Single Hydrofoil Research Articles

Enhancing Bulb Turbine Performance Assessing Air Injection for Vibration Mitigation and Hydrofoil Cavitation

Small hydro technology is playing a crucial role in advancing sustainable, clean energy policies as part of the global hydro development strategy. Its contribution to social and economic development is becoming more prominent, particularly in ensuring electricity access for rural communities and supporting industrial expansion. The main causes of bulb turbine failures under high operating conditions are frequently attributed to variations in pressure in the draft tubes, which are aggravated when a spinning vortex rope is formed under load operation. Different fluid injection techniques, namely compressed air and water jet injection, address these issues and reduce the negative results of cavitation. The investigation covers the flow visualization on the suction side of a single hydrofoil utilizing a cavitation tunnel and a bulb turbine. This study assesses the effectiveness of compressed air injection in reducing vibration generated by cavitation in bulb turbines. Positive results of the experimental studies suggest a decrease in noise and vibration by air injection that prevents oscillations of the vortex rope. This research also considers how the hydrofoil design of bulb runner blades influences flow characteristics. Hence, it provides knowledge on cavitation structures in diverse cavitation numbers. Different studies that compare the original and modified hydrofoil designs reveal remarkable improvements that may be due to changes in the key parameters of the hydrofoil, such as later cavitation initiation and reduced intensity. To obtain the optimal output of a bulb turbine by considering air injection for vibration reduction and hydrofoil design changes to limit the negative effect of cavitation, the Reynolds number and cavitation number are to be defined. This multidisciplinary approach possesses enormous potential to increase the reliability and efficiency of bulb turbines in challenging operating conditions.

Numerical simulation of the unsteady flow mechanism and dynamic characteristics around cascade

Research on the flow mechanism and dynamic characteristics of a cascade comprising three NACA hydrofoils was conducted under varying cavitation numbers and angles of attack. This study serves as a theoretical foundation for the high-speed miniaturization of fluid machinery. Drawing upon prior findings on individual hydrofoils, comparisons were made regarding the cavitation characteristics of the cascade versus a single hydrofoil, emphasizing pressure and velocity distributions in the flow field. Results suggest that while the cascade consists of three hydrofoils, their interactions profoundly influence the flow field. The cavitation phenomena in the cascade diverge considerably from that of a single hydrofoil. Multiple hydrofoils cause a low-pressure region to appear in the middle of the cascade, making it more susceptible to cavitation flow compared to a single hydrofoil. However, interactions among the hydrofoils constrain the expansion of this low-pressure zone, rendering the cavitation flow in the cascade’s middle layer more stable. As the angle of attack rises, the cavitation flow around the cascade undergoes notable changes, with varying cavitation flows at different cascade positions. The upper layer experiences cavitation flow akin to that of a single hydrofoil. In contrast, the middle layer sustains a thin, weakly periodic cavitation flow.

Thermodynamic Suppression Effect of Cavitation Arising in a Hydrofoil in 140 °C Hot Water

Abstract The thermodynamic suppression effect of cavitation arising in a NACA0015 single hydrofoil is experimentally investigated in water at mainstream temperatures of T∞ = 20 °C to 140 °C in the present study. The cavity length at T∞ = 140 °C is shorter than that at T∞ = 20 °C at a constant cavitation number for all cavity patterns from inception to supercavitation. On the other hand, the cavity length at T∞ = 80 °C is slightly shorter than that at 20 °C in a certain region in which unsteady sheet-cloud cavitation occurs. This indicates that the thermodynamic suppression effect appears easily in unsteady cavitation. In addition, the temperature reduction inside cavities in water is accurately measured using thermistors, which are inserted from the sidewall directly into the cavity. The temperature measurement is performed at a mainstream temperature of less than 80 °C due to limitation of calibration for the sensor. The temperature reduction at 140 °C is then predicted from the measured cavity length. It is shown that the temperature reduction inside the cavity is approximately ΔT = 0.3 °C at T∞ = 80 °C and ΔT = 0.05 °C at T∞ = 20 °C under supercavitation conditions. The predicted temperature reduction inside the cavity is ΔT = 1.1 K at T∞ = 140 °C under supercavitation conditions. Finally, Fruman's prediction equation for ΔT is examined by fitting to the measured and predicted ΔT values with assuming a volume coefficient of evaporation CQ as a fitting parameter.

