A simple variable geometry scramjet inlet with a rotating cowl operating in a large Mach number range from 4 to 7 was designed.During the inlet design

one-dimensional flow theory was used to distribute the internal and external compressions.The inlet self-starting characteristics at Ma=4 and the global performance at different incoming Mach numbers were studied by means of numerical simulations.Results indicate:(1) Inlet's self-start can be realized successfully at Ma=4 under the help of the boundary layer diverter placed at the entrance of the cowl section.(2) Variable geometry inlet achieves a mass capture ratio of 70 percent at the starting Mach number

which is very favorable to the acceleration of the hypersonic vehicles.(3) Global performance parameters of the variable geometry inlet are greatly increased in the whole operating range compared with the fixed geometry inlet.(4) Position of the cowl rotation axis has a great effect on the inlet self-starting characteristic.