Développement d'un modèle de cavitation à poche sur hydrofoils et hélices en régimes transitoires, implémentation sur codes potentiels et validation expérimentale

A partial sheet cavitation model has been developed and implemented in a steady two-dimensional potential flow code and in an unsteady three-dimensional potential flow code. This cavitation model uses the transpiration velocity technique to simulate the presence of the sheet cavitation. Neither an additional cavity closure model nor empirical parameters are required. Adaptable to every flow solver, the model allows a reasonably rapid simulation both in steady- and unsteady-state flow conditions for a hydrofoil or a propeller. The model is validated by comparing its results with experimental data in steady-state flow condition of a two-dimensional hydrofoil. The numerical results agree very well with the observed cavity lengths and the measured pressure distribution. As for the three-dimensional flow case, the available data in the literature allowed only the qualitative validation on the cavity length. A series of experiments in cooperation with the Bulgarian Ship Hydrodynamic Centre (BSHC) to measure the lift and drag of a hydrofoil has been then conducted for the quantitative validation of the cavitation model. The comparison results show good agreement between the experimental measurements and the numerical simulations. Finally, the cavitating propellers simulations in unsteady-state flow condition are also presented. It is shown that the partial sheet cavitation has little effect on the propeller hydrodynamic performances.Un modèle de cavitation à poche partielle a été développé et implémenté dans un code potentiel bidimensionnel stationnaire puis dans un code potentiel tridimensionnel instationnaire. L'originalité de la méthode est d'utiliser la technique des vitesses de transpiration pour simuler la présence de la poche de cavitation. Cette méthode permet une fermeture naturelle de la poche sans avoir à imposer un quelconque artifice dans le modèle ou dans la méthode de calcul. Adaptable à tout solveur de modèle d'écoulement, le modèle couplé aux codes potentiels permet, grâce à cette technique, une simulation raisonnablement rapide de l'écoulement cavitant sur un hydrofoil ou une hélice en régime d'écoulement stationnaire ou instationnaire. Le modèle a été validé par comparaison avec des essais en régime stationnaire sur un profil bidimensionnel. On retrouve numériquement les longueurs de poche observées lors des essais ainsi que les pressions mesurées. Quant à l'écoulement tridimensionnel, des résultats disponibles dans la littérature n'ont permis que la validation qualitative au niveau de la longueur de poche. Une campagne d'essais en collaboration avec le BSHC pour mesurer la portance et la traînée d'un hydrofoil a alors été effectuée avec pour objectif la validation tridimensionnelle quantitative. Les résultats obtenus montrent une bonne concordance entre les mesures expérimentales et les résultats numériques, ce qui permet de conclure de façon satisfaisante quant à la validation du modèle. Finalement, des résultats de simulations instationnaires sur des hélices en régime cavitant sont présentés. Les résultats numériques montrent que la cavitation à poche partielle affecte très peu les performances hydrodynamiques de l'hélice

Viscous effects on the hydrodynamic performance of semi-active flapping propulsor

A numerical tool based on Lattice Boltzmann Method is used to investigate viscous effects on the hydrodynamic performance of a semi-active flapping propulsor. The obtained viscous results are compared with potential flow results previously presented in literature. It is found that both numerical tools give a qualitatively good trend agreement of the open water performance at high equivalent advance numbers. The results obtained using the viscous solver are slightly lower than that of potential flow in the region where flow separation is not observed. However, in case of small equivalent advance numbers, serious flow separation occurs due to high angle of attack, and hence the viscous results yield significantly lower efficiency. In spite of the mentioned deviation in the performance predictions, the LBM results confirm that the semi-active flapping propulsor is efficient over a wide range of operating conditions. This shows a possibility to practically use such self-pitching foil as a propulsion system

Développement et validation d'un modèle de cavitation à poche sur hydrofoil et pale d'hélice

FRANCAIS Un module de cavitation à poche a été développé et implémenté sur un code potentiel hélice. La méthode pour représenter la cavitation à poche utilise les vitesses de transpiration qui permettent de dévier la condition de glissement sans modification de la géométrie. Cette modélisation permet une simulation très rapide par rapport aux différentes solutions passant par la résolution des équations de Navier-Stokes en diphasique. Le modèle est validé par comparaison avec des essais expérimentaux sur hydrofoils en 2D et en 3D. Ses performances sont également comparées à d’autres simulations numériques. ENGLISH A sheet cavitation module have been developed and applied in a BEM code for calculating propeller performance. This simulation, in order to represent the sheet cavitation, employs the transpiration velocities technique which allows the deviation of slip condition points without any modification of the geometry. The method provides a very rapid simulation compared to a two-phase Navier-Stokes simulations. The model is validated by comparison with the results of experimental trials performed on hydrofoils in 2D and 3D. Its performances are also compared with other numerical simulations

