Research On The Unsteady Flow Phenomenon Of Isolator Under Complex Inlet And Outlet Conditions

Isolator is an important part of scramjet.Under the real flowing conditions,there will be a vibration of shock trains in the isolator even if the boundary conditions of isolator are steady.But how this phenomenon is formed is unclear.So,the author researches the unsteady flow phenomenon of isolator under complex inlet and outlet conditions.Firstly,we research a computational model fitting well with the unsteady flow computation,and contrast it with the traditional model with a real inlet before the isolator.The result shows the difference of frequency between these two models is 0.01%,and the difference of amplitude is 4.13%.Basing on this,the impact of the pressure relief slot and the way of how the back pressure is added to the unsteady phenomenon is studied.Thus,we conclude a computational model fitting best with the unsteady flowing phenomenon in the isolator.Secondly,the impact of the incident shock waves,including the Mach number of the inlet of isolator and the lip length to the unsteady flowing phenomenon are studied.The frequency of the shock train vibration will get larger with the angle of cowl.With the change of the angle of cowl,the form of the shock train vibration changes randomly.For the vibration owing only one frequencies,the frequency of vibration of each measuring point is the same,but comparing to the outlet of isolator,the amplitude of vibration of the measuring point in the first shock in the shock train increases 71.9%.For the vibration constructed by multiple frequencies,comparing to the outlet of isolator,the amplitude ratio between the 1st order and 2nd order of the measuring point in the first shock in the shock train increases 4.49 times,well the ratio of 1st and 3rd order increases 5.08 times.Mean-well,the frequency of 1st order vibration gets closer to the frequency of the whole shock train vibration.With the increasing of Mach number of the inlet of isolator,the shock train will change to resistant vibration,finally the isolator will occurs steady flowing phenomenon.During this period the amplitude of equal amplitude vibration will increase.The position of the incidence of the cowl wall shock will the length of lip.When this is position is getting father to the inlet of the isolator,the phenomenon of shock train will get apparent.Finally,we take up an experiment based on the 3-D rotundity isolator.The impact of the Mach number of the inlet of isolator,the undistributed degree of the inlet of the isolator and the back pressure to the unsteady flowing phenomenon are studied.For the isolator length and diameter ratio7.6 uniformity flow model,the frequency is 610 Hz of Mach number 6 while 585 Hz of Mach number5,but the amplitude will decreasing 50%.,which is similar to the result of numeral computation.For the isolator length and diameter ratio 13 under the condition of Mach number 5 and 6,the frequency will both increase 5% and the amplitude of vibration will increase nearly 100%.For the model of Mach number 6,with the increasing of back pressure,the frequency of vibration still remains 610 Hz,but the amplitude of vibration will increase 3 times.