A numerical study has been carried out to investigate the full flow path and aerodynamic characteristics of a hypersonic vehicle at a 7.0 free stream Mach number. Results indicate that the inlet started and unstarted ...A numerical study has been carried out to investigate the full flow path and aerodynamic characteristics of a hypersonic vehicle at a 7.0 free stream Mach number. Results indicate that the inlet started and unstarted operations have remarkable effects on the flow pattern of the full flow path. When the inlet operates in a started mode, the transverse pressure gradient generated by the forebody alters the air captured characteristics and the entering flow quality of the inlet. Furthermore, the expansion process of the nozzle jet flow is obviously affected by the external flow field around the afterbody with the cross section shape transiting from a near rectangle at the exit of the nozzle to a near triangle at the tail of the vehicle. When the inlet operates in an unstarted mode, the aerodynamic instability can be observed in the full flow path of the vehicle. Due to the oscillation of the external compressed shock wave and nozzle jet flow, the aerodynamic characteristics of the vehicle vary periodically with the lift-drag ratio changing from 0.25 to 2.09. Finally, by comparing to the experimental data, the reliability of the CFD is verified.展开更多
Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a fr...Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow features.Results indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two facilities.Tripped cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.展开更多
In this paper,a model reference adaptive control(MRAC)augmentation method of a linear controller is proposed for air-breathing hypersonic vehicle(AHV)during inlet unstart.With the development of hypersonic flight tech...In this paper,a model reference adaptive control(MRAC)augmentation method of a linear controller is proposed for air-breathing hypersonic vehicle(AHV)during inlet unstart.With the development of hypersonic flight technology,hypersonic vehicles have been gradually moving to the stage of weaponization.During the maneuvers,changes of attitude,Mach number and the back pressure can cause the inlet unstart phenomenon of scramjet.Inlet unstart causes significant changes in the aerodynamics of AHV,which may lead to deterioration of the tracking performance or instability of the control system.Therefore,we firstly establish the model of hypersonic vehicle considering inlet unstart,in which the changes of aerodynamics caused by inlet unstart is described as nonlinear uncertainty.Then,an MRAC augmentation method of a linear controller is proposed and the radial basis function(RBF)neural network is used to schedule the adaptive parameters of MRAC.Furthermore,the Lyapunov function is constructed to prove the stability of the proposed method.Finally,numerical simulations show that compared with the linear control method,the proposed method can stabilize the attitude of the hypersonic vehicle more quickly after the inlet unstart,which provides favorable conditions for inlet restart,thus verifying the effectiveness of the augmentation method proposed in the paper.展开更多
A wavecatcher type scramjet intake,that reduces the Mach number number from 4 to 1.552,is used as the basis for a study of flow starting/unstarting as affected by freestream angles of attack and sideslip.The intake de...A wavecatcher type scramjet intake,that reduces the Mach number number from 4 to 1.552,is used as the basis for a study of flow starting/unstarting as affected by freestream angles of attack and sideslip.The intake design is based on a morphed streamtube consisting of two conical flow streamlines using streamline tracing and osculating axisymmetric design theory.Intake flow and performance is modeled using the numerical CFD code and the k-e turbulence model.The intake unstarts at a sideslip angle of 2,a positive angle of attack of 1.Both positive angle of attack and sideslip angle have an adverse effect on the startability of the MBus intake.At negative angles,the intake initially unstarts at5angle of attack,due to the thickened shear layer induced by the streamwise vortex.Then it re-starts at8angle of attack,mainly due to the expansion fan formed at the leading edge,causing the shock wave structures inside the intake to be reestablished.展开更多
The variable geometry supersonic inlet tends to decrease the throat area to reduce the Mach number upstream of the terminal shock,so as to reduce the flow loss.However,excessive Internal Contraction Ratio(ICR)exposes ...The variable geometry supersonic inlet tends to decrease the throat area to reduce the Mach number upstream of the terminal shock,so as to reduce the flow loss.However,excessive Internal Contraction Ratio(ICR)exposes the inlet to a greater risk of unstart,which inevitably results in a process of increasing the throat area to aid the inlet restart.In the above throat regulation process,the inlet undergoes the start,unstart,and restart states in turn.In order to reveal the flow structure and mechanism of this process,a two-dimensional unsteady numerical simulation combined with a dynamic mesh technique were employed.The shock-on-lip Mach number of the studied inlet is 4.0 and the flight angle of attack is+6°.Analysis was focused on the state with a freestream Mach number of 3.0.The results clearly show that the flow response hysteresis appears,and restart is only realized when the throat area is obviously increased as compared to that of unstart due to the historical unstart flow structure.In addition,three typical flow fields were analyzed,and it is found that the separation ahead of the inlet was the key factor affecting the hysteresis.Finally,unstart and restart boundaries of the inlet were discussed,and the factors influencing its deviation from the typical boundaries of dual-solution area were analyzed.The newly predicted unstart and restart boundaries are much closer to the CFD results.展开更多
基金National Nature Science Foundation of China (5060601)
文摘A numerical study has been carried out to investigate the full flow path and aerodynamic characteristics of a hypersonic vehicle at a 7.0 free stream Mach number. Results indicate that the inlet started and unstarted operations have remarkable effects on the flow pattern of the full flow path. When the inlet operates in a started mode, the transverse pressure gradient generated by the forebody alters the air captured characteristics and the entering flow quality of the inlet. Furthermore, the expansion process of the nozzle jet flow is obviously affected by the external flow field around the afterbody with the cross section shape transiting from a near rectangle at the exit of the nozzle to a near triangle at the tail of the vehicle. When the inlet operates in an unstarted mode, the aerodynamic instability can be observed in the full flow path of the vehicle. Due to the oscillation of the external compressed shock wave and nozzle jet flow, the aerodynamic characteristics of the vehicle vary periodically with the lift-drag ratio changing from 0.25 to 2.09. Finally, by comparing to the experimental data, the reliability of the CFD is verified.
