The present study aimed at assessing a novel annular-ducted fan lift system for VTOL aircraft through computational fluid dynamics (CFD) simulations. The power and lift efficiency of the lift fan system in hover mode, the lift and drag in transition mode, the drag and flight speed of the aircraft in cruise mode and the pneumatic coupling of the tip turbine and jet exhaust were studied. The results show that the annular-ducted fan lift system can have higher lift efficiency compared to the rotor of the Apache helicopter; the smooth transition from vertical takeoff to cruise flight needs some extra forward thrust to overcome a low peak of drag; the aircraft with the lift fan system enclosed during cruise flight theoretically may fly faster than helicopters and tiltrotors based on aerodynamic drag prediction, due to the elimination of rotor drag and compressibility effects on the rotor blade tips; and pneumatic coupling of the tip turbine and jet exhaust of a 300 m/s velocity can provide enough moment to spin the lift fan. The CFD results provide insight for future experimental study of the annular-ducted lift fan VTOL aircraft.

Numerous materials have been proposed for thermoluminescence dosemeter, and the example of highest sensitivity is cited as magnesium orthosilicate doped with terbium (Mg₂SiO₄:Tb). Nevertheless, the material is currently not commercially attractive because the sensitivity varies greatly with synthesis techniques. This is a multi-parameter problem, and the current work explores some of the conditions required to consistently enhance the response. These new results show that to get a high TL response, Mg₂SiO₄:Tb should be prepared at a high temperature of at least 1500°C, for sintering times of several hours. In the current example, the optimum time was 6 h. Signals also vary with the terbium activator concentration, and good responses were achieved with a concentration of Tb at 5 wt %. Overall, this suggests that with careful preparation, the potentially high dosimetry performance might be exploited. The inherent problem of concentration quenching is considered, and the potential benefits of processing the powder with pulse laser annealing are reviewed in the light of successful luminescence and laser studies for rare-earth-doped laser materials.

The effects of various parameters on the hovering performance of an annular lift fan aircraft are investigated by using numerical scheme. The pitch angle, thickness, aspect ratio (chord length), number of blades, and radius of duct inlet lip are explored to optimize the figure of merit. The annular lift fan is also compared with a conventional circular lift fan of the same features with the same disc loading and similar geometry. The simulation results show that the pitch angle of 27°, the thickness of 4% chord length, the aspect ratio of 3.5~4.0, 32 blades, and the radius of inlet lip of 4.7% generate the maximum figure of merit of 0.733. The optimized configuration can be used for further studies of the annular lift fan aircraft.

A new annular lift fan configuration that has very high lift efficiency is explored by using a numerical scheme. The inlet lip radius and diffuser angle are maximized by semicircle duct walls and the location of the lift fan is moved from the throat to the diffuser area to maximize the diffusion effect of the ducted fan. The improved lift fan achieves the figure of merit of 0.772 and the power loading of 9.03 lbs/hp without ground effect, very close to the theoretical limit. Under the ground effect, the figure of merit reaches 0.822 with the power loading of 9.62 lbs/hp. The improved lift efficiency deteriorates the transition characteristics with higher momentum drag and pitching moment. However, with the aid of jet thrusts directly providing part of the lift during transition, the peak of momentum drag and pitching moment can be lowered. A total thrust to weight ratio of 0.7 is enough for all of the requirements in transition and in hover and for the maximum speed of 0.75 Mach in cruise flight.

The present study aimed at studying the transition of annular lift fan aircraft through computational fluid dynamics (CFD) simulations. The oscillations of lift and drag, the optimization for the figure of merit, and the characteristics of drag, yawing, rolling and pitching moments in transition are studied. The results show that a two-stage upper and lower fan lift system can generate oscillations of lift and drag in transition, while a single-stage inner and outer fan lift system can eliminate the oscillations. The characteristics of momentum drag of the single-stage fans in transition are similar to that of the two-stage fans, but with the peak of drag lowered from 0.63 to 0.4 of the aircraft weight. The strategy to start transition from a negative angle of attack −21° further reduces the peak of drag to 0.29 of the weight. The strategy also reduces the peak of pitching torque, which needs upward extra thrusts of 0.39 of the weight to eliminate. The peak of rolling moment in transition needs differential upward thrusts of 0.04 of the weight to eliminate. The requirements for extra thrusts in transition lead to a total thrust–weight ratio of 0.7, which makes the aircraft more efficient for high speed cruise flight (higher than 0.7 Ma).

The annular lift fan aircraft is a new conceptual vertical takeoff and landing (VTOL) vehicle for which the tremendous momentum drag and pitching moment in transition is a big problem to overcome. In this study, different strut configurations and transitional strategies for the annular lift fan aircraft are numerically investigated using computational fluid dynamics (CFD) software. The results show that the longitudinal struts can significantly reduce the oscillations of lift and drag caused by the interactions between the radial struts and the incoming flow and that the gliding transition strategy reduces the total required thrust by 47% without the need for a skirt. This gliding transition is also faster, taking only about 20 seconds to complete because part of the thrust can be used for the forward acceleration.