The Liutex core line method, first combined with the snapshot proper orthogonal decomposition (POD), is utilized in a supersonic micro-vortex generator (MVG) wake flow at Ma = 2.5 and Reθ = 5 760 to reveal the physic...The Liutex core line method, first combined with the snapshot proper orthogonal decomposition (POD), is utilized in a supersonic micro-vortex generator (MVG) wake flow at Ma = 2.5 and Reθ = 5 760 to reveal the physical significance of each POD mode of the flow field. Compared with other scalar-based vortex identification methods, the Liutex core line identification is verified to be the most appropriate approach that is threshold-free and provides full information of a fluid rotation motion. Meanwhile, the Liutex integration is employed to quantitatively track the evolution of the vortices in MVG wake and is applied to the determination of the effective control section of the MVG wake for the optimization study of MVG design. The physical mechanism of each POD mode for multi-scale and multi-frequency vortical structures is investigated by using Liutex core line identification to give some revelations. For the mean mode (mode 0) indicating the time-averaged velocity flowfield of the MVG wake flow, a pair of primary counter-rotating streamwise vortices and another pair of secondary vortices is uniquely identified by two pairs of Liutex core lines with Liutex magnitude. In contrast, mode 1 is featured by a fluctuated roll-up motion of streamwise vortex, and the streamwise component of the MVG wake is demonstrated to be dominant in terms of the total kinetic energy contribution. Meanwhile, a dominant shedding frequency of St = 0.072 is detected from the temporal behavior of mode 2, which has the organized arc-shaped vortex structures shedding from MVG induced by the K-H instability. Additionally, mode 4 subjects to low-frequency oscillations of the wall vortices and thus takes a relatively lower frequency of St = 0.044.展开更多
A high order implicit large eddy simulation (ILES) is carried out to study the mechanism of shock induced flow separation reduction under ramp-type MVG control. The mechanism was originally considered as that MVG can ...A high order implicit large eddy simulation (ILES) is carried out to study the mechanism of shock induced flow separation reduction under ramp-type MVG control. The mechanism was originally considered as that MVG can generate streamwise vortices which strongly mix boundary layer and the boundary layer becomes more capable to resist strong adverse pressure gradient caused by shock and to keep the boundary layer attached. However, according to our ILES, a chain of ring-like vortices is generated behind the ramp-type MVG and goes further to interact with the shock. When the ring-like vortices pass through the shock, the shock wave is weakened and altered while the vortex structures are quite stable. The instantaneous simulation shows that the spanwise ring-like vortex, not the streamwise vortex, plays a key role to weaken the shock and reduce the shock-induced separation. Detailed investigation on ring-like vortices and shock interaction will be given in this paper.展开更多
To investigate the characteristics of vaporized RP-3 kerosene combustion in a scramjet combustor enhanced by the micro vortex generator(MVG),a series of experiments are carried out based on the advanced combustion dia...To investigate the characteristics of vaporized RP-3 kerosene combustion in a scramjet combustor enhanced by the micro vortex generator(MVG),a series of experiments are carried out based on the advanced combustion diagnosis technique.The high-enthalpy incoming flow is accelerated to supersonic through a Mach 2.52 nozzle,the total pressure and temperature of which are 1.6 MPa and 1486 K,respectively.The effect of MVG on the ignition process,flame distribution,and combustor pressure along the bottom wall is well revealed,and the effects of the position and number of MVGs on stable combustion performance are analyzed.The results indicate that the development processes of the initial flame kernel with and without an MVG during ignition process show a similar behavior.The installation of an MVG can lift the shear layer,promote the penetration of flame deeper into the mainstream,and expand the area of the reactive region.Reducing the distance between the MVG and the injection position and increasing the number of MVGs are regarded as effective ways of improving the mixing degree of fuel and air with a resultant intensification of chemical reactions and flame luminescence.The effect of mixing and subsequent combustion is enhanced by shortening the distance between the MVG and the injection position.As the layout schemes of the MVG vary,the pressure distribution between the injection position and the leading edge of the cavity changes considerably,while that in the cavity remains almost constant.Increasing the number of MVGs is also beneficial for improving the premixed degree of fuel and incoming flow and results in more violent chemical reactions downstream of the cavity.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51906154).
