【作者】 何朝晖；

【导师】 程永光； 季斌；

【作者基本信息】 武汉大学 ， 水利水电工程， 2022， 硕士

【摘要】 在经济全球化的新时代背景下,全球各国间的海运贸易日益频繁,现代船舶逐渐往大型化、高速化发展。螺旋桨运转时面临的不均匀船尾伴流变得更加剧烈,更容易产生非定常的空化现象。螺旋桨表面一旦发生空化,不但会降低螺旋桨的推力及工作效率,而且还会引起压力脉动的激增,进而产生较大的振动和噪声,严重危害了船舶运行的安全和稳定。如何在保证螺旋桨水动力性能的前提下,改善螺旋桨的空化性能,降低压力脉动一直以来是研究人员关注的热点问题。桨叶侧斜是影响螺旋桨空化的关键参数,对其影响规律和作用机理进行深入研究有着重大的工程意义。但是,有关侧斜参数的许多研究仍然局限在均匀流工况下的空化流动,且偏向于工程实际应用,简化了对流动机理的分析。为此,本文采用了数值模拟方法,使用E779A螺旋桨进行了数值计算方法验证,分析了空化的不利影响,并探究了空化引起压力脉动激增的影响机理,在此基础上,进一步建立了7个不同侧斜角度的螺旋桨,研究分析了均匀流及非均匀流中桨叶侧斜角度对螺旋桨的水动力性能、压力分布、空化性能、涡流场及压力脉动的影响,并对桨叶侧斜角度对空化、压力脉动的影响机理及规律展开了研究。本文的主要研究内容如下:(1)以E779A螺旋桨为研究对象,验证了本文数值计算方法的可靠性,研究了空化的发生对螺旋桨工作性能产生的一系列不利影响,并分析了空化对压力脉动的影响机理和作用规律。首先,以E779A螺旋桨为例,介绍了螺旋桨几何建模、结构化网格划分和边界条件设置等前处理过程;其次,通过对敞水性能、空化形态、非定常空化演变、压力脉动幅值的一阶叶频分量等进行数值模拟,验证了本文数值计算方法的可靠性;接着,对压力系数、涡流场及压力脉动等进行研究,结果表明空化的发生会降低螺旋桨的推力,增加湍流的不稳定性,并导致压力脉动的激增;最后,研究了压力脉动与非定常空化演变及空化体积导数等之间相互联系,结果表明非定常空化演变过程对压力脉动密切相关,空化体积二阶导是影响压力脉动的直接因素,这对于工程上抑制及消除压力脉动具有重要的意义。(2)在均匀流中,研究了桨叶侧斜角度对螺旋桨的敞水性能、压力分布、压力系数及空化形态的影响。对比了7个不同侧斜螺旋桨的推力系数、转矩系数及效率,发现侧斜角度为72°时,螺旋桨具有最大的推力和效率、较小的转矩,水动力性能最优;通过对压力分布及压力系数的研究,发现随着侧斜角度的逐渐增大,叶背导边处压力较低的区域逐渐趋于狭长,最低压力在逐渐升高,有利于抑制、推迟螺旋桨的空化;对空化形态的研究则表明,随着侧斜角度的逐渐增大,螺旋桨的空化逐渐由随边向导边收缩,空化区域逐渐变得狭长,梢涡空化变得更加明显。(3)在非均匀流中,研究了桨叶侧斜角度对螺旋桨非定常推力、非定常空化演变、涡流场及压力脉动的影响。对比了7个不同螺旋桨的非定常推力,发现侧斜角度的增加有助于降低非定常推力的振动范围,侧斜角度为72°时平均推力增加的最多;通过非定常空化及涡流场的分析,发现随着侧斜角度的增加,空化体积的变化逐渐变得平缓,但片空化下方的回射流得到加强,片空化更容易被“抬起”离开桨叶表面形成空化闭合区域;对压力脉动的研究则表明,桨叶侧斜角度的增加能够有效地抑制空化引起的压力脉动。随着侧斜角度的增加,压力脉动的峰值及幅值均在降低,压力脉动的变化范围也在逐渐减小。(4)研究分析了桨叶侧斜角度的增加对改善非定常空化演变、抑制压力脉动的影响机理及作用规律。选定了5个典型时刻,对比分析了瞬时压力脉动及对应的空化形态,结果表明:由于侧斜角度增大后,桨叶经过尾流区的时间变长,空化体积的变化趋于平缓,压力脉动得到抑制;此外,由于桨叶间空化的相互影响,侧斜角度较大的螺旋桨的空化体积变化及压力脉动将会得到抑制。之后,对比了7个不同侧斜角度螺旋桨的空化体积二阶导,结果表明侧斜角度的增加能够有效地降低空化体积二阶导的峰值及变化范围,从而进一步抑制螺旋桨的压力脉动。本文所做的工作加深了对空化引起船舶螺旋桨工作性能下降的认识和了解,揭示了空化引起压力脉动激增的作用机理,有助于工程上抑制空化引起的压力脉动。此外,本文研究了侧斜角度对螺旋桨水动力性能及空化性能的影响规律,并揭示了侧斜角度改善非定常空化演变及抑制压力脉动的作用机理,对工程上选取最优的桨叶侧斜角度具有参考价值。更多还原

