Dimensional Hydrofoil Research Articles

Quasi-periodic forces and conditionally averaged characteristics of unsteady cavitation flow around a hydrofoil

Large-eddy simulations are performed to investigate the cavitating flow around two dimensional hydrofoil section with angle of attack of 9° and high Reynolds number of 1.3×106. We use the Schnerr-Sauer model for accurate phase transitions modelling. Instantaneous velocity fields are compared successfully with PIV data using the methodology of conditional averaging to take into account only the liquid phase characteristics as in PIV. The presence of two frequencies in a spectrum corresponding to the full and partial cavity detachments is analysed.

Study on the cavitation and noise characteristics by air injection in three dimensional hydrofoil

Study on the cavitation and noise characteristics by air injection in three dimensional hydrofoil

Three-dimensional Analysis of Two-way Fluid-structure Interaction on a Flexible Hydrofoil in Viscous Flow

Two-way Fluid-Structure Interaction of a three dimensional hydrofoil subjected to viscous flow at Re=750000 is investigated in this paper. A rectangular, cantilevered NACA66 hydrofoil is simulated using a finite element based CSD code, while the fluid flow is modeled with the incompressible, unsteady Reynolds Averaged Navier-Stokes equations using a finite volume based CFD code. The numerical computations are carried out through a strong coupling between these two separate solvers. The strongly coupled FSI solver is validated by comparing the present numerical results with experimental measurements in a water tunnel at the French Naval Academy. To quantify the FSI effects, rigid (stainless steel) and flexible (POM Poly-acetate) hydrofoils with the same undeformed geometry are simulated and compared.

Large eddy simulation of cavitation vortex interaction and pressure fluctuation around hydrofoil ALE 15

Numerical investigation on cavitating flow around a three dimensional hydrofoil ALE 15 is conducted by means of large eddy simulation. The calculated values of statistical average velocities agree well with the experimental data. Evolution of cavitation shows that the vortex structure and re-entrant jet in the vicinity of hydrofoil surface result in cavitation separation and shedding. The vorticity transport equation with vortex stretching term, vortex dilatation term, and baroclinic torque term is introduced to reveal the mechanism of cavitation-vortex interaction. Analysis results show that the cavitation-vortex interaction is mainly affected by the vortex stretching term and vortex dilatation term. The calculated pressure fluctuations on the hydrofoil shortest side show a pulse shift due to cavitation oscillation. The primary frequency of shedding cavitation is 307.14 Hz, which agrees well with the experimental data of 302 Hz.

Unsteady prediction of cavitating flow around a three dimensional hydrofoil by using a modified RNG k-ε model

The present paper suggests a modification of the turbulent viscosity model for predicting cavitating flows. It is to improve the two-equation turbulence model, which failed to accurately predict unsteady cloud cavitation due to the turbulent viscosity overestimated. The modification approach is that the cavitating flow depends on the turbulent viscosity in not only the mixture flow field but also the surrounding flow field in the vicinity of the vapor cavity. The turbulent viscosity in the standard RNG k-ε turbulence model was modified by the correlation between the cavitation model and the Barotropic equation of state. The unsteady cavitating flow around a 3-D NACA0015 hydrofoil was simulated by using the modified model as well as the standard model. The simulation result for the modified model agreed well with the experimental one. From the numerical result, the effect of the turbulent viscosity on the cavitation simulation and the cavitating flows was discussed. The present work showed that the strong turbulence is mainly produced in the condensation process, and it delays the cavitation inception in the next cycle.

Simulation of Water Wave Generated by Shallowly Submerged Asymmetric Hydrofoil

In this study the wave generated by flow around a shallowly submerged cambered hydrofoil near free surface is simulated numerically. The standard NACA 4412 hydrofoil section is used for ease of comparison with available experimental data. A commercial computational fluid dynamics (CFD) code FLUENT based on finite volume technique is used for the analysis of the two dimensional hydrofoil section. The k-ɛ turbulence model has been implemented to simulate turbulent flow past the foil in the free surface zone at different submergence ratios (h/c). To get the free surface elevation, ‘Volume of Fluid’ (VOF) method is incorporated in numerical simulation. To validate the computational results, the free surface wave generated by the flow around hydrofoil at submergence depth ratio h/c = 1 is compared with experimental results. The computed results show satisfactory agreement with the experimental measurements. Then free surface effects on wave profile are computed for six submergence depth ratios, h/c ranging from 1 to 5. Finally, the pressure coefficients at the trailing edge and hydrodynamic forces are computed at Fn=1, Re=3.11x 106 for different h/c ratios.

Computational Analyses of Cavitating Flows in Cryogenic Liquid Hydrogen

The objective of this study is to analyze the fundamental characteristics and the thermodynamic effects of cavitating flows in liquid hydrogen. For this purpose, numerical simulation of cavitating flows are conducted over a three dimensional hydrofoil in liquid hydrogen. Firstly, the efficiency of this computational methodology is validated through comparing the simulation results with the experimental measurements of pressure and temperature. Secondly, after analysing the cavitating flows in liquid hydrogen and water, the characteristics under cryogenic conditions are highlighted. The results show that the thermodynamic effects play a significant role in the cavity structure and the mass transfer, the dimensionless mass transfer rate of liquid hydrogen is much larger, and the peak value is about ninety times as high as water at room temperature. Furthermore, a parametric study of cavitating flows on hydrofoil is conducted by considering different cavitation number and dimensionless thermodynamic coefficient. The obtained results provide an insight into the thermodynamic effect on the cavitating flows.

