前缘空化对弹性水翼振动特性影响数值模拟

Numerical simulations of the effect of leading edge cavitation on the vibration characteristics of an elastic hydrofoil

水力机械偏离设计工况运行时,前缘空化将显著改变流场,进而改变流场与叶片结构之间的流固耦合效应,导致叶片振动特性发生改变。该文以NACA0009弹性水翼为研究对象,采用基于剪应力输运(SST)k-ω湍流模型和Zwart-Gerber-Belamri(ZGB)空化模型的三维Reynold平均数值模拟方法预测流场特性,利用分离式双向迭代的流固耦合方法计算空化条件下水翼的预设激振响应,获得了弹性水翼水中固有频率与附加阻尼比。通过实验数据验证了数值计算结果的可靠性。计算结果表明:随着空化数的降低,水翼前缘空化长度、厚度和边界层厚度均增大。随着空化区域长度的增加,水翼尾部脱落涡频率降低。空化系数变化对弯曲振动振型影响较小,但对扭转振动振型的影响较大。随着前缘空化区域的增大,弹性水翼弯曲模态与扭转模态的固有频率变化趋势一致,但附加阻尼比的变化依赖于振型。当弹性水翼在攻角2°、流速14 m/s的工况运行时,前缘空化出现后,弯曲振型下固有频率的最大增幅为2.25%,附加阻尼比减小9.00%,扭转振型下固有频率的最大增幅为20.12%,附加阻尼比增大165.70%。

When hydraulic machinery operating conditions differ from the design conditions,leading edge cavitation can significantly disrupt the flow field and increase fluid-solid interactions(FSI)between the flow and the blade which change the system vibration characteristics.The flow around a NACA0009 elastic hydrofoil was simulated using the shear stress transfer(SST)turbulence model and the Zwart-Gerber-Belamri(ZGB)cavitation model in the three dimensional Reynolds average numerical simulation(RANS)method.The damped natural frequency and the added damping ratio were then calculated using a two-way FSI numerical method.The results were verified against existing experimental data.The computational results show that both the length and thickness of the cavitation region expand and the boundary layer on the hydrofoil leading edge grows thicker as the cavitation number decreases.The increasing cavitation length then reduces the shedding vortex frequency from the hydrofoil trailing edge.The leading edge cavity has little influence on the vibration shape of the bending mode,but greatly influences the vibration shape of the torsional mode.Enlarging the cavitation region increases the natural frequencies of the bending and torsional modes of the elastic hydrofoil in the same way,while the effects of the added damping ratio depend on the vibration mode.At an attack angle of 2°and a flow rate of 14 m/s,the natural frequency of the hydrofoil in the bending mode with leading edge cavitation increases up to 2.25%and the added damping ratio decreases by 9.00%,while the natural frequency in the torsional mode increases by 20.12%and the added damping ratio increases by 165.70%.