Energy Extraction Performance of Tandem Ground-effect Hydrofoils

To study the influence of the spatial configuration of two tandem ground-effect hydrofoils on the power-extraction efficiency, this paper uses the overset grid method to establish a two-dimensional numerical calculation model based on the STAR-CCM+ software. The comparison of the numerical results of the single hydrofoil verifies the validity of the method. This paper systematically analyzes the influence of ground effect on the energy extraction performance of the hydrofoil, and further studies the changes in the hydrodynamic performance and energy extraction efficiency of the hydrofoil when two ground effect hydrofoil are tandem. The results show that: compared with a single ordinary hydrofoil, the energy extraction efficiency of the ground-effect hydrofoil is slightly improved. When the hydrofoil is close to the wall, its lift will be significantly increased due to ground effect. When two ground effect hydrofoils are tandem with a phase difference of 180 deg, the vortex generated by the upstream hydrofoil will significantly increase the absolute lift of the downstream hydrofoil, but the energy extraction efficiency will be reduced significantly.

Analysis of Bulb Turbine Hydrofoil Cavitation

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.

Effect of convergent duct geometry on the energy extraction performance of tandem oscillating hydrofoils system

In the present study, a new hydrokinetic energy harvester concept based on the tandem oscillating hydrofoils configuration is numerically investigated. Unsteady turbulent two dimensional flow simulations were performed, by using the commercial finite volume computational fluid dynamics code FLUENT, to study the power extraction from tandem hydrofoils oscillating inside a convergent duct. A sinusoidal function was used to interpret the plunging/pitching motion of NACA 0015 hydrofoil. Computations were carried out for the different configurations of area ratios (AR) that is defined as the ratio of the upstream hydrofoil’s inlet cross section (A1) to the downstream hydrofoil’s inlet cross section (A2) ranging from 1.0 (without the convergent section) to AR = 2.6. The study revealed that the power extraction was enhanced by the increased incoming flow velocity enabled by the geometry of the convergent duct, which positively affected the total pressure as well as the hydrofoil-vortex interaction time and resulted the generation of larger vertical hydrodynamic force. Upon analysis of the obtained results, it is found that the energy extraction efficiency is improved, compared to that of the conventional tandem configuration where the hydrofoils move in an open flow space, and, as the area ratio (AR) increased, the amount of extracted power becomes higher in a proportion ranging from 4% to 80%. The concept was numerically tested for tandem and single configurations and for non-dimensional frequencies in the range of f∗=0.04 - 0.20. One interesting finding is that, due to some positive effect of hydrofoil-vortex interaction, and at a specified area ratio and frequency, the downstream hydrofoil efficiency exceeds the efficiency of a single hydrofoil located at exactly same position as the downstream hydrofoil in the tandem configuration. The frequency and the area ratio are found to be critical factors that determine whether the downstream hydrofoil-vortex interaction is favorable or unfavorable. An optimal area ratio/frequency combination results in a positive hydrofoil-vortex interaction effect and allows the downstream hydrofoil to contribute positively to the total power extraction as a single hydrofoil. Based on the present results, and for an optimal efficient energy harvester design, a new correlation is suggested in order to properly control the area ratio in accordance with the variation of the oscillating frequency leading to more power production and high performance of the oscillating tandem hydrofoils. It is anticipated that this new innovative technique will be applied to improve the existing energy harvester devices.

