Volume 32, Issue 3 -

To obtain motion characteristics of the lubricating oil film on the aero-engine bearing chamber wall, a complete mathematical model based on theoretical study to solve three-dimensional unsteady oil film motion was established. On the basis of verifying the rationality of the computational model, the variations of the oil film thickness, velocity and temperature with the rotation speed and lubricating oil flow were analyzed and studied. The numerical results show that the following: In the stable oil film flow state, the oil film thickness shows a decreasing trend with increase in rotation speed and an increasing trend with increase in the lubricating oil flow. Particularly, comparison with the experimental work shows that the proposed numerical model based on theoretical study to solve unsteady oil film motion is a valuable technical means for the study of oil film movement mechanism and the design of actual bearing chamber.

For the linear modeling problem of multivariable system of aero-engine, considering the coupling between parameters, a multivariable maximum likelihood (ML) estimation method is researched. An improved expectation-maximization (EM) algorithm integrated genetic algorithm (GA) is proposed and applied to the process of ML identification of frequency domain. The amplitude, harmonic and phase vectors of odd-odd multi-sine exciting signal are designed and optimized. With the application of the proposed method, multivariable linear models of aero-engine at different operation states in flight envelope are established from nonlinear component-level model. The precision is demonstrated through simulations comparing to nonlinear model.

Active control techniques are widely researched to expand the stable operating range of axial flow compressors in aero-engines. First, an active controller using closed-coupled valve as actuator has been analyzed using numerical simulation. Analysis results showed that the stability of the controller is affected by system states under large B-parameter of compression system and need a larger control gain besides. Second, using closed-coupled valve and throttle as actuators simultaneously, a novel active control strategy has been proposed. Throttle feedback control is used to decrease the nominal B-parameter of compression system to improve control performance of closed-coupled valve controller. Lastly, numerical simulation has been carried out to evaluate the proposed control strategy. Simulation results showed that the novel controller extends the stable operation range of compression system greatly.

The efficacy of introducing mixing promoting small-scale vortices by two rectangular tabs, of aspect ratio 1.0, 1.5 and 2.0, placed at diametrically opposite locations at the exit of a Mach 1.73 convergent–divergent circular nozzle has been experimentally investigated, for NPRs from 4 to 8, covering overexpanded, correctly expanded and underexpanded states of the jet. The area blockage due to the each tab was 2.5% of the nozzle exit area. Keeping the blockage constant, the aspect ratio (defined as the ratio of length to width of the tab) was varied. A maximum core length reduction of 84.6% was caused by the tabs of aspect ratio 1.0, at underexpanded conditions corresponding to NPR (nozzle pressure ratio) 6. At this NPR, tabs of aspect ratio 1.5 and 2.0 caused core length reduction of 76.9% and 61.5%, respectively. The mixing promoting efficiency of aspect ratio 1.0 is found to be better than 1.5 and 2.0, at all NPRs of the present study, except NPR 5. The shadowgraph pictures of the uncontrolled and controlled jets clearly demonstrate the effectiveness of the tabs in weakening the waves in the jet core.

Designing inducer is one of the effective ways to improve the suction performance of high-speed centrifugal pumps. The operation condition including rotational speeds can affect the internal flow and external performance of high-speed centrifugal pumps with an inducer. In order to clarify the rotating cavitation performance of a centrifugal pump with a splitter-bladed inducer under different rotational speed, a centrifugal pump with a splitter-bladed inducer is investigated in the work. By using Rayleigh–Plesset equations and Mixture model, the cavitation flow of centrifugal pump is numerically simulated, as well as the external performance experimental test is carried out. It is found that the cavitation area increases with the rotational speeds. The location of the passage where cavitation is easy to appear is explored. Asymmetric cavitation behavior is observed. That, the trail of the inducer is easy to take cavitation when the rotational speed is increased to a degree, is also observed. The trend of NPSH r obtained by the simulation and experimental test is in general agreed. NPSH r increases with the rotational speed, which means that the anti-cavitation performance of the pump is deteriorated with the rotational speed.

Global fight against terror, and the rapidly changing geopolitical situations, raise hot debates on urgently needed new designs and operational modes of efficient, low-cost, Jet-Engine-Steered (JES) strike drones, and about the expected roles of future UCLASS (Unmanned, Carrier-Launched, Surveillance & Strike), while current UCAV (Unmanned Combat Air Vehicles) have failed to perform the needed strike missions. The role of the jet-engine community in this rapidly unfolding geopolitical situation is reviewed in the main text and in the Appendix.

Fuel cell based power systems have high energy density. However, using H 2 gas as fuel and O 2 as oxidizer in aerospace, UAV or underwater like an AIP (Air Independent Propulsion) environment has restrictions in terms of efficient storage. The direct borohydride hydrogen peroxide fuel cell (DBPFC) which uses aqueous NaBH 4 solution as fuel and H 2 O 2 solution as oxidizer has great advantages over the H 2 /O 2 fuel cell in terms of storage efficiency, energy density and power density. These excellent characteristics make the DBPFC an appropriate power source and propulsion system for AIP systems. In this study, lightweight magnesium bipolar plates for DBPFC has been fabricated and evaluated for application in unmanned underwater vehicles. Although magnesium has many favorable properties such as lightweight, high electric conductivity and machinability, low corrosion resistance restricted its use as a bipolar plate. Corrosion resistive metal, Au electroplated magnesium bipolar plates exhibited the highest power density and the promising candidate for future aerospace, UAV and underwater propulsion systems.

Conceptual design of a launch vehicle with a hybrid rocket engine (HRE) has been implemented using design informatics approach in order to investigate the feasibility of a single-stage hybrid rocket. Two test design problems were formulated by using two objective functions: maximization of downrange and minimization of initial gross weight, seven design variables which describe geometry and initial conditions, and one constraint relative to target altitude. The optimization result reveals the economical performance of hybrid rocket is limited with HRE in terms of the maximum downrange achievable. Moreover, the data-mining result indicates the mechanism of design-variable behavior.