Study On Hysteresis Phenomenon Caused By Back Pressure In Curved Isolator

The isolator is a key component of the scramjet engine.The isolator includes three functions: The first one is to pressurize the inlet flow,the second one is to prevent the back pressure from influencing the inlet,the third one is to act as the connect between inlet and combustion chamber.When the position of inlet and combustion chamber are not in the same line,curved isolator becomes a necessity.So,the study on the curved isolator is important and valuable.Experiment and CFD are carried out to deeply study on hysteresis phenomenon caused by back pressure in curved isolator.Numerically,the software Fluent was used to simulate the internal flow field isolator,and some important parameters were obtained.A typical isolator composed by two tangential arcs was designed,and some experimental methods were taken to focus on the phenomenon.For example,schlieren,pressure senor and so on.Firstly,aiming at the process how the structure of shock train evolves in the curved isolator when the back pressure changes,a great deal of simulation are conducted.Though analyzing the flow field structure in the different back pressure,the hysteresis phenomenon can be obtained.The position of first separation zone of shock train in the curved isolator was found by the UDF of software.It shows that the shock train in the isolator is unsteady,and it reflects how the shock train moves in the isolator.By analyzing the results,it can be concluded that the three-dimension effect is very strong,and it effects the hysteresis phenomenon.Secondly,based on schlieren pictures and the pressure distribution along the wall,the hysteresis phenomenon can be validated again.The schlieren pictures shows the evolvement process of shock train in the isolator,the pressure of certain point shows the unsteady property and self-oscillation.The relationship between self-oscillation and the position of shock train was concerned.In order to prove the hysteresis phenomenon exists only in curved isolator,the same experiment was also conducted in the straight isolator,and the hysteresis phenomenon was not found in the straight isolator which was designed in this paper.Thirdly,the straight isolator with inlet and broken line isolator were also concerned in this paper,and the hysteresis phenomenon was also found in these two isolator.These two isolators have the similar to the curved isolator.The performance of isolator effected by hysteresis phenomenon was also taken into account.Last,the reason why the hysteresis phenomenon exists in the curved was considered in the paper.There are two reasons,one is the original pressure distribution along the wall and the original structure in the curved isolator may lead to the phenomenon.The other is that the hysteresis phenomenon also exists when the separation zone seperates and combines.There are compression wave and expansion wave in the isolator by turns,and the typical pressure distribution is “decrease-increase”,Tis kind of structure may cause hysteresis.And the separation zone in the shock train is easy to combine with the nearby separation zone to become a bigger one.But the bigger one is hard to separate.