Viscous Action Research Articles

Aerodynamic of Nonuniform Flows as Related to an Airfoil Extending Through a Circular Jet

A method has been derived for the determination of the downwash in the field of an airfoil extending through a circular jet. This solution for values of downwash was then employed in lifting surface theory to determine the lift distribution on a wing extending through a circular jet. The basic approach for the downwash solution was to consider the flow resulting from the viscous action of the vortex sheet constituting the jet boundary. The method of solution is essentially based on a division of the flow thus induced by this jet boundary into parts which are even and odd with respect to the direction of flow. The analysis due to the even part alone is similar to previous theories, which in effect disregarded the odd part. Such previous results for the lift distribution based on the even part alone differ considerably from the experimental values. The results based on the total of the even and odd parts show good agreement with the experiments, illustrating the necessity of including the odd part of the flow when the segment of the wing immersed in the jet is of low aspect ratio. The problem has been solved in parametric form, so that the results may be employed to determine the characteristics of any geometry wing-jet combination at any jet velocity ratio.

Flow of a Compressible Fluid in a Thin Passage

Abstract Pressure distribution and weight-flow rate can be predicted for laminar compressible-fluid flow in a thin passage by use of the methods presented in this paper. A simplified method can be used readily when the fluid forces due to viscous action predominate over those due to acceleration of the fluid. A more complicated trial-and-error method seems to be required for larger passages where, though the flow may be laminar, the momentum effects due to acceleration of the compressible fluid are appreciable. An experimental apparatus was used to examine the validity of the analytical work. Experimental pressure distributions agree within a maximum deviation of 10 per cent with the theoretical distributions predicted by both the comprehensive and simplified theories. Experimental weight-flow rates agree within a maximum deviation of 50 per cent with predictions of the simplified theory. Dimensionless plots of pressure distribution are presented with experimental curves of flow rate versus pressure ratio for various ratios of passage length L to passage height h. These plots, together with simple equations, have been prepared for direct use by the designer.

IONOSPHERIC WIND SYSTEMS AND ELECTRON CONCENTRATIONS OF THE F LAYER

Abstract In a study of wind systems in the ionosphere, viscous stresses achieve considerable importance. A study of layer thicknesses, resulting from a specified ratio of densities at the top and bottom of the layer, indicates that the mean free path is as large as the layer thickness at 400 km. This suggests that viscous stresses reach a maximum at a lower level. Consideration of the effective portion of a layer of gas suggests a maximum of viscous action at 200 km. On the basis of observed temperature lapse rates and the proposed vertical distribution of viscous action, a simple meridional circulation is developed for ionospheric regions. This circulation is used to explain longitudinal differences observed in electron concentrations for the F2 layer. The association between the ionospheric data and the proposed circulation is considered sufficiently close to merit additional study and investigation.

Absorbing Media for Underwater Sound Measuring Tanks and Baffles

By using absorbing walls surrounding a small body of water, measuring tanks have been produced which will determine the directional properties of underwater sound instruments down to a level of 25 db below the direct beam. These absorbing media are constructed by inserting fine mesh screen or packed copper wadding in a viscous liquid such as castor oil. These obstructions result in an enhanced viscous action which is nearly independent of the frequency above 10 kilocycles. A six-inch wall can reduce the reflections by 20 db. Tanks using such absorbing media were used for testing transducers at the manufacturing plant and were used for determining the approximate characteristics of small sized instruments. Absorbing media were also used in the sound transparent dome housing the transducer and in the back of the QJB transducers.

Sir William Thomson on Molecular Dynamics 1

II. IN the present article Sir William Thomson's spring and shell molecule will be described and its theory sketched, in so far as this has been investigated with the view of getting over some of the difficulties which surround the wave theory of light. In Helmholtz's memoir on anomalous dispersion, a sketch of such a theory was published. But this new molecule differs from that of Helmholtz in several points, chiefly in the fact that absorption is not accounted for by any viscous action in the molecule dissipating the energy of vibration into low grade heat. Most readers who have ever visited the natural philosophy lecture-room in Glasgow University will recognise a very old friend in this new molecule, where they have seen it vibrating, I suppose, any time since the University occupied its present site. In appearance the molecule has been changed, but its theory as taught to the students there is identical. For a description of this molecule let us refer to page 10 of the lectures:—