Simulation of Cavitating Flow around a 2-D Hydrofoil

In order to predict the effects of cavitation on a hydrofoil, the state equations of the cavitation model were combined with a linear viscous turbulent method for mixed fluids in the computational fluid dynamics (CFD) software FLUENT to simulate steady cavitating flow. At a fixed attack angle, pressure distributions and volume fractions of vapor at different cavitation numbers were simulated, and the results on foil sections agreed well with experimental data. In addition, at the various cavitation numbers, the vapor fractions at different attack angles were also predicted. The vapor region moved towards the front of the airfoil and the length of the cavity grew with increased attack angle. The results show that this method of applying FLUENT to simulate cavitation is reliable.

Investigation on cavitating turbulent flow for the twisted NACA66 hydrofoil using a PANS model with helicity modification

In the present paper,the unsteady cavitating turbulent flow over the twisted NACA66 hydrofoil is investigated based on an modified shear stress transfer k-ωpartially averaged Navier-Stokes(MSST PANS)model,i.e.,new MSST PANS(NMSST PANS)model,where the production term of kinetic energy in the turbulence model is modified with helicity.Compared with the experimental data,cavitation evolution and its characteristic frequency are satisfactorily predicted by the proposed NMSST PANS model.It is revealed that the interaction among the main flow,the reentrant jets,and sheet cavitation causes the formation of the primary shedding cavity near the mid-span and the secondary shedding cavity at each side of the twisted hydrofoil,and further induces the remarkable pressure gradient around shedding cavities.Along with the development of the primary and the secondary shedding cavities,the great pressure gradient associated with large cavity volume variation promotes the vortical flow generation and the spatial deformation of vortex structure during cavitation evolution,and results in the primary and the secondary U-type vortices.Further,dynamic mode decomposition(DMD)analysis is utilized to confirm the interaction among the main flow,the main reentrant jet and two side reentrant jets,and cavitation.These results indicate that the proposed NMSST PANS model is suitable to simulate the complicated cavitating turbulent flow for various engineering applications.

两种空化模型计算二维水翼空化流动研究

采用混合多相流模型和空化模型对攻角为6.5°的NACA66型二维水翼的空化流动进行数值研究.使用Singhal全空化模型(FCM)和Zwart-Gerber-Belamri(Z-G-B)空化模型,以实验数据为基准,对这两种空化模型得到的翼型表面压力分布系数和升、阻力系数以及流场结构进行了比较和分析,结果表明:FCM中,不凝结气体质量分数对计算结果影响较大,空化区长度随着不凝结气体质量分数的减小而变小;Z-G-B空化模型中,蒸发系数和凝结系数对结果有较大影响.总体说来,通过选取合理的经验系数,两种空化模型都给出了令人满意的空化流动结果.

改进Schnerr-Sauer模型在水翼空化模拟中的评估分析

为了提高Schnerr-Sauer模型模拟空化流动的能力,基于Rayleigh-Plesset方程和均相流假设建立了一种修正的Schnerr-Sauer空化模型,修正后的模型考虑了湍动能引起的脉动压力和不可凝结气体的影响。联立涡粘度系数修正的SST k-ω湍流模型,对绕二维Clark-Y翼型空化流进行了非定常数值计算,得到了时均化升阻力系数随空化数的变化曲线、云状空化时空泡周期性演变及其水平速度分布规律。通过与已有文献的实验结果对比分析得到,采用修正后的空化模型计算得到的时均化升阻力系数与实验值更为接近,并能较准确地捕捉升阻力系数随空化数的特殊变化规律;修正后的Schnerr-Sauer模型能准确地模拟翼型表面空化云的初生、成长、脱落和溃灭的全过程。本文的研究结果验证了修正后的Schnerr-Sauer模型在水翼空化流数值计算中的可靠性和准确性。

空泡半径非线性变化的空化模型及应用

为了提高Schnerr-Sauer空化模型模拟空化流动的能力,基于Rayleigh-Plesset方程和均相流假设建立了一种考虑空泡半径随时间非线性变化的空化模型.联立滤波器湍流模型,分别采用该非线性空化模型和原始Schnerr-Sauer模型对绕二维Clark-Y翼型空化流进行了非定常数值计算,得到了时均化升阻力系数随空化数的变化曲线、云空化时空泡周期性演变及其沿弦长方向速度分布规律.与其他的实验结果进行对比分析,结果表明:采用该非线性模型计算得到的时均化升阻力系数与实验值符合程度更好,并能较准确地捕捉升阻力系数在不同空化阶段的变化规律;该非线性模型能准确地模拟翼型尾缘空化云的成长、脱落和溃灭的全过程,且能更准确地模拟翼型尾流的速度场.

影响空化流数值计算的各种因素分析

通过CFD软件实现了二维翼型定常空泡流动的数值模拟,分析了空化模型、湍流模型和壁面函数法的选取对数值模拟计算结果的影响。对不同空化数条件下的空泡流场进行详细分析,得出了各种情况下翼型表面的压强分布曲线图。分析结果表明:几种空化模型均能够较好地模拟出空泡的起始、形成过程,与实验值相符合;但在空泡闭合区域,由于空化流的脉动特性,各空化模型之间的计算结果有所差别。RNGk-ε湍流模型和RSM湍流模型的计算结果比较一致,且与实验值吻合得较好;而标准k-ε模型的结果与实验值存在较大的偏差。采用增强壁面函数法的计算结果与实验值吻合得最好;而标准壁面函数法和非平衡壁面函数法的计算结果非常相近,但与实验值有一定的差距。