Showing papers by "Philip Geoffrey Saffman published in 1974"
TL;DR: In this paper, a series of measurements of trailing vortices behind lifting hydrofoils is described, using a laser-Doppler velocimeter to measure two components of velocity in the vortex wake.
Abstract: A series of measurements of trailing vortices behind lifting hydrofoils is described. These measurements were made in the Caltech Free-Surface Water Tunnel, using a laser-Doppler velocimeter to measure two components of velocity in the vortex wake. Two different model planforms were tested, and measurements were made at several free-stream velocities and angles of attack for each. Velocity profiles were measured at distances downstream of the model of from five to sixty chord lengths. These measurements are the first results of a continuing experimental programme.
In § 3 of this paper, the theory of trailing vortices is discussed. The effects of ‘vortex wandering’ upon the measurements are computed, and the corrected results are seen to be in reasonable agreement with the theory.
156 citations
TL;DR: In this article, a set of equations for the calculation of turbulent shear flows is presented, which can be modified to allow for the inclusion of viscosity, compressibility and density variations.
Abstract: A set of equations for the calculation of turbulent shear flows is presented. It is shown how the equations can be modified to allow for the inclusion of viscosity, compressibility and density variations. Some results of numerical computations are given. The constant in the law of the wall is predicted to within 10% for flow over a perfectly smooth wall, and a dependence on wall roughness is obtained. The empirical law of the wall for compressible flow is also shown to be a consequence of the equations.
36 citations
TL;DR: In this paper, it was shown that the instability predicted by the cut-off approximation is spurious and cannot be used to give a complete discussion of stability in the case of a hollow vortex.
Abstract: We show by considering the special case of a hollow vortex that the cut-off approximation cannot be used to give a complete discussion of stability. In particular we show that in this case the instability predicted by the cut-off approximation is spurious.
22 citations
01 Jan 1974
TL;DR: The saturated superfluid film is capable of acting as a siphon, allowing the superfluid to drain out of any containing vessel to find the lowest available gravitational level, owing to the Bernoulli effect as discussed by the authors.
Abstract: The saturated superfluid film is capable of acting as a siphon, allowing the superfluid to drain out of any containing vessel to find the lowest available gravitational level. As in any siphon, the pressure in the film is lower when it is flowing than when it is at rest, owing to the Bernoulli effect. Since the film has a free surface which presumably cannot support a pressure discontinuity, it was expected that the flowing film would collapse on itself, like a siphon with flimsy walls. In particular, at typical film flow velocities a reduction in thickness of about one-quarter was expected.1
1 citations