Experimental and numerical study of a hydrokinetic turbine based on tandem flapping hydrofoils

Abstract The energy harvesting of a hydrokinetic turbine based on tandem flapping hydrofoils is investigated experimentally and numerically. The mechanisms with crankshafts and connecting rods are adopted to convert the oscillatory motions of the hydrofoils into rotary motions. The hind hydrofoil performs oscillatory motion in the vortex flow of the fore hydrofoil. The longitudinal spacing L x between the two hydrofoils is fixed while the phase difference e between the flapping motions of the two hydrofoils can be shifted from − π to π . The global phase shift Φ , which is the combination of L x , e and the Strouhal number S t , is adopted to describe the vortex interaction modes. The effects of S t and Φ on the energy harvesting have been tested. Experimental data show that the highest hydrodynamic efficiency of single hydrofoil is 25.2 % at S t = 0.235 . The optimum parameters for the energy harvesting of tandem hydrofoils have been found. The highest hydrodynamic efficiency is found at S t = 0.24 with Φ / 2 π ≈ 0.3 . Numerical simulations are performed to study the vortex interaction modes of these typical cases. The beneficial vortex pattern and the detrimental vortex pattern, which result in the highest and lowest efficiency of the turbine, have been investigated.

Wake vortex interaction effects on energy extraction performance of tandem oscillating hydrofoils

An energy extracting technology based on tandem oscillating hydrofoils from flow field is presented in this paper. Numerical simulation were performed to optimize the spatial arrangement for tandem oscillating hydrofoils, the position of the downstream hydrofoil relative to the wake vortex shed by the upstream hydrofoil is seen as critical. Optimized position of the two hydrofoils improves the energy extraction performance through positive interactions between the downstream hydrofoil and the wake vortices of the upstream hydrofoil, and the highest energy extraction efficiency reaches 53.8%. The downstream hydrofoil has a slight impact on the energy extraction performance of the upstream hydrofoil, and the contribution from the upstream hydrofoil is usually slightly inferior to the single hydrofoil results. Leading edge vortex (LEV) is formed and shed from the upstream hydrofoil, which is seen as critical in the energy transformation between the fluid and the energy extraction device. For different reduced frequencies, the energy extraction of a single hydrofoil is heavily influenced by the dynamics of vortex forming and shedding. The investigation was also undertaken over a wide range of kinematic parameters, including hydrofoil separation distance and reduced frequency. Results reveal that energy extraction of tandem oscillating hydrofoils shows better performance than a single hydrofoil for optimal reduced frequency and suitable hydrofoil separation distance.

추력과 효율 향상을 위한 AUV Double Hydrofoil의 모션 최적설계

While most AUV researches have concerned about single hydrofoil, practical AUV's are generally operated with multiple hydrofoils. Double hydrofoil study attempts to evaluate thrust and efficiency with various flapping motions, and carries out design optimization using parametric analysis. Flow patterns such as vortex shedding and wake-body interaction are carefully investigated during design variable sensitivity analysis. The purpose of this design optimization is to find out the optimal motion that yields maximum thrust and efficiency. The design optimization employes several techniques such as table of orthogonal arrays, Kriging method, ANOVA analysis and MGA. Throughout this research, it is possible to find the optimal values of heaving ratio, heaving shift and pitch shift: Heaving ratio 0.950, heaving shift <TEX>$23.120^{\circ}$</TEX> and pitch shift <TEX>$89.991^{\circ}$</TEX> are found to be optimal values in double hydrofoil motions. Thrust and efficiency are 16.7% and 35.1% higher than existing AUV that did not consider nonlinear dependency of motion parameters. This results may offer an effective framework that is applicable to various AUV motion analyses and designs.

多重プロセス型モデルによる極低温キャビテーションの熱力学的効果の CFD 解析

We previously constructed a new cavitation model called “Multi-process Cavitation Model”, which takes the various elementary processes in cavitation into account, and farily good results were obtained for cold water cavitation while a poor result was done for a cryogenic cavitation with thermodynamic effect. In this paper, we revisited the application of this model thoroughout investigation of the model parameters. We conducted a cavitation simulation on single hydrofoil, and found that the appropriate modeling of expasion/shrinkage is rather more important than the evaporation/condensation rate that causes thermodynamic effect.

