Abstract: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.

The small amplitude rheological properties of doughs of different compositions were measured using a dynamic rheometer. In the first study, the effect of water, flour, and added gluten on the dynamic properties was investigated. Frequency sweep was carried out in the range of 0. 1 to 100 s−1 at an applied strain of 0. 1%. Storage (G') and loss (G”) moduli for each composition were recorded. The storage modulus versus frequency plots were a series of parallel curves indicating that the moisture‐to‐flour ratio was the most important parameter. The loss modulus versus frequency plot showed a falling‐off after a frequency of 40 s−1. A plot of tan δ versus frequency indicated a more elastic dough at shorter time

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A video camera tracer technique (T. A. Huangand G. A. Campbell, paper Although literature results on film blowing deformation are available, '-I6 most of the work was conducted on a small line where throughput and cooling rates are limited. Recently, we initiated a research program aimed toward a fundamental understanding of the process. The effect of extrusion variables upon stretching and cooling histories for LDPE and LLDPE is discussed elsewhere. *' DEFORMATIONAL, HISTORY OF LLDPEILDPE BLENDSFor LLDPE/LDPE blends, data of deformational history on the blown film equipment are not available in the literature. Recently, it became a plastics industry practice to add small amounts of LDPE into LLDPE for stabilization of the bubble and for improvement of LLDPE film opticals. Also, the addition of small amounts of LLDPE into LDPE reduces bubble breaks and improves drawdown characteristics. The purpose of this work is to quantify the changes in strain and strain rate histories caused by these additions of resin types. INTRODUCTIONMATERIAL DATA Blown film technology has been practiced in industry for many years. It is generally recognized that stretching and cooling histories experienced by the fluid element between die and frost line have an important effect on determining final film properties.

We present an experimental visualization study of centrifugal spinning, which is a novel method of producing nanofibers. The investigation was conducted using Newtonian and viscoelastic fluids to study the effect of viscoelasticity, driving force, and the flow rate on the initial thinning behavior, jet contour shapes, and radii. Boger fluids based on Newtonian polybutene and viscoelastic polyisobutylene were utilized as test fluids in the current study. Our results reveal that increasing the viscoelasticity leads to a faster initial thinning of the polymer jet. However, the effect is strongly coupled with the rotation speed, and due to a faster increase in extensional viscosity for highly viscoelastic fluids, the thinning slows down with the increase in the angular velocity. Initial thinning is shown to be faster for the lower flow rates. Viscoelasticity and centrifugal force have a significant influence on the jet contour radii. The maximum radius will decrease for more viscoelastic fluids, and with the increase in angular velocity due to the development of the elastic hoop stress. The comparison of experiments with the discretized element modeling with the FENE-P model confirms the model predictive potential for the thinning behavior. Finally, the centrifugal spinning experiments are compared to electrospinning in order to observe a qualitative similarity.