Prediction of cryogenic cavitation around hydrofoil by an extensional Schnerr-Sauer cavitation model

Developing a robust computational strategy to address the rich physics characteristic involved in the thermodynamic effects on the cryogenic cavitation remains a challenging problem. The objective of this present study is to model the numerical methodology to simulate the cryogenic cavitation by implanting the thermodynamic effects to the Schnerr-Sauer cavitation model, and coupling the energy equation considered the latent heat. For this purpose, cavitating flows are investigated over a three dimensional hydrofoil in liquid hydrogen and nitrogen. Experimental measurements of pressure and temperature are utilized to validate the extensional Schnerr-Sauer cavitation model. Specifically, the further analysis of the cavitation solution with respect to the thermodynamic term is conducted. The results show that the extensional Schnerr-Sauer cavitation model predicts better accuracy to the quasi-steady cavitation over hydrofoil in the two cryogenic fluids.

Comparative Study on Viscous and Inviscid Analysis of Partial Cavitating Flow for Low Noise Propeller Design

선박용 프로펠러가 수중에서 빠른 속도로 회전할 때, 날개 표면의 국부적인 압력이 낮아짐에 따라 불가피하게 여러 형태의 공동이 발생한다. 이러한 공동현상은 근본적으로 날개 단면의 기하학적 형상 특성과 수동력학적 운용조건에 의해 결정되며, 결과적으로 선박 프로펠러에서 유기되는 수중방사소음은 공동의 발생특성과 직결된다고 할 수 있다. 따라서 저소음 프로펠러 설계를 위해서는 날개 단면의 형상에 따라 발생하는 공동과 그에 따른 소음특성을 이론 및 실험을 통해 정량적으로 평가할 수 있어야 한다. 본 연구에서는 저소음 프로펠러의 설계단계에서부터 적용이 가능한 부분공동성능 해석법 개발 및 날개단면 형상정보 도출을 목표로 선박용 프로펠러 날개 단면에서 발생하는 부분공동 다상 유동의 비점성 수치해석을 수행하였다. 또한 점성해석 상용프로그램인 FLUENT에서 제공하는 난류 및 공동 모델 조합에 따른 결과를 살펴보았으며, 점성 및 비점성 해석 결과를 비교, 평가 하였다. When a ship propeller having wing type sections rotates at high speed underwater, local pressure on the blade decreases and various types of the cavitation inevitably occur where the local pressure falls below the vapor pressure. Fundamentally characteristics of the cavitation are determined by the shapes of the blade section and their operating conditions. Underwater noise radiated from a ship propeller is directly connected to the occurrence of the cavitation. In order to design low noise propeller, it is preferentially demanded to figure out key features: how the cavity is generated, developed and collapsed and how the effect of viscosity works in the process. In this study, we first perform inviscid analysis of the partial cavity generated on two dimensional hydrofoil. Secondly, viscous analysis using FLUENT with different turbulence and cavitation models are presented. Results from both approaches are also compared and estimated.

J0501-4-3 RANS/LESハイブリッドモデルを用いたキャビテーション乱流の数値解析(流体機械の研究開発におけるEFD/CFD(4))

In this study, numerical simulation of turbulent cavitating flow around a two dimensional hydrofoil was performed. RANS/LES hybrid model were compared with RANS model. Dynamic switching according to flow field was used for RANS/LES hybrid model. In a non-cavitating and cavitating condition, time-averaged lift and drag coefficient obtained by both turbulence model were approximately the same magnitude. In a cavitating condition, the results obtained by both turbulence model showed periodic shedding of cloud cavitation. However, the Strouhal number obtained by RANS/LES hybrid model was smaller than that by RANS model, and was in the predicted range by an experiment.

Characteristic Analysis of Supercavitating Three Dimensional Hydrofoil between Parallel Walls

Characteristic Analysis of Supercavitating Three Dimensional Hydrofoil between Parallel Walls

Air Drawing and Flow Separation of a Shallowly Submerged Hydrofoil Section-2nd Report

In the 1 st paper, the author proposed the existence of the new type of flow separation due to air drawing, which can be found only for the purely two dimensional hydrofoil section and have not ever been fully noticed, and examined the essential properties, the condition for occurrence and scale effects etc.In the 2nd paper, the flow separation due to air drawing for the ogival sections of thickness chord ratio 3, 5, 7, 9 & 12%, which is superior to the aerofoil section of corresponding thickness chord ratio in flow separation characteristics, was observed in details in circulating flow tank. And, consequentely, two important factors, i, e critical submergence depth and critical approaching velocity was obtained for each ogival section of different thickness chord ratio. Finally, taking the critical Weber number measured for the flow separation due to air drawing into account, the charts were made for deciding whether the flow separation due to air drawing occurs or not.