Studies of Aerodynamic Drag.
Final rept. 1 Apr 79-30 Sep 82,
CAMBRIDGE UNIV (ENGLAND) CAVENDISH LAB
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Earlier workers reported that the viscosity of gases can be changed appreciably by radioactive irradiation, offering a possible means of achieving drag reduction in flight. A precision skin friction drag balance and torsion disc viscometer were developed to investigate this effect. It is shown that, with practical radiation levels, irradiation has a negligibly small effect on viscosity and skin friction drag both laminar and turbulent. This agrees with theoretical estimates of the change in viscosity due to ionisation. It has also been reported that turbulent gas flows align polar or polarisable molecules whose motion then gives rise to detectable electromagnetic radiation. A study was made of this phenomenon with a view to applications in monitoring the structure of turbulent gas glows during drag reduction experiments. It is concluded that the previous interpretation was erroneous and that the probes used were responding to vibration rather than to electromagnetic radiation. Calculations suggests that any electromagnetic signal will be at least 120 dB below the background noise level. The equipment and electronics developed in the course of the research can be used for accurate, relative measurements of skin friction drag and viscosity. The operation of the viscometer is particularly simple, with the logarithmic decrement being determined automatically. The relative viscosity is calculated using a simple formula, derived from earlier theoretical work.
- Test Facilities, Equipment and Methods
- Fluid Mechanics