Study On Aerodynamic Characteristics Of Mixer-diffuser With Bypass Flow

Mixer-diffuser with bypass flow is an important part for the turbojet/ramjet combined engine.It has the function of mixing mainstream and bypass flow,adjusting the velocity distribution at inlet of afterburner and liner.In this paper,three-dimensional numerical simulation and model experiments were carried out to investigate the effects of structural and aerodynamic parameters on flow field and aerodynamic performance of mixer-diffuser.The main conclusions are as follows.Fluent software were used to calculate and analyze the flow field and aerodynamic performances of the mixer-diffuser.The results show that velocity non-uniformity at inlet of the afterburner liner does not change with geometrical parameters monotonously.There is an optimum structural parameter to obtain a relative uniformity velocity at the inlet of the afterburner liner in the scope of this study.At the length of the baffle is 180 mm,the height of the baffle is 57.8mm,the diameter of bypass channel is 125 mm and the incidence angle of bypass flow is 45 degree,the velocity coefficient ranges from 0.81 to 1.18.With the decrease of the back pressure at afterburner liner exit or the increase of that at afterburner exit,the flowrate of the afterburner liner and total pressure recovery coefficient are all increased,while the velocity non-uniformity at inlet of the afterburner liner does not change obviously.With the increase of the total pressure of the bypass flow,the flowrate into the afterburner liner will increase significantly and the total pressure recovery coefficient decrease.When the total pressure of bypass flow decrease,the flowrate into afterburner liner between two adjacent bypass channels is very small and the velocity uniformity is poor.With inflow Mach number as Similarity Criterion for mixer-diffuser model experiments,an experimental system for the scaled mixer-diffuser was designed and built.And the aerodynamic performance of the mixer-diffuser under different bypass ratios and temperature ratios was tested.The experimental data show that the velocity coefficients at inlet of the afterburner liner basically keep symmetrical distribution centered on the bypass channel.The velocity coefficients are small in the middle and on both sides.When the bypass ratio is 0.317,the velocity uniformity at inlet of the afterburner liner is better than other bypass ratios.The velocity coefficient ranges from 0.69 to 1.17.When the temperature ratio is 2.33,the velocity uniformity at the inlet of the afterburner liner is poor.When the temperature ratio is 2,the velocity coefficient ranges from 0.791 to 1.123.The total pressure recovery coefficient does not change with the bypass ratio or temperature ratio obviously.