Runner Outlet Research Articles

Francis Turbine Blade Design on the Basis of Port Area and Loss Analysis

In this study, a Francis turbine with specific speed of 130 m-kW was designed on the basis of the port area and loss analysis. The meridional shape of the runner was designed focusing mainly on the combination of the guide vane loss analysis and experience. The runner blade inlet and outlet angles were designed by calculation of Euler’s head, while the port area of blade was modified by keeping constant angles of the blade at inlet and outlet. The results show that the effect of the port area of runner blade on the flow exit angle from runner passage is significant. A correct flow exit angle reduces the energy loss at the draft tube, thereby improving the efficiency of the turbine. The best efficiency of 92.6% is achieved by this method, which is also similar to the design conditions by the one dimension loss analysis.

JBBM at 21: Theme Reflections One Year Later, with a Design View of B-to-B Marketing Field and Closing Tribute to David T. Wilson

ABSTRACTPurpose: The purpose of this article is to acknowledge the contribution and significance of the manuscripts published in the 2015 double issue of the Journal of Business-to-Business Marketing celebrating its 21st. anniversary. A precis of each articles’ contribution is highlighted. The author explores the distinct and relevant themes that marked the orientation and positioning of the journal as the premier specialized front runner outlet in the business-to-business (B-to-B) domain and provides reflections about what is next. Finally, further recognition of David T. Wilson as founder of the JBBM, his role as educator and his teaching are remembered.Methodology/approach: A content analysis on each of the manuscripts was performed in an attempt to identify central themes, orientations, findings, and recommendations. The approach is qualitative and focused on identifying common voices from the authors that provide light to the sustainability and relevancy of the JBBM in the future. And, my reflections are enmeshed with my participant observer status as a bonafide B-to-B scholar.Findings: The JBBM has succeeded by proposing new theoretical frameworks, conceptual spaces, appropriate methodologies, and an overall rigor to a variety of themes, problems identified by the business community, international contexts, and cross functional perspectives. Our understanding of B-to-B problems, and the marketing concerns of practitioners and industry have improved but still has challenges related to value, relevancy, validity, practical implications, and usefulness to managers and industry.Research implications: As an applied field, B-to-B has borrowed theoretical frameworks and perspectives from other disciplines. It is clear that a more conceptual refinement is needed. Now is the time to organize our findings, thoughts, propositions, and observations. It may be necessary to create venues that allow for a more intense dialogue between the academic and business community. Some of these partnerships are conducted within the framework of research institutes, centers, alliances with regional and national chambers and professional associations, practitioner forums, executive training, and alliances within ecosystems networks and others. I suggest that we focus more on the “exploration” of concepts and particular organizational realities rather than on the theory testing alone. Researchers in B-to-B may require an immersion and evaluation of the situational relevancy (deep dive and thick descriptions) through an experiential validation process, interpretation, and “being there.”

Modelling and optimization of the velocity profiles at the draft tube inlet of a Francis turbine within an operating range

ABSTRACTOperating hydraulic turbines over an extended range of discharge values requires an optimized runner that minimizes the weighted-average draft tube losses. It is shown that the draft tube losses can be minimized before actually designing the (new or refurbished) runner blades by optimizing the runner outlet flow. For this, a new runner surrogate model is introduced, where the relative flow angle is expressed via the so-called swirl-free velocity profile (represented with two parameters). Given a swirl-free velocity profile, as well as a turbine discharge value, the model provides swirling flow profiles consistent with the hydraulic turbine operation. With this swirling flow as inlet condition, the draft tube flow computation provides the relationship between the swirl-free velocity parameters and the hydraulic loss. It is shown that this approach can be used for optimizing the runner for a range of turbine operating regimes.

The Design Method of Axial Flow Runners Focusing on Axial Flow Velocity Uniformization and Its Application to an Ultra-Small Axial Flow Hydraulic Turbine

We proposed a portable and ultra-small axial flow hydraulic turbine that can generate electric power comparatively easily using the low head of open channels such as existing pipe conduits or small rivers. In addition, we proposed a simple design method for axial flow runners in combination with the conventional one-dimensional design method and the design method of axial flow velocity uniformization, with the support of three-dimensional flow analysis. Applying our design method to the runner of an ultra-small axial flow hydraulic turbine, the performance and internal flow of the designed runner were investigated using CFD analysis and experiment (performance test and PIV measurement). As a result, the runners designed with our design method were significantly improved in turbine efficiency compared to the original runner. Specifically, in the experiment, a new design of the runner achieved a turbine efficiency of 0.768. This reason was that the axial component of absolute velocity of the new design of the runner was relatively uniform at the runner outlet in comparison with that of the original runner, and as a result, the negative rotational flow was improved. Thus, the validity of our design method has been verified.