E-Engine for a Long-Tail Boat, an Application in ASEAN (Association of Southeast Asian Nations)-Design and Comparison with Internal Combustion Engine

An Electric propulsion (E-propulsion) system for ASEAN (Association of Southeast Asian Nations) long-tail boat is proposed in this article. It offers several advantages over a traditional internal combustion engine propulsion system. Besides low noise and zero-emission, characteristics of electric engine (E-engine) allow regenerative braking and starting the propeller in the water. A design of E-engine has been achieved through finite element analyses and lump-parameter thermal simulations. It shows better performances than Honda GX270 internal combustion engine in terms of volume, weight, torque, and power. A full scale prototype of E-engine was manufactured. Experiments have been conducted on an engine test bench. Torque, power, efficiency and temperatures were well aligned with the simulation results

Implementation of a transpiration velocity based cavitation model within a RANSE solver

WOSInternational audienceAtranspirationvelocitybased partial sheet cavitationmodel has previously been successfully validated when implemented within potential flow codes. The model is independent from any solver and permits to estimate the cavity length based on the subcavitating pressure distribution. This paper presents its implementation within a Reynolds Averaged Navier-Stokes Equations solver. In order to compare the results of the implementation, experimental measurements on a 2D hydrofoil and potential flow code results are used. Several stages are covered. First the geometries of the cavitation sheets computed with the potential flow code are imposed with a slippery boundary condition on its surface into the RANSE simulation. The results obtained are in very good agreement with the previous validated results. In the second stage, the Volume of Fluid module is activated and water vapour is ejected from the foil surface and the transpirationvelocities are computed with the potential flow code. The results are similar but the length of the cavitation closure is much shorter. Finally, the model is fully implemented within the RANSEsolver. The transpirationvelocities are computed using the model from the subcavitating pressure distribution. They are then applied on the foil surface as water vapour. The results are quasi-identical to the results obtained when the transpirationvelocities are taken from the potential flow code. The paper proves the feasibility of modelling the cavitation sheet using transpirationvelocities and VOF within aRANSEsolver

A Transpiration Velocities Based Sheet Cavitation Model

NonWOSInternational audienc

Porpoising foil as a propulsion system

WOSInternational audienceA potential flow solver (BEM) is used to simulate a porpoising foil in order to compare the hydrodynamic performance of the biomimetic propulsion device with a conventional propeller. The device is assumed to move in open-water. Cavitation or ventilation phenomena are not considered. The method is first verified against the Theodorsen theory. The numerical thrust-loading coefficient is in agreement with the theory for the whole range of the Strouhal number. The effect of the heave-to-chord ratio, the maximum pitch angle and the Strouhal number are then studied. The effect of the geometry is not investigated. An optimum efficiency is found for a Strouhal number from 0.2 to 0.7, and for a maximum pitch angle between 30° and 60°. The heave-to-chord ratio has no influence on the maximum efficiency. Moreover, this parametric study demonstrates that the Strouhal number plays the same role in the oscillating wing as the advance parameter in the propeller. A general approach for the comparison of the two propulsion systems is proposed. Despite their different nature, their hydrodynamic performances are similar. Finally, comparative results of unsteady state simulations are also presented since the propeller pitch variation is analogous to a change in the foil motion

E-Engine for a Long-Tail Boat, an Application in ASEAN (Association of Southeast Asian Nations)-Design and Comparison with Internal Combustion Engine

An Electric propulsion (E-propulsion) system for ASEAN (Association of Southeast Asian Nations) long-tail boat is proposed in this article. It offers several advantages over a traditional internal combustion engine propulsion system. Besides low noise and zero-emission, characteristics of electric engine (E-engine) allow regenerative braking and starting the propeller in the water. A design of E-engine has been achieved through finite element analyses and lump-parameter thermal simulations. It shows better performances than Honda GX270 internal combustion engine in terms of volume, weight, torque, and power. A full scale prototype of E-engine was manufactured. Experiments have been conducted on an engine test bench. Torque, power, efficiency and temperatures were well aligned with the simulation results

A potential flow based underwater glider flight simulator.

International audienc