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.
Taylor vortices between eccentric cylinders
The critical Taylor number and the critical wavelength of Taylor vortices has been measured as a function of the eccentricity. It has been found that in this apparatus the critical Taylor number increases steadily as a function of eccentricity. The critical wavelength was found to remain nearly constant for small e and to decrease with larger e. Separated flow, as observed from above, was found to be in qualitative agreement with the prediction of Kamal.
UV-B radiometry and dosimetry for solar measurements.
Biologically effective irradiance or dose of solar UV radiation was determined using a spectroradiometer, two broadband radiometers and two types of passive UV-dosimeters. The absolute erythema irradiance and the actinic irradiance were calculated from the solar spectrum measured with the spectroradiometer. It was demonstrated that the erythema irradiance is proportional to the actinic irradiance of solar radiation. The erythema irradiance was also determined using the two broadband radiometers which utilize a filter transmitting erythema spectra. Personal UV-dosimeters such as polysulphone and CR-39 were used to determine the erythema dose for a selected period of time. These results were used to estimate the accuracy of the broadband radiometers and UV-dosimeters. It was found that the results obtained from the broadband radiometers deviate from the absolute erythema irradiance by less than 20% during clear days between the hours of 11:00 and 13:00 Eastern Standard Time (EST) in Australia. The assessment of the erythema dose using passive dosimeters such as polysulphone and CR-39 could introduce an error as high as 40% if the calibration was not performed before undertaking experimental measurements.