Determination and generalization of the effects of design parameters on Francis turbine runner performance

ABSTRACTThe runner design is the most challenging part of the turbine design process. Several parameters determine the performance and cavitation characteristics of the runner: the metal angle (flow beta angle), the alpha angle, the blade beta angle, the runner inlet and outlet diameters, and the blade height. All of these geometrical parameters need to be optimized to ensure that the head, flow rate and power requirements of the system are met. A hydraulic designer has to allocate time to optimize these parameters and should be experienced in carrying out the iterative design process. In this article, the turbine runner parameters that affect the performance and cavitation characteristics of designed turbines are examined in detail. Furthermore, turbines are custom designed according to the properties of hydroelectric power plants; this makes the design process even more challenging, as the rotational speed, runner geometry, system head and flow rate vary for each turbine. The effects of the design parameters are examined for four different turbine runners specifically designed and used in actual power plants in order to obtain general results and generalizations applicable to turbine design aided by computational fluid dynamics (CFD). The flow behavior, flow angles, head losses, pressure distribution, and cavitation characteristics are computed, analyzed, and compared. To assist hydraulic designers, the general influences of these parameters on the performance of turbines are summarized and empirical formulations are derived for runner performance characterization.

Optimization of hydraulic turbine diffuser

Hydraulic turbine diffuser recovers pressure energy from residual kinetic energy on turbine runner outlet. Efficiency of this process is especially important for high specific speed turbines, where almost 50% of available head is utilized within diffuser. Magnitude of the coefficient of pressure recovery can be significantly influenced by designing its proper shape. Present paper focuses on mathematical shape optimization method coupled with CFD. First method is based on direct search Nelder-Mead algorithm, while the second method employs adjoint solver and morphing. Results obtained with both methods are discussed and their advantages/disadvantages summarized.

Study of the vortex-induced pressure excitation source in a Francis turbine draft tube by particle image velocimetry

Francis turbines operating at part-load experience the development of a precessing cavitation vortex rope at the runner outlet, which acts as an excitation source for the hydraulic system. In case of resonance, the resulting pressure pulsations seriously compromise the stability of the machine and of the electrical grid to which it is connected. As such off-design conditions are increasingly required for the integration of unsteady renewable energy sources into the existing power system, an accurate assessment of the hydropower plant stability is crucial. However, the physical mechanisms driving this excitation source remain largely unclear. It is for instance essential to establish the link between the draft tube flow characteristics and the intensity of the excitation source. In this study, a two-component particle image velocimetry system is used to investigate the flow field at the runner outlet of a reduced-scale physical model of a Francis turbine. The discharge value is varied from 55 to 81 % of the value at the best efficiency point. A particular set-up is designed to guarantee a proper optical access across the complex geometry of the draft tube elbow. Based on phase-averaged velocity fields, the evolution of the vortex parameters with the discharge, such as the trajectory and the circulation, is determined for the first time. It is shown that the rise in the excitation source intensity is induced by an enlargement of the vortex trajectory and a simultaneous increase in the precession frequency, as well as the vortex circulation. Below a certain value of discharge, the structure of the vortex abruptly changes and loses its coherence, leading to a drastic reduction in the intensity of the induced excitation source.

CFD study on prediction of vortex shedding in draft tube of Francis turbine and vortex control techniques

Francis Turbine when operated at part load suffers flow instability due to swirl component of the velocity attached with exiting flow downstream the runner. The swirling flow at runner outlet generates corkscrew-shaped draft tube vortex invites undesirable flow features like pressure pulsation, fluctuation in torque, axial and radial forces and structure vibration causing the turbine. This paper presents the results obtained from the numerical analysis regarding prediction of unsteady vortex behavior at the draft tube and flow instabilities specific to Francis hydro turbines occurring at the part load operating regime, using ANSYS CFX. The RNG k-ε turbulence model is adopted for turbulence treatment and better prediction of the non-cavitating vortex core and its effects. A single part-load operating condition is chosen to analyze the vortex breakdown. To minimize vortex shedding and flow instability, two vortex control techniques viz. Misaligned Guide Vanes (MGVs) and J-grooves in draft tube are evaluated numerically. Two different MGV angles were selected and four different depths of J-grooves were analyzed separately to see their effect on flow features. The use of MGV did not help much in minimizing swirl intensity whereas the use of J-groove showed better swirl control and flow enhancement in the draft tube.