基金co-supported by the China Postdoctoral Science Foundation (No. 2017M612059)the Fundamental Research Funds for the Central Universities of China (JZ2015HGBZ0471)the National Natural Science Foundation of China (Nos. 11402263 and 11132010)
文摘Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow features.Results indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two facilities.Tripped cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.
基金supported by the Foundation of Shanghai Aerospace Science and Technology(SAST2016077)。
文摘In this paper,a model reference adaptive control(MRAC)augmentation method of a linear controller is proposed for air-breathing hypersonic vehicle(AHV)during inlet unstart.With the development of hypersonic flight technology,hypersonic vehicles have been gradually moving to the stage of weaponization.During the maneuvers,changes of attitude,Mach number and the back pressure can cause the inlet unstart phenomenon of scramjet.Inlet unstart causes significant changes in the aerodynamics of AHV,which may lead to deterioration of the tracking performance or instability of the control system.Therefore,we firstly establish the model of hypersonic vehicle considering inlet unstart,in which the changes of aerodynamics caused by inlet unstart is described as nonlinear uncertainty.Then,an MRAC augmentation method of a linear controller is proposed and the radial basis function(RBF)neural network is used to schedule the adaptive parameters of MRAC.Furthermore,the Lyapunov function is constructed to prove the stability of the proposed method.Finally,numerical simulations show that compared with the linear control method,the proposed method can stabilize the attitude of the hypersonic vehicle more quickly after the inlet unstart,which provides favorable conditions for inlet restart,thus verifying the effectiveness of the augmentation method proposed in the paper.
基金National Natural Science Foundation of China(No.:12002261)National Postdoctoral Program for Innovative Talents of China(No.:BX20200267)+2 种基金Young Talent fund of University Association for Science and Technology in Shaanxi of China(No.:20200501)China Postdoctoral Science Foundation(No.:2020M673411)the Fundamental Research Funds for the Central Universities of China(No.:xzy012020096).G.Chen are grateful for the support of National Natural Science Foundation of China(No.:11872293).
文摘A wavecatcher type scramjet intake,that reduces the Mach number number from 4 to 1.552,is used as the basis for a study of flow starting/unstarting as affected by freestream angles of attack and sideslip.The intake design is based on a morphed streamtube consisting of two conical flow streamlines using streamline tracing and osculating axisymmetric design theory.Intake flow and performance is modeled using the numerical CFD code and the k-e turbulence model.The intake unstarts at a sideslip angle of 2,a positive angle of attack of 1.Both positive angle of attack and sideslip angle have an adverse effect on the startability of the MBus intake.At negative angles,the intake initially unstarts at5angle of attack,due to the thickened shear layer induced by the streamwise vortex.Then it re-starts at8angle of attack,mainly due to the expansion fan formed at the leading edge,causing the shock wave structures inside the intake to be reestablished.
基金co-supported by the National Natural Science Foundation of China(Nos.U20A2070,12025202,11772156,51806102,and 51906104)。
文摘The variable geometry supersonic inlet tends to decrease the throat area to reduce the Mach number upstream of the terminal shock,so as to reduce the flow loss.However,excessive Internal Contraction Ratio(ICR)exposes the inlet to a greater risk of unstart,which inevitably results in a process of increasing the throat area to aid the inlet restart.In the above throat regulation process,the inlet undergoes the start,unstart,and restart states in turn.In order to reveal the flow structure and mechanism of this process,a two-dimensional unsteady numerical simulation combined with a dynamic mesh technique were employed.The shock-on-lip Mach number of the studied inlet is 4.0 and the flight angle of attack is+6°.Analysis was focused on the state with a freestream Mach number of 3.0.The results clearly show that the flow response hysteresis appears,and restart is only realized when the throat area is obviously increased as compared to that of unstart due to the historical unstart flow structure.In addition,three typical flow fields were analyzed,and it is found that the separation ahead of the inlet was the key factor affecting the hysteresis.Finally,unstart and restart boundaries of the inlet were discussed,and the factors influencing its deviation from the typical boundaries of dual-solution area were analyzed.The newly predicted unstart and restart boundaries are much closer to the CFD results.
