Experimental and numerical methods were utilized to investigate the back pressure effect on isolator flow characteristics by combustion or by flow choking. Combustion experiment with different hydrogen fuel equivalent ratios and wedge-blocked were conducted under the same airflow condition and the same isolator exit pressure ratio. Combustion and corresponding flow choking situations with different isolator exit pressures were investigated numerially to compare the flowfield details in the isolator under two situations. Experimental results indicate that when the shock train is about to enter the isolator

the same pressure distribution is achieved with these two choking methods; but when the isolator exit pressure ratio reaches 2.3

which means the shock train has entered the isolator

there is a significant difference between these two situations.Numerial result for these two situations suggest that separation zone for the combustion situation originally appears in the lower wall

but in the flow choking situation it appears in the upper wall

indicating that the shock train under combustion situation deflects upward and differs from that under the flow choking situation. When isolator exit pressure ratio reaches 3.0

the difference between two situations decreases

indicating that the difference may disappear eventually with the increasing back pressure. These results show that

only when the back pressure field by combustion and by flow choking experiment simulation is confirmed similar

flow choking experiment result can be used to assess the inlet unstart risk by back pressure.