Numerical Investigation of Cavitation Improvement for a Francis Turbine

Cavitation in hydraulic machine is undesired due to its negative effects on performances. To improve cavitation performance of a Francis turbine without the change of the best efficiency point, a model runner geometry optimization was carried out. Firstly, the runner outlet diameter was appropriately increased to reduce the flow velocity at runner outlet region. Then, to avoid the change of the flow rate at the best efficiency point, the blade shapes were carefully adjusted by decreasing the blade outlet angles and increasing the blade wrap angles. A large number of the modified runners were tested by computational fluid dynamic (CFD) method. Finally the most appropriate one was selected, which has the runner outlet diameter 10% larger, the blade outlet angles 3 degrees smaller and the blade wrap angles 5 degrees larger. The results showed that the critical cavitation coefficient of the model runner decreased at every unit rotational speed after the optimization, and the effect was much remarkable at relative high flow rate. Besides, by analysing the internal flow field, it was found that the zone of the low pressure on pressure surface of the optimized turbine blades was reduced, the backflow and vortex rope in draft tube were reduced, and the cavitation zone was reduced obviously.

The numerical research of runner cavitation effects on spiral vortex rope in draft tube of Francis turbine

The spiral cavitating vortex rope developed in the draft tube of Francis turbine under part load condition maybe causes serious pressure fluctuations and power swings, which threatens the safety and stability of the power plant operations. Many works have been performed to explore the mechanisms of it. In this paper, the runner cavitation and spiral vortex rope under part load conditions were studied to investigate the relations of runner cavitation and the spiral vortex rope. The results proved the existence of obvious interaction between them. The swirl flow at the runner outlet plays an important role in the formation of vortex rope. And the periodic procession of vortex rope in turn intensifies the uneven pressure distribution near the runner outlet and causes the asymmetric cavitation on the runner blades, which then give rise to the modification of swirl flow at the runner blades and thereby affects the characteristics of vortex rope.

Experimental Investigation of the Interblade Flow in a Kaplan Runner at Several Operating Points Using Laser Doppler Anemometry

This paper presents laser Doppler anemometry (LDA) measurements within the runner blade channels and at the runner outlet of a Kaplan turbine model. The model was investigated at six operating points located on two propeller curves of the turbine to study the flow condition during on-cam and off-cam operations. Main and secondary flows within and after the runner were analyzed, and the effects of the hub and tip clearances on the velocity fields within and after the runner were evaluated. Operation of the turbine at flow rates that are lower than the designed rate for the corresponding propeller curve resulted in vortex breakdown and the formation of a rotating vortex rope (RVR). The RVR formation produced an asymmetrical velocity distribution within and after the runner. The results demonstrated the occurrence of an oscillating flow with the same frequency as the vortex rope within the blade channels located upstream of the RVR. This results in an asymmetric flow through the runner and oscillating forces on the runner blades. The measured velocities indicated that the geometrical asymmetries in the runner manufacturing process resulted in various flow asymmetries at the measured sections. The asymmetries were up to 3% within the runner and 7% at the runner outlet.

Computational fluid dynamics simulation and geometric design of hydraulic turbine draft tube

Any hydraulic reaction turbine is installed with a draft tube that impacts widely the entire turbine performance, on which its functions are as follows: drive the flux in appropriate manner after it releases its energy to the runner; recover the suction head by a suction effect; and improve the dynamic energy in the runner outlet. All these functions are strongly linked to the geometric definition of the draft tube. This article proposes a geometric parametrization and analysis of a Francis turbine draft tube. Based on the parametric definition, geometric changes in the draft tube are proposed and the turbine performance is modeled by computational fluid dynamics; the boundary conditions are set by measurements performed in a hydroelectric power plant. This modeling allows us to see the influence of the draft tube shape on the entire turbine performance. The numerical analysis is based on the steady-state solution of the turbine component flows for different guide vanes opening and multiple modified draft tubes. The computational fluid dynamics predictions are validated using hydroelectric plant measurements. The prediction of the turbine performance is successful and it is linked to the draft tube geometric features; therefore, it is possible to obtain a draft tube parameter value that results in a desired turbine performance.

