Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numer...Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numerical simulations,the shear layer deformation and pressure increase in the cavities due to the impingement of the door-leading-edge shocks are identified via comparison with those in the cavity without doors.As the door-opening angle decreases from 90°,the shear layer above the forepart of the cavity is gradually raised by the high pressure in the cavity.When the door-opening angle decreases to 30°and 15°,the boundary layer on the upstream flat plate of the cavity separates,and separation shock is observed.The doors enhance the instability of the cavity flow and increase the pressure fluctuations in the cavities.A new oscillation pattern,referred to as coupled oscillation,is observed in the cases with separation on the upstream flat plate,in which the separation shock oscillates at the same dominant frequency as the flow inside the cavity.Compared with the cavity without doors,this coupled oscillation causes a lower oscillation frequency and a larger overall sound pressure level.Cross-correlation analyses between pressure signals indicate that the disturbances generated at the trailing edge of the cavity can propagate to the separation on the upstream flat plate and cause coupled oscillation of the separation shock.The fundamental frequencies of the coupled oscillations can be normalized to approximately the same Strouhal number as that of the cavity without doors.These findings support that the oscillation mechanisms of hypersonic cavities without and with doors are primarily dominated by acoustic feedback.展开更多
超空泡技术对水下航行体减阻增程具有重要意义。航行体近水底面航行时,刚性壁面会对航行体的空泡形态产生显著影响,从而影响航行体的运动姿态和稳定性。为研究壁面效应对超空泡航行体空化的影响,采用VOF(volume of fluid)多相流模型、Sc...超空泡技术对水下航行体减阻增程具有重要意义。航行体近水底面航行时,刚性壁面会对航行体的空泡形态产生显著影响,从而影响航行体的运动姿态和稳定性。为研究壁面效应对超空泡航行体空化的影响,采用VOF(volume of fluid)多相流模型、Schnerr-Sauer空化模型和Realizable k-ε湍流模型,分别对单壁面作用以及壁面边界层作用下的超空泡航行体进行模拟研究,以揭示壁面、剪切层与超空泡航行体的耦合作用机理。结果表明:对于单壁面作用,由于刚性壁面对空泡膨胀排挤水体的阻碍效应,近壁面侧的空泡显著减小,远壁面侧的空泡略微增大,超空泡向远壁面侧偏斜,并且航行体离壁面越近,超空泡的偏斜越强,甚至还会使得航行体下侧沾湿。然而,在壁面边界层作用下,由于航行体上侧绕流快于下侧,周围流线向低速的近壁面侧偏斜,空泡上凸下平的不对称性减弱。随着边界层厚度增加以及航行体与壁面距离减小,航行体周围的剪切作用增强,超空泡从向远壁面侧偏斜逐渐转变为向近壁面侧偏斜,最终变成上平下凸的不对称形态。展开更多
基金supported by the National Natural Science Foundation of China(Nos.12172354,12388101,U21B6003)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB0620201).
文摘Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numerical simulations,the shear layer deformation and pressure increase in the cavities due to the impingement of the door-leading-edge shocks are identified via comparison with those in the cavity without doors.As the door-opening angle decreases from 90°,the shear layer above the forepart of the cavity is gradually raised by the high pressure in the cavity.When the door-opening angle decreases to 30°and 15°,the boundary layer on the upstream flat plate of the cavity separates,and separation shock is observed.The doors enhance the instability of the cavity flow and increase the pressure fluctuations in the cavities.A new oscillation pattern,referred to as coupled oscillation,is observed in the cases with separation on the upstream flat plate,in which the separation shock oscillates at the same dominant frequency as the flow inside the cavity.Compared with the cavity without doors,this coupled oscillation causes a lower oscillation frequency and a larger overall sound pressure level.Cross-correlation analyses between pressure signals indicate that the disturbances generated at the trailing edge of the cavity can propagate to the separation on the upstream flat plate and cause coupled oscillation of the separation shock.The fundamental frequencies of the coupled oscillations can be normalized to approximately the same Strouhal number as that of the cavity without doors.These findings support that the oscillation mechanisms of hypersonic cavities without and with doors are primarily dominated by acoustic feedback.
文摘超空泡技术对水下航行体减阻增程具有重要意义。航行体近水底面航行时,刚性壁面会对航行体的空泡形态产生显著影响,从而影响航行体的运动姿态和稳定性。为研究壁面效应对超空泡航行体空化的影响,采用VOF(volume of fluid)多相流模型、Schnerr-Sauer空化模型和Realizable k-ε湍流模型,分别对单壁面作用以及壁面边界层作用下的超空泡航行体进行模拟研究,以揭示壁面、剪切层与超空泡航行体的耦合作用机理。结果表明:对于单壁面作用,由于刚性壁面对空泡膨胀排挤水体的阻碍效应,近壁面侧的空泡显著减小,远壁面侧的空泡略微增大,超空泡向远壁面侧偏斜,并且航行体离壁面越近,超空泡的偏斜越强,甚至还会使得航行体下侧沾湿。然而,在壁面边界层作用下,由于航行体上侧绕流快于下侧,周围流线向低速的近壁面侧偏斜,空泡上凸下平的不对称性减弱。随着边界层厚度增加以及航行体与壁面距离减小,航行体周围的剪切作用增强,超空泡从向远壁面侧偏斜逐渐转变为向近壁面侧偏斜,最终变成上平下凸的不对称形态。