【Abstract】 Under the background of the new era of economic globalization,maritime trade between countries in the world is becoming more and more frequent,and modern ships are gradually developing towards large-scale and high-speed.When the propeller is running,the uneven stern wake becomes more intense,which makes it easier to generate unsteady cavitation.Once cavitation occurs on the surface of the propeller,it will not only reduce the thrust and work efficiency of the propeller,but also lead to the surge of pressure fluctuation,which will cause vibration and noise and affect the safety and stability of ship operation.How to improve the cavitation performance of the propeller and reduce the pressure fluctuation on the premise of ensuring the hydrodynamic performance of the propeller has always been a hot issue for researchers.Blade skew is an important parameter affecting propeller cavitation,so it is of great engineering significance to study its action law and mechanism.However,many studies on the skew parameters are still limited to the cavitation flow under the condition of uniform inflow,and they are biased towards the practical engineering application,which simplifies the analysis of the flow mechanism.Therefore,based on the numerical simulation method,this paper uses the E779 A propeller to verify the numerical calculation method,analyzes the adverse effects of cavitation,and explores the influencing mechanism of the surge of pressure fluctuation caused by cavitation.On this basis,seven propellers with different skew angles are further established,and the effects of blade skew angles on the open water performance,pressure distribution,cavitation performance,vortex field and pressure fluctuation of propellers in uniform flow and non-uniform flow are studied and analyzed,and the influencing mechanism and rules of blade skew angles on cavitation and pressure fluctuation are also developed.The main contents of this paper are as follows:(1)Taking the E779 A propeller as the research object,the reliability of the numerical calculation method in this paper is verified,and a series of adverse effects of cavitation on the propeller performance are studied,and the influence mechanism and action law of cavitation on pressure fluctuation are analyzed.Firstly,taking the E779 A propeller as an example,the pretreatment processes such as geometric modeling,structured mesh generation and boundary condition setting of the propeller are introduced.Secondly,through numerical simulation of open water performance,cavitation shape,unsteady cavitation evolution and first-order blade frequency component of pressure fluctuation amplitude,the reliability of the numerical calculation method in this paper is verified.Then,the pressure coefficient,vortex field and pressure pulsation are studied.The results show that cavitation will reduce the thrust of propeller,increase the instability of turbulence and lead to the surge of pressure pulsation.Finally,the relationship between pressure pulsation,unsteady cavitation evolution and cavitation volume derivative is studied.The results show that the unsteady cavitation evolution process is closely related to pressure pulsation,and the second derivative of cavitation volume is the direct factor affecting pressure pulsation,which is of great significance for suppressing and eliminating pressure pulsation in engineering.(2)Under the uniform inflow,the influence of blade skew angle on the open water performance,pressure distribution,pressure coefficient and cavitation shape of the propeller is studied and analyzed.The thrust coefficient,torque coefficient and efficiency of seven different skew propellers are compared.It is found that when the skew angle is 72,the propeller has the maximum thrust and efficiency,smaller torque and the best hydrodynamic performance.Through the study of pressure distribution and pressure coefficient,it is found that with the increase of skew angle,the low pressure area at the leading edge of the blade back gradually becomes narrow and narrow,and the lowest pressure is gradually increasing,which is beneficial to restrain and delay the cavitation of the propeller.The study of cavity patterns shows that with the increase of skew angle,the cavitation of propeller gradually shrinks,the cavitation area gradually becomes narrow and narrow,and tip vortex cavitation becomes more obvious.(3)The research and analysis of the influence of blade skew angle on unsteady thrust,unsteady cavitation evolution,vortex field and pressure fluctuation of propeller are carried out.The unsteady thrust of seven different propellers is compared,and it is found that the increase of skew angle is helpful to reduce the vibration range of unsteady thrust,and the average thrust increases the most when the skew angle is 72.Through the analysis of unsteady cavitation and vortex field,it is found that with the increase of skew angle,the change of cavitation volume gradually becomes gentle,but the jet flow under the sheet cavitation is strengthened,and the sheet cavitation is easier to be "lifted" away from the blade surface to form a cavitation closed area.The study of pressure fluctuation shows that the increase of blade skew angle can effectively suppress the pressure fluctuation caused by cavitation.With the increase of skew angle,the peak value and amplitude of pressure fluctuation are decreasing,and the range of pressure fluctuation is also gradually decreasing.(4)The influence mechanism and action rule of increasing blade skew angle on unsteady cavitation evolution and pressure fluctuation are studied and analyzed.Five typical moments were selected,and the instantaneous pressure fluctuation and the corresponding cavity patterns were compared and analyzed.The results showed that with the increase of the skew angle,the time for the blade to pass through the wake region became longer,the change of cavitation volume tended to be gentle,and the pressure fluctuation was suppressed.In addition,due to the interaction of cavitation between blades,the change of cavitation volume and pressure fluctuation of propeller with large skew angle will be suppressed.Then,the second derivative of cavitation volume of seven propellers with different skew angles is compared.The results show that the increase of skew angle can effectively reduce the peak value and variation range of the second derivative of cavitation volume,thus further suppressing the pressure fluctuation of propellers.The work done in this paper has deepened the knowledge and understanding of the performance degradation of marine propellers caused by cavitation,revealed the mechanism of pressure pulsation surge caused by cavitation,and contributed to the suppression of pressure pulsation caused by cavitation in engineering.In addition,this paper studies the influence law of the skew angle on the hydrodynamic performance and cavitation performance of the propeller,and reveals the mechanism of the skew angle to improve the unsteady cavitation evolution and suppress the pressure pulsation,which has reference value for selecting the optimal blade skew angle in engineering.更多还原