English

The paper presents a numerical method for analyzing the potential flow around two dimensional body such as single circular cylinder, NACA0012 hydrofoil and double circular cylinders by finite element method. The numerical technique is based upon a general formulation for the Laplace’s equation using Galerkin technique finite element approach. The solution of the systems of algebraic equations is approached by Gaussian elimination scheme. Laplace’s equation is expressed in terms of both steam function and velocity potential formulation. A finite element program is developed in order to analyze the result. The contours of stream and velocity potential function are drawn. The contour of stream function exhibits the characteristics of potential flow and does not intersect each other. The calculated pressure co-efficient shows the pressure decreasing around the forwarded face from the initial total pressure at the stagnation point and reaching a minimum pressure at the top of the cylinder. Key words: Stream function, velocity potential, number of nodes (NDE), number of elements (NEL).

추력 및 효율 향상을 위한 Double Hydrofoil 움직임에 대한 수치해석 연구

The motion of birds and insects have been studied and applied to MAV(Micro Air Vehicle) and AUV(Autonomous Underwater Vehicle). Most of AUV research is focused on shape and motion of single hydrofoil. However, double hydrofoil system is mostly used in real physics. This system shows completely different hydrodynamic characteristic to single hydrofoil because of wake interaction. The goal of this study is define the trajectory of wake interaction in double hydrofoil system. Moreover, trust and efficiency of various combined motion will be demonstrated. Symmetry airfoil is used for analysis an hydrodynamic characteristic. Forward wing’s plunging and pitching motion is fixed, hide wing’s Heaving ratio, Pitch phase shift from forward plunging and Heaving shift is changed. This study provide necessary basic data of motion optimization for double hydrofoil system.

추력 및 효율 향상을 위한 Double Hydrofoil 움직임에 대한 수치해석 연구

The motion of birds and insects have been studied and applied to MAV(Micro Air Vehicle) and AUV(Autonomous Underwater Vehicle). Most of AUV research is focused on shape and motion of single hydrofoil. However, double hydrofoil system is mostly used in real physics. This system shows completely different hydrodynamic characteristic to single hydrofoil because of wake interaction. The goal of this study is define the trajectory of wake interaction in double hydrofoil system. Moreover, trust and efficiency of various combined motion will be demonstrated. Symmetry airfoil is used for analysis an hydrodynamic characteristic. Forward wing`s plunging and pitching motion is fixed, hide wing`s Heaving ratio, Pitch phase shift from forward plunging and Heaving shift is changed. This study provide necessary basic data of motion optimization for double hydrofoil system.

Numerical analysis of unsteady cavitating flow by using a modification based on an assumption of apparent phase equilibrium

The prediction accuracy of cavitation by CFD is still not so high even in a simplest flow field around a single hydrofoil especially in transient condition at higher angle of attack, which is common problem in both commercial software and in-house solvers. In the transient condition, unsteady cavitation occurs, in which sheet cavity breaks off and cloud cavity sheds downstream periodically. At that time, the sheet cavity length tends to be underestimated in usual CFD. In the present study, modification for the phase change model is suggested, which is based on an idea of apparent phase equilibrium on gas-liquid interface with unsteady and disturbed flow. At first, a preliminary experiment has been done for evaporation on two gas- liquid interfaces with and without flow, the result contributes the evidence of the idea of apparent phase equilibrium with flow. In the result, the pressure around gas-liquid interface with flow was higher than that without flow on the occasion of evaporation, it means flow accelerates evaporation. I treat the gap of the pressure as a gap of phase equilibrium pressure macroscopically. Then, numerical simulation of cavitating flow around a hydrofoil is performed with a modification of phase change model in the transient condition at higher angle of attack which is most difficult to predict by the present solvers. In the modification, the gap of the pressure with and without flow is taken into account according to a value of a local variation of velocity in the cavitating flow filed. The formulation is similar to the PDF model for phase change model in cavitation by Singhal. The numerical results by the present modification are compared among few pressure variation components which are assumed to accelerate the evaporation in transient cavitation.