文摘The Liutex core line method, first combined with the snapshot proper orthogonal decomposition (POD), is utilized in a supersonic micro-vortex generator (MVG) wake flow at Ma = 2.5 and Reθ = 5 760 to reveal the physical significance of each POD mode of the flow field. Compared with other scalar-based vortex identification methods, the Liutex core line identification is verified to be the most appropriate approach that is threshold-free and provides full information of a fluid rotation motion. Meanwhile, the Liutex integration is employed to quantitatively track the evolution of the vortices in MVG wake and is applied to the determination of the effective control section of the MVG wake for the optimization study of MVG design. The physical mechanism of each POD mode for multi-scale and multi-frequency vortical structures is investigated by using Liutex core line identification to give some revelations. For the mean mode (mode 0) indicating the time-averaged velocity flowfield of the MVG wake flow, a pair of primary counter-rotating streamwise vortices and another pair of secondary vortices is uniquely identified by two pairs of Liutex core lines with Liutex magnitude. In contrast, mode 1 is featured by a fluctuated roll-up motion of streamwise vortex, and the streamwise component of the MVG wake is demonstrated to be dominant in terms of the total kinetic energy contribution. Meanwhile, a dominant shedding frequency of St = 0.072 is detected from the temporal behavior of mode 2, which has the organized arc-shaped vortex structures shedding from MVG induced by the K-H instability. Additionally, mode 4 subjects to low-frequency oscillations of the wall vortices and thus takes a relatively lower frequency of St = 0.044.
基金supported by Air Force Office of Scientific Research (AFOSR) Grant FA9550-08-1-0201 supervised by Dr. John Schmisseur and then the Department of Mathematics at University of Texas at Arlington
文摘A high order implicit large eddy simulation (ILES) is carried out to study the mechanism of shock induced flow separation reduction under ramp-type MVG control. The mechanism was originally considered as that MVG can generate streamwise vortices which strongly mix boundary layer and the boundary layer becomes more capable to resist strong adverse pressure gradient caused by shock and to keep the boundary layer attached. However, according to our ILES, a chain of ring-like vortices is generated behind the ramp-type MVG and goes further to interact with the shock. When the ring-like vortices pass through the shock, the shock wave is weakened and altered while the vortex structures are quite stable. The instantaneous simulation shows that the spanwise ring-like vortex, not the streamwise vortex, plays a key role to weaken the shock and reduce the shock-induced separation. Detailed investigation on ring-like vortices and shock interaction will be given in this paper.
基金supported by the National Natural Science Foundation of China(No.12002373)。
文摘To investigate the characteristics of vaporized RP-3 kerosene combustion in a scramjet combustor enhanced by the micro vortex generator(MVG),a series of experiments are carried out based on the advanced combustion diagnosis technique.The high-enthalpy incoming flow is accelerated to supersonic through a Mach 2.52 nozzle,the total pressure and temperature of which are 1.6 MPa and 1486 K,respectively.The effect of MVG on the ignition process,flame distribution,and combustor pressure along the bottom wall is well revealed,and the effects of the position and number of MVGs on stable combustion performance are analyzed.The results indicate that the development processes of the initial flame kernel with and without an MVG during ignition process show a similar behavior.The installation of an MVG can lift the shear layer,promote the penetration of flame deeper into the mainstream,and expand the area of the reactive region.Reducing the distance between the MVG and the injection position and increasing the number of MVGs are regarded as effective ways of improving the mixing degree of fuel and air with a resultant intensification of chemical reactions and flame luminescence.The effect of mixing and subsequent combustion is enhanced by shortening the distance between the MVG and the injection position.As the layout schemes of the MVG vary,the pressure distribution between the injection position and the leading edge of the cavity changes considerably,while that in the cavity remains almost constant.Increasing the number of MVGs is also beneficial for improving the premixed degree of fuel and incoming flow and results in more violent chemical reactions downstream of the cavity.
