The exergy-based multidisciplinary optimization (MDO) method has been applied to conceptual design of a scramjet engine by analyzing the available energy in each subsystem within a highly integrated and high efficiency required vehicle. Regarding the conceptual design of a scramjet, the stream thrust method has been adopted to calculate each subsystem's in/out area, i.e., inlet, isolator, combustor and nozzle. Next, a newly developed evaluation program was utilized to evaluate the performance of the vehicle's internal flow. With the calculated state parameters obtained from the evaluation program results, the exergy analysis was then performed. Subsequently, genetic algorithm and non-dominated sorting genetic algorithm were used to optimize the design variables. The maximum exergy efficiency was measured and the specific impulse (I sp) optimization was conducted separately, and a multi-objective optimization containing both was also investigated. The results demonstrated that the optimization objective with exergy efficiency was suitable for long-endurance vehicles and high-efficiency fuel utilization, the maximum I sp was suitable for high acceleration and high thrust, and the Pareto front could address both needs. It was also found that the cycle static temperature ratio and static pressure ratio of the nozzle should be specifically set at an optimized value to obtain the maximum exergy efficiency and I sp .

Three-dimensional supersonic nozzle is an important component of air-breathing hypersonic vehicles to produce thrust and lift force. Since the length of nozzle with ideal design is too long to meet the trim requirements of integrated airbreathing hypersonic vehicles, it is necessary to design a truncated nozzle to provide excellent aerodynamic performance. In the present study, an axisymmetric minimum length nozzle was firstly designed using method of characteristics. Then, streamlines trace technique with an offset circular entrance was adopted to extract the three-dimensional asymmetric nozzle. Nonlinear compression method was applied to compress the nozzle to a suitable length. Afterward, a surrogate-based optimization of three design variables, namely pressure ratio of nozzle's exhaust to ambient, reserved initial expansion ratio, and average compression ratio was performed with the objectives of thrust and lift force, and a Pareto optimal front was therefore obtained. Numerical simulations were also made at six selected Pareto front cases to offer an insight into the flow fields. An infection point was observed in the Pareto front due to the maximum constrained length. The pressure ratio was found to be the most influential parameter, and the middle parts of Pareto front revealed better uniformity of exit flow.

For this paper, an investigation into the differences in the aerodynamic performance of fans caused by installation heights was conducted using computational fluid simulation. The predictions presented in this paper are in great agreement with the experimental data. The results show that a vortex is observable on the side of the motor, as it first accelerates and then obviously decelerates while passing through the impeller inlet to the front of the blade passage. Higher motor installation heights result in a decrease in static pressure and static pressure efficiency at higher flow rates. At the maximum flow rate, the static pressure efficiency of the fan at a lower installation height increased by 10% with the original fan, and the static pressure coefficient increased by 23% as well. The results reported in this paper demonstrate that installation heights greatly affect the aerodynamic performance of an isolated centrifugal fan under higher flow rate conditions and that the range of fan operation is extended at reasonable heights.