Investigation On Fuselage After-body Flow Separation Control By Spark Jet

As the fuselage after-body flow separation plays an important role in military transport aircraft,the application of fuselage after-body drag reduction technology is of great value to military transport aircraft.With the increasing demand for performance of military transport aircraft,the traditional passive fluid control technology could no longer meet the requirements.Nowadays,the spark jet,which is a new technology of fluid active control,has been applied in the research of fluid separation.Therefore,flow active control on fuselage after-body flow separation by the spark jet was numerically performed.The main contents and conclusions are as follows:1)There are bubble separation and vortex separation in fuselage after-body flow field.The bubble separation separates the high-speed mainstream from the low-speed viscous flow.The separation vortex grows from the edge of the after-body,diffuses and dissipates in the downstream.As the angle of attack decreases,the low pressure area on the edge of the after-body expands and lengthens,and the pressure coefficient decreases continuously.2)Ignoring the influence of the vortex separation,the spark jet is applied to the bubble separation control in two-dimensional fuselage.The influence of the location,energy,frequency and angle of incidence of spark jet was revealed by computational analysis.The effect of active control is better when the spark jet is lead into the boundary layer at the position of the separation point or the downstream of the separation point.When the spark jet is excited by larger energy,the separation control effect is better and the effect of drag reduction is worse.There is a control vacuum period in the low-frequency excitation.The total injection momentum of the jet in the high-frequency excitation is larger,so the effect of drag reduction is better.With the increase of jet incident angle,the separation control effect is weakened.According to the disadvantages of single spark jet,a scheme of three jet out-phase operation is proposed.Under the same total energy excitation,the effect of drag reduction of the new scheme is better than the single spark jet.Compared with the mass equivalent steady jet,pulsed jet,the pulsed jet has better performance on drag reduction than the steady jet.The spark jet is superior to the pulsed jet on drag reduction.3)The steady jet is used to verify the feasibility of the active jet control on three-dimensional fuselage after-body flow separation.Then,the influence of the energy,frequency and angle of incidence of spark jet on three-dimensional separation control and drag reduction was revealed by computational analysis.It is found that the effect of separation control of 30° incidence angle of spark jet is better,which restrains the bubble separation at the bottom and also affects the vortex separation and weakens the rotational speed of the vortex.When the excitation frequency is low,the jet has a control vacuum period.The higher the excitation frequency,the better the body drag reduction.The larger the energy excitation,the better the working performance of the synthetic jet,the better the effect of drag reduction,but the drag reduction range becomes smaller.Under the same total energy excitation,the scheme of high frequency with low energy is better than the scheme of low frequency with high energy.