an SST turbulence closure model with a low-Reynolds formulation, along with a pressure-based approach to solve the governing equations with the SIMPLE algorithm. The solution domain is spatially discretized with a hybrid grid, created with the commercial grid generator CENTAUR™. The endwall contour shape is obtained using an IFM or ice formation method, which relies upon natural processes wherein energy dissipation and entropy production are minimized. This ice-contouring is imposed only within the vane passage, with endwall transition regions just upstream and just downstream. Particular attention is devoted to the intricate and detailed flow structural variations which are present near the endwall, both through the vane passage and downstream of the vanes. Considered are surface oil flow visualization distributions, vortex distributions, flow pathline distributions, and variations of the z-component of velocity, including their effects of ice-contoured flow structure on surface heat transfer coefficients, relative to a flat, baseline endwall for a turbine flow passage with air flow for a vane chord Reynolds number of 49,900. Results show that contouring significantly alters the endwall heat transfer coefficient distribution, with local values which are both lower and higher compared to baseline results. Such changes are strongly linked to the altered flow field due to the contouring, including changes to passage vortex advection and development.

Selection of guide vane profile for erosion handling in Francis turbines

In guide vane cascade of Francis turbine, highest acceleration occurs, which generates equivalent amount of force for work done and erosion due to instantaneous change in flow dynamics. Hence in addition to runner vane, suitable selection of guide vane profile has equal importance. Usually, NACA defined hydrofoils are used for guide vanes. Numerous options are available, but selection of best one for optimum energy harness is important. Primarily, guide vane torque and turbine efficiency is prioritized. For the turbines operating in sediment laden water, pressure difference between two sides of guide vane and erosion resistivity are additional factors to be considered. This work was performed in the vicinity of guide vane profile selection for Francis turbines operating in sediment laden water. Computational analysis on turbine flow passage and experimental study with Rotating Disc Apparatus were performed in order to identify suitable profile. Unsymmetrical profiles were found to be better handling erosion maintaining consistency in turbine performance.

ICOPE-15-C022 Fault diagnosis for steam turbine flow passage using EMD-KPCA feature extraction and support vector machine

ICOPE-15-C022 Fault diagnosis for steam turbine flow passage using EMD-KPCA feature extraction and support vector machine

Optimization Study of Shaft Tubular Turbine in a Bidirectional Tidal Power Station

The shaft tubular turbine is a form of tidal power station which can provide bidirectional power. Efficiency is an important turbine performance indicator. To study the influence of runner design parameters on efficiency, a complete 3D flow-channel model of a shaft tubular turbine was developed, which contains the turbine runner, guide vanes, and flow passage and was integrated with hybrid grids calculated by steady-state calculation methods. Three aspects of the core component (turbine runner) were optimized by numerical simulation. All the results were then verified by experiments. It was shown that curved-edge blades are much better than straight-edge blades; the optimal blade twist angle is 7°, and the optimal distance between the runner and the blades is 0.75–1.25 times the diameter of the runner. Moreover, the numerical simulation results matched the experimental data very well, which also verified the correctness of the optimal results.

Bidirectional Power Performance of a Tidal Unit with Unilateral and Double Guide Vanes

To improve the bidirectional power performance of a tidal unit, two designs were investigated. The use of unilateral or double guide vanes in a tubular tidal unit influences the performance of the hydraulic unit. Based on the N-S equations and the RNG k-ε turbulence model, the SIMPLEC algorithm was used for 3D steady-state numerical simulation of the entire turbine flow passage with unilateral and double guide vanes. The internal flow condition under positive and reverse power generation conditions was also analyzed. At the same time, the turbine, with a runner 1.6 m in diameter, was scaled down to 0.35 m diameter for model tests. The model tests were based on a multifunction hydromechanical test bench at Hohai University. The water head, discharge, and torque of the tubular turbine were, respectively, tested using a pressure difference sensor, electromagnetic flow meter, and torque meter under different guide-vane openings. The results show that turbine efficiency in the model test is slightly lower than that predicted by numerical simulation under the same conditions. However, the difference is not large. With double side guide vanes, although the efficiency of positive power generation decreased, the efficiency of reverse power generation is greatly improved.

Experiment study on sediment erosion of Pelton turbine flow passage component material

A rotating and jet experiment system with high flow velocity is designed to study the anti-erosion performance of materials. The resultant velocity of the experiment system is high to 120 m/s. The anti-erosion performance of materials used in needle and nozzle and bucket of Pelton turbine, which is widely used in power station with high head and little discharge, was studied in detail by this experiment system. The experimental studies were carried with different resultant velocities and sediment concentrations. Multiple linear regression analysis method was applied to get the exponents of velocity and sediment concentration. The exponents for different materials are different. The exponents of velocity ranged from 3 to 3.5 for three kinds of material. And the exponents of sediment concentration ranged from 0.97 to 1.03 in this experiment. The SEM analysis on the erosion surface of different materials was also carried. On the erosion condition with high resultant impact velocity, the selective cutting loss of material is the mainly erosion mechanism for metal material.

Research on numerical method of flow-induced vibration on spiral casing structure of large-scale hydropower station

The water flow in turbine flow passage is one of the prime reasons that lead to the vibration of the spiral casing structure of large-scale hydropower station, and the fluid-structure interaction of the spiral casing structure is very complex. In this study, a numerical method it presented, which could simulate the vibration of spiral casing structure that caused by the water flow in turbine flow passage. The numerical simulation of 3-D unsteady turbulent flow through the flow passage of turbine model is accomplished by solving the N-S equations, and the flow fields of flow passage and dynamic water pressure on boundary are obtained. At the same time, the three-dimension finite element dynamic model of solid structure is established, which contain steel liner and concrete surrounding the spiral case. And then, the three-dimensional instantaneous analysis of solid are proceeded as well as the dynamic water pressure transfer real-time by user interface program on interface at which the fluid interacts with solid. The one-way coupling analysis between fluid and solid structure is realized, through which the stress field and displacement field of solid induced by water flow are obtained. At last, a case study of a spiral casing structure which located in a hydropower station in Yunnan Province is presented.

Design of Air Turbine Flow Passage and Analysis of Energy Efficiency

It is possible to use compressed air to drive air turbine, thus make the turbine drive generators to power. This paper makes a research on the feasibility of the air turbine experimental equipment with a brief introduction to its composition. The design of the nozzle flow passage and flow passage, measurement of airflow and calculation of power generation efficiency are described emphatically. Based on the result of calculation and experiment, this paper shows that the air turbine experimental equipment can generate electricity safely and steadily. Besides, measuring the efficiency of the air turbine generator set helps to promote the understanding of the engineering application of theoretical formula.