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The dual-mode scramjet is a prime candidate for air-breathing propulsion engines given its broad speed range and high efficiency. The detailed structure of the pseudo-shock wave in the isolator is worth investigating. Therefore, the present study investigates the effect of isolator length on the pseudo-shock wave. We replicate the experimental work of the reference paper with a two-dimensional numerical model. Pressure distribution on the body surface is applied in the numerical validation. The numerical result is in good agreement with that of the existing experimental work. We simulate the thermal choking condition with a throttling device. As the throat area of throttling device decreases, the back pressure continues increasing and the pseudo-shock wave moves upstream. Avoiding unstart phenomenon is a key objective in the operation of dual-mode scramjet. Therefore, we investigate the critical condition shortly before unstart phenomenon occurs. The pseudo-shock wave structure is described by pressure distribution. Our main objective is to explore the effect of isolator length on the dual-mode scramjet. The optimal isolator length depends on the maximum back pressure and total pressure loss in the critical condition shortly before the unstart phenomenon occurs. The maximum back pressure in the critical condition is higher when the isolator length ranges from 8.7 to 20.7. The total pressure loss in the critical condition decreases at the beginning and then increases when the isolator length ranges from 8.7 to 20.7.

A numerical study on the asymmetric nozzle with a moving plate was conducted. The thrust vector control of the nozzle was investigated based on the transient phenomenon of a supersonic jet. The primary stream was exhausted from a convergent-divergent nozzle and deflected by the upper nozzle wall, which slid forward and backward according to certain motions. The transient flow behavior was numerically accessed by the unsteady Reynolds averaged Navier-Stokes equations coupled with a Reynolds stress turbulence model using a fully implicit finite volume scheme. Results of the primary numerical analysis were in good agreement with existing experimental data. The time-dependent system characteristics were specified in terms of vector angle, system thrust ratio and thrust loss.

In this paper, the effects of airfoils on the aerodynamic performance of small axial flow fans were investigated to reduce airflow turbulence on the blade surface and to improve the aerodynamic performance of small axial flow fans. Irregular airfoils where several convex grooves are bound in the blade pressure surface of the fans have two kinds. The wave-shaped edge is bound to the blade trailing edge of the fans and is designed from the smooth airfoil of the fans. The filtered N-S equations with the finite volume method and the standard k-ɛ turbulence model were adopted to carry out the steady simulation calculation. The large eddy simulation and the FH-W noise models were adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation are in good agreement with the tests, which proves that the numerical calculation method is feasible. The spectrum characteristics of aerodynamic noise of the smooth airfoil and the two kinds of irregular airfoils were analyzed. Although the fans of the three airfoils are regarded as noise sources, the vortex distribution features in the unsteady flow field are also described. Noise reduction mechanisms of the irregular designs of the airfoils were also discussed. The results of this research may provide proof of the parameter optimization and the structural design of small axial flow fans with low noise.