非定常キャビテーション流れの流動刺激が促進する溶存気体の析出に関する一考察

抄録

It was shown in the past bench-mark simulation of cavitation that a lift of hydrofoil is underestimated in the break-down region in the condition of transient cavitation at high angle of attack in which cavitation has highly unsteady behavior. The authors assume that one of the reasons of the underestimation is lack of consideration of liberation of dissolved non-condensable gas and assuming the threshold of cavitation appearance at saturated vapor pressure in all the conventional numerical method of cavitation. In the present experiment of cavitation tunnel, it was shown that the liberation amount of dissolved oxygen is larger in unsteady cavitating flow than in quasi-steady cavitating flow although the cavity volumes are almost same. The experimental result gives a reason on the assumption and indicates that the dynamic stimulation with unsteady cavitating flow causes the liberation of non-condensable gas. In the numerical simulation of cavitation, the dynamic stimulation was modeled by turbulent energy, Reynolds stress, production term and baroclinic torque, respectively. The liberation models were applied for homogeneous numerical method of vaporous cavitation, then the threshold value of appearance of cavitation changes according to the local flow field. In the numerical result, it was shown that the underestimation of lift was partially improved by considering liberation of non-condensable gas by the dynamic stimulation of baroclinic torque in the unsteady cavitating flow.