Effect of Air Layer on the Performance of an Open Ducted Cross Flow Turbine

Recently, the cross flow turbines attract more attention for their good performance over a large operating regime at off design point. This study employs a very low head cross flow turbine, which has open inlet duct and has barely been studied before, to investigate the performance of the cross flow turbine with air suction from the rear part of the runner. Unlike conventional cross flow turbines, a draft tube is attached to the outlet of runner to improve the turbine performance. Water level and pressure in the draft tube are monitored to investigate the influence of air suction. Torque at local blade passage of three parts of runner is examined in detail under the conditions of different air suction. Consequently, it is found that with proper air suction in the runner chamber, the water level in the draft tube gradually drops to Stage 2 of the runner and the efficiency of the turbine can be raised by 10%. Overall, the effect of air-layer on the performance of the turbine is considerable.

Steady and unsteady numerical simulations of the flow in the Tokke Francis turbine model, at three operating conditions

This work investigates the flow in the scale model of the high-head Tokke Francis turbine at part load, best efficiency point and high load, as a contribution to the first Francis-99 workshop. The work is based on the FOAM-extend CFD software, which is a recent fork of the OpenFOAM CFD software that contains new features for simulations in rotating machinery. Steady-state mixing plane RANS simulations are conducted, with an inlet before the guide vanes and an outlet after the draft tube. Different variants of the k-ϵ and k-ω turbulence models are used and a linear explicit algebraic Reynolds stress model is implemented. Sliding grid URANS simulations, using a general grid interface coupling, are performed including the entire turbine geometry, from the inlet to the spiral casing to the outlet of the draft tube. For the unsteady simulations, the k-ω SSTF model is implemented and used in addition to the standard k-ϵ model. Both the steady and unsteady simulations give good predictions of the pressure distribution in the turbine compared to the experimental results. The velocity profiles at the runner outlet are well predicted at off-design conditions. A strong swirl is however obtained at best efficiency point, which is not observed in the experiments. While the steady-state simulations strongly overestimate the efficiency, the unsteady simulations give good predictions at best efficiency point (error of 1.16%) with larger errors at part load (10.67%) and high load (2.72%). Through the use of Fourier decomposition, the pressure fluctuations in the turbine are analysed, and the main rotor-stator interaction frequencies are predicted correctly at all operating conditions.

The Impacts of Head Loss on the Bulb Turbine’s Hydropower Utilization and Running Performance

Because of the truth that the earth resources become increasingly tense, Low-head bulb turbine group was relatively fast developed and constructed in a time.The number of its running on the various types of rivers has reached a certain degree.However,its main problems are water utilization and running performance are not optimal.Its stand-alone capacity is small,therefore the problem has not attracted attention in the academia.In this paper,we based on the typical bulb turbine as the research object,using UG to the whole flow passage of mathematical modeling,based on the model of the operating characteristic curve, through Ansys software analyzes unit internal flow field calculation,and found that in a combination of guide vane and the blade opening, the head loss is the major cause of water can not efficient conversion.When increase the effective water head,can improve the output and efficiency of unit. Further analysis of the whole flow passag，the runner outlet flow patterns and the runner blade pressure,finding that the conditions can improve the turbines running performance at the same time.In the real machine test and long running practice, the above calculation results were verified. DOI : http://dx.doi.org/10.11591/telkomnika.v12i4.4891

Pressure measurements and high speed visualizations of the cavitation phenomena at deep part load condition in a Francis turbine

In a hydraulic power plant, it is essential to provide a reliable, sustainable and flexible energy supply. In recent years, in order to cover the variations of the renewable electricity production, hydraulic power plants are demanded to operate with more extended operating range. Under these off-design conditions, a hydraulic turbine is subject to cavitating swirl flow at the runner outlet. It is well-known that the helically/symmetrically shaped cavitation develops at the runner outlet in part load/full load condition, and it gives severe damage to the hydraulic systems under certain conditions. Although there have been many studies about partial and full load conditions, contributions reporting the deep part load condition are limited, and the cavitation behaviour at this condition is not yet understood. This study aims to unveil the cavitation phenomena at deep part load condition by high speed visualizations focusing on the draft tube cone as well as the runner blade channel, and pressure fluctuations associated with the phenomena were also investigated.