Accuracy validation of cavitation performance prediction for single hydrofoil by LES

Accuracy validation of cavitation performance prediction for single hydrofoil by LES

Periodical shedding of cloud cavitation from a single hydrofoil in high-speed cryogenic channel flow

In order to explain criteria for periodical shedding of the cloud cavitation, flow patterns of cavitation around a plano-convex hydrofoil were observed using a cryogenic cavitation tunnel of a blowdown type. Two hydrofoils of similarity of 20 and 60 mm in chord length with two test sections of 20 and 60 mm in width were prepared. Working fluids were water at ambient temperature, hot water and liquid nitrogen. The parameter range was varied between 0.3 and 1.4 for cavitation number, 9 and 17 m/sec for inlet flow velocity, and −8° and 8° for the flow incidence angle, respectively. At incidence angle 8°, that is, the convex surface being suction surface, periodical shedding of the whole cloud cavitation was observed on the convex surface under the specific condition with cavitation number and inlet flow velocity, respectively, 0.5, 9 m/sec for liquid nitrogen at 192°C and 1.4, 11 m/sec for water at 88°C, whereas under the supercavitation condition, it was not observable. Periodical shedding of cloud cavitation occurs only in the case that there are both the adverse pressure gradient and the slow flow region on the hydrofoil.

Fastest in the World: The Saga of Canada's Revolutionary Hydrofoils (review)

Reviewed by: Fastest in the World: The Saga of Canada's Revolutionary Hydrofoils Norman R. Ball Fastest in the World: The Saga of Canada's Revolutionary Hydrofoils. John Boileau. Halifax: Formac, 2004. Pp. 96, illus., $24.95 Fastest in the World is a fascinating but ultimately sad tale. It is also instructive. A thirty-seven-year military career as well as historical writing experience have prepared John Boileau for the task. And hydrofoils, a type of vessel in which Canada produced two world speed record holders but no significant commercial craft, have given Boileau an excellent subject. The principle of the hydrofoil had been discovered in 1861 by English aviation pioneer Thomas Moy. Instead of applying more power to push displacement hulls through the water, hydrofoils lifted the hull out of the water and skimmed along the surface. Almost fifty years later, Alexander Graham Bell and Casey Baldwin undertook the world's first sustained hydrofoil experiments at the Bell estate on the Bras D'Or Lakes, Cape Breton. On 9 September 1919, the HD-4, powered by two 350-hp Liberty aircraft engines, set the world speed record for boats at 114.01 km/hr. The boating world rejoiced, but no commercial success followed and the remains of the vessel were left to rot on a beach. Canada's next sustained foray into hydrofoils was driven by the military. It too led to a world record: 62 knots (114.7 km/hr) set by the Canadian Navy hydrofoil HMCSBras D'Or on 9 July 1971. Four months later, the federal government announced that the Bras D'Or would be laid up for five years while it supposedly reassessed needs. The project was dead. Boileau feels it was the wrong step, and it probably was. Canada had the best craft of its kind in the world, with potential for sales to NATO countries. The Canadian craft would have cost $15–$20 million each. The Americans claimed they could create a proven craft – it was actually deeply flawed – for $6.9 million. The United States got the go-ahead to do further development, backed by ten NATO countries. Then the cost skyrocketed and half the countries dropped out. For some, the Bras D'Or is another Avro Arrow story, a reflection of what Boileau calls the 'unerring [Canadian] instinct to snatch defeat from the jaws of victory.' But there is more to the story, three points that Boileau hints at, but fails to highlight. First, modern technology must be based on solid research. Bell and Baldwin were pioneers, but they failed to consider placement of the [End Page 533] hydrofoils instead of just their design. Decades later, the Canadian Navy discovered a single hydrofoil at the front with the dual hydrofoils at the back worked better. Also, the diesel engines chosen were unreliable and undercut Canada's efforts. Second, although the Canadians had the best technology, superior technology is not always enough. The Canadians trusted allies who didn't have their interests at heart. The British and Americans did not want Canada to develop military production capability that would cut into their lucrative sales. Canadians should have spent more time skulking in the corridors of power and cutting backroom deals. Third, long-term R&D projects are not for the short-sighted and faint of heart. The hydrofoil story represents the defeatist attitude of 'If they place orders for it, we will build it.' The situation needed more of the attitude 'If we build it, they will come.' Boileau's Fastest in The World rekindled the pride I felt as a young Canadian when people all around the world marvelled at a revolutionary Canadian ship. But it also raises painful unanswered questions. Why are Canadian businesspeople, politicians, and policy-makers not benefiting from some of the more obvious insights of history? Do historians have more to offer business and government than pretty books? [End Page 534] Norman R. Ball University of Waterloo Copyright © 2007 University of Toronto Press

