改进空化模型和修正湍流模型在螺旋桨空化模拟中的评估分析

为评估改进Sauer空化模型和修正切应力输运湍流模型联合使用时在螺旋桨空化模拟中的效果,以及"当σ>σi时,叶梢截面压力系数分布相对不再改变"的空化初生判定准则的适用性,以E779A螺旋桨为对象,对轻度(Ac/A0<0.1)、中度(0.1≤Ac/A0<0.25)和重度(0.25≤Ac/A0<0.5)空化程度下的桨叶空化形态、空化面积、叶截面压力系数分布、推力和力矩崩溃性能曲线以及初生空化数进行校验和分析。结果表明,在轻度空化下模拟空化面积较试验值略小;中度空化下与试验值吻合很好,模拟精度明显高于同类文献;在重度空化下因包含了泡空化面积而较试验值要大。在设计和非设计进速系数下,预报因空化引起的推力下降起始点均与试验值吻合很好,但推力衰减指数较试验值要大。应用空化初生判定准则得到J=0.77工况下初生空化数为3.25,较试验值仅偏差0.6%。由此表明,所采用的数值模型对于螺旋桨轻度和中度空化程度下的空化性能模拟具有较高的精度,所提出的空化初生判定准则是可信而且适用的。应用该准则,在求取0.88R(低侧斜桨)或0.7R(大侧斜桨)截面的初生空化数后,可较准确地预报螺旋桨空化斗图谱,进而预报舰艇空化初始航速。

Assessment of the Improved Cavitation Model and Modified Turbulence Model for Ship Propeller Cavitation Simulation

To assess the effectiveness of the adopted improved Sauer cavitation model and modified shear stress transport turbulence model for ship propeller cavitation simulation,and verify the applicability of the rule "when σ>σi,the pressure coefficient of the blade tip section is relative unaltered" to determine the cavitation inception,comprehensive validation and analysis of E779A propeller’s sheet cavitation pattern,cavity area,pressure coefficient distribution of the blade section,thrust and torque breakdown performance curves and its inception cavitation index are conducted under lightly,moderately and heavily cavitation levels.Results show that,under moderately cavitation level condition(0.1 ≤Ac/A0<0.25),simulated cavity area agrees very well the experiment and being better than that in opened research papers,while a little smaller than the test for the lightly cavitation level(Ac/A0<0.1) due to wall roughness effect,and over-prediction for heavily cavitation(0.25≤Ac/A0<0.5) because of the bubble cavitation area included.Under both of the design and un-design conditions,the predicted beginning points of thrust decline induced by cavitation are the same as experiment,while the slope indexes of thrust and torque are bigger.Under J=0.77 condition,the calculated cavitation inception number determined by the rule is 3.25 and just differs by 0.6% to its experiment.All the results above are concluded that the adopted numerical models are absolutely valuable for propeller cavitation simulation under moderately cavitation level associated with satisfactory results.Additionally,the inception rule is positively useful to determine the cavitaion inception and predict the inception bucket next after back inception index of the 0.88R section(for low skew angles) or 0.7R section(for highly-skewed propeller) being obtained.With this method,the critical inception speed prediction of warships is no more difficult.