Numerical aerodynamic investigations on stratospheric airships of different tail configurations
Numerical investigations on stratospheric airships of different tail configurations are conducted based on the Reynolds-averaged N-S equations and k-ω SST turbulent model in the condition of the same volume and total area of the tails. The influence of tail configurations on the force and moment characteristics as well as flow phenomena on both hull and fins are analyzed. In particular, the hull-fin mutual interference effect is discussed compared to the bare hull performance. It is found that a cross-shaped tail produces a superior lift characteristic and stability at high angle but greater drag due to horizontal fins, both in pitch and yaw channels than the inverted Y and X shaped tail. The hull-fin interference generates additional hull lift, drag and an offsetting moment and causes side edge separation on the suction side of horizontal (side) fins in the cross (inverted Y and X shaped) tail configuration. The inverted Y-shaped tail provides the greatest interference drag. These investigations serve to provide references for airship configuration design.
A METHODOLOGY FOR DETERMINATION OF BASELINE SPECIFICATIONS OF A NON -RIGID AIRSHIP
This paper presents a methodology for arriving at the baseline specifications of a non -rigid airship of conventional configuration, given the performance and operational requirements. Specifi cally, the methodology calcula tes the envelope volume required to carry a use r- specified payload, and also arri ves at the mass breakdown, a nd per forman ce estimates . Alternatively, the payload that can be carried by an airship of specified envelope volume can also be estimated. Sensitivity of parameters such as pressure altitude, ambient temperature, cruising speed, Helium purity level, engine power, env elope length to diameter ratio etc. on the payload available or envelope volume requi red can also be determined . T he baseline specifications of two airships for transportation of goods and passengers under hot and hi gh conditions obtained using this method ology are presented . Results of sensitivity analysis for one airship are also discussed. 1 NOMENCLATURE
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.