Hydro-acoustic resonance behavior in presence of a precessing vortex rope: observation of a lock-in phenomenon at part load Francis turbine operation

Francis turbines operating at part load condition experience the development of a cavitating helical vortex rope in the draft tube cone at the runner outlet. The precession movement of this vortex rope induces local convective pressure fluctuations and a synchronous pressure pulsation acting as a forced excitation for the hydraulic system, propagating in the entire system. In the draft tube, synchronous pressure fluctuations with a frequency different to the precession frequency may also be observed in presence of cavitation. In the case of a matching between the precession frequency and the synchronous surge frequency, hydro-acoustic resonance occurs in the draft tube inducing high pressure fluctuations throughout the entire hydraulic system, causing torque and power pulsations. The risk of such resonances limits the possible extension of the Francis turbine operating range. A more precise knowledge of the phenomenon occurring at such resonance conditions and prediction capabilities of the induced pressure pulsations needs therefore to be developed.This paper proposes a detailed study of the occurrence of hydro-acoustic resonance for one particular part load operating point featuring a well-developed precessing vortex rope and corresponding to 64% of the BEP. It focuses particularly on the evolution of the local interaction between the pressure fluctuations at the precession frequency and the synchronous surge mode passing through the resonance condition. For this purpose, an experimental investigation is performed on a reduced scale model of a Francis turbine, including pressure fluctuation measurements in the draft tube and in the upstream piping system. Changing the pressure level in the draft tube, resonance occurrences are highlighted for different Froude numbers. The evolution of the hydro-acoustic response of the system suggests that a lock-in effect between the excitation frequency and the natural frequency may occur at low Froude number, inducing a hydro-acoustic resonance in a random range of cavitation numbers.

A model for precessing helical vortex in the turbine discharge cone

The decelerated swirling flow in the discharge cone of hydraulic turbine develops various self-induced instabilities and associated low frequency phenomena when the turbine is operated far from the best efficiency regime. In particular, the precessing helical vortex ("vortex rope") developed at part-load regimes is notoriously difficult and expensive to be computed using full three-dimensional turbulent unsteady flow models. On the other hand, modern design and optimization techniques require robust, tractable and accurate a-priori assessment of the turbine flow unsteadiness level within a wide operating range before actually knowing the runner geometry details. This paper presents the development and validation of a quasi-analytical model of the vortex rope in the discharge cone. The first stage is the computing of the axisymmetrical swirling flow at runner outlet with input information related only to the operating point and to the blade outlet angle. Then, the swirling flow profile further downstream is computed in successive cross-sections through the discharge cone. The second stage is the reconstruction of the precessing vortex core parameters in successive cross-sections of the discharge cone. The final stage lies in assembling 3D unsteady flow field in the discharge cone. The end result is validated against both experimental and numerical data.

Surrogate runner model for draft tube losses computation within a wide range of operating points

We introduce a quasi two-dimensional (Q2D) methodology for assessing the swirling flow exiting the runner of hydraulic turbines at arbitrary operating points, within a wide operating range. The Q2D model does not need actual runner computations, and as a result it represents a surrogate runner model for a-priori assessment of the swirling flow ingested by the draft tube. The axial, radial and circumferential velocity components are computed on a conical section located immediately downstream the runner blades trailing edge, then used as inlet conditions for regular draft tube computations. The main advantage of our model is that it allows the determination of the draft tube losses within the intended turbine operating range in the early design stages of a new or refurbished runner, thus providing a robust and systematic methodology to meet the optimal requirements for the flow at the runner outlet.

Experimental and numerical investigation of unsteady behavior of cavitating vortices in draft tube of low specific speed Francis turbine

At both partial and full load of Francis turbines, the unsteady behavior of cavitating draft tube vortices occurs and leads to undesirable matters such as power house vibration, noise and power swing in some cases. This paper presents the investigation of the interaction between the flow pattern at runner outlet and the unsteady behavior of cavitating vortices in draft tube with experimental and numerical approaches. On the experimental research, the pressure pulsation in the draft tube is measured and the unsteady behavior of cavitating vortices is taken pictures with a high speed camera in the model test. On the numerical research, by Computational Fluid Dynamics (CFD) adopting a two-phase unsteady analysis, the analysis domain from the guide vane to the draft tube is carried out for investigating the interaction between the runner outlet flow and the vortex pattern. The pressure pulsation at the upper draft tube and the unsteady behavior of cavitating vortices obtained from CFD results are similar to those obtained in the model test. Detailed analysis of CFD results at overload indicates the repeat of expansion and contraction of cavitating vortices, which were shaped helical vortices with opposite direction of runner rotation, and the corresponding flow pattern in every time step of the pressure pulsations.