Hydrodynamic optimization of performance of blunt ships

Abstract Various research works on hydrodynamic performance of the general streamlined ships in the domain of ship fluid mechanics have been implemented during the past several decades. However, as to those special types of ship, say, the blunt ship, relevant investigative work is never put on the top of the agenda. This paper and the subsequent work would like to deal with a representative kind of blunt ship, the dumb barge. It is expected that the research work can supply a gap in the weakness of study on the blunt ships. The drags and flow fields of the dumb barge models are numerically calculated by solving the RANS (Reynolds Averaged Navier-Stokes) equations associated with the RNG (ReNorma- lization Group) k-ɛ turbulence model and the VOF (Volume Of Fluid) model. The comparisons of the calculated drags with that of experimental data from towing tank shows that hydrodynamic performance of the dumb barge can accurately be predicted by numerical calculations. On the basis of the aforementioned numerical calculations, the work turns to the hydrodynamic stability of the barge. Theoretically speaking, the faster the barge moves on the water surface, the greater the trim angle. This means the barge would lose its hydrodynamic stability when it goes faster and faster. To overcome this difficulty, it occurs to us that the hydrodynamic stability of the barge at high speed may be improved by some appendages on the hull. Then two experiments are carried out, respectively, for two styles of hydrofoils with the same profile. The first twin hydrofoils are symmetrically put on the two sides of the hull and the second single hydrofoil below the bottom of the hull. At a series of steady speeds of the barge, every group of experiments includes two aspects of information, the drags and the trim angles. The experimental results indicate that the hydrofoils effectively control the flow fields around the appendaged barges.

Development of a cavitation erosion model

A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A thin copper foil, applied to the surface of the hydrofoils, was used as an erosion sensor. The cavitation phenomenon on hydrofoils at different flow conditions (system pressure, water gas content, flow velocity) was observed. Results that showed a significant relationship between cavitation erosion and the visual effects of cavitation made it possible to use these information to develop a cavitation erosion model. The model is based on the physical description of different phenomena (cavitation cloud implosion, pressure wave emission and its attenuation, micro-jet formation and finally pit formation), which are involved in the process of pit formation. It is capable to predict the influence of significant parameters as flow velocity and gas content of water. The model that was developed on the basis of measurements of cavitation on a single hydrofoil was later tested on an actual hydraulic machine in the form of a radial pump. The predicted magnitude and distribution of cavitation damage relates well to the experimentally measured one.

Relationship between cavitation structures and cavitation damage

A study of visual and erosion effects of cavitation on simple single hydrofoil configurations in a cavitation tunnel was made. A two-dimensional hydrofoil with circular leading edge was used for the experiments. In addition, the hydrofoil geometry was modified to obtain some three-dimensional cavitation effects. A thin copper foil, applied to the surface of the hydrofoil, was used as an erosion sensor. Cavitation phenomenon above hydrofoils at different flow conditions (system pressure, water gas content) was observed. Images of vapour cavities from above and from side view were taken. A statistical evaluation of cavitation structures was made. Images of damaged copper coated hydrofoil surface were taken under sufficient magnification. A pit-count method, based on computer-aided image processing, was used for direct measurement of the cavitation erosion by evaluating the damage of the surface of the hydrofoil. A relation between characteristics of cavitation structures and cavitation damage was established.