Stability of fluid flow in a cylindrical annulus

Helical flow in an annulus between two coaxial cylinders is investigated with regard to its stability against the formation of helical vortices of the type known as Taylor's annular vortices. Assuming the annulus to be small and the velocities to vary linearly with radius, it is shown that the problem can be reduced to the classical case of flow between two rotating cylinders. An appropriate stability criterion for helical flows is derived from Rayleigh's stability criterion applicable to such flows

An explanation of the instability of the free vortex cores occurring over delta winds with raised edges

By rolling up the surfaces of discontinuity originating from the leading edge of delta wings, free vortex cores are formed above the wing. In case of greater angles of incidence, the flow in these vortex cores shows an instability which abruptly produces strong turbulence. In the present paper an explanation is given of this instability being a "frictionless instability" of the vortex core flow by increasing helical interference vortices. The occurring vortex core flows are calculated and investigated for stability by means of a stability criterion concerning flows with helical streamlines given by H. Ludwieg

Instrument for measuring the wall shearing stress of turbulent boundary layers

It is shown that at a smooth wall in a turbulent boundary layer the velocity profile next to the wall is dependent, aside from the material constants of the flowing medium, only on the shearing stress transmitted to the wall, even with pressure rise or with pressure drop. Consequently, the heat transfer of a small element that is built into the wall and has a higher temperature than that of the flowing medium is a measure of the wall shearing stress. Theoretical considerations indicate that the wall shearing stress of the boundary layer can be defined by means of a heat-transfer measurement with an instrument mounted in the wall. Such an instrument is described. The calibration curve and its directional sensitivity curve are indicated. It permits the determination of the wall shearing stress in magnitude and direction

Ein Gerät zur Messung der Wandschubspannung

"It is shown that at a smooth wall in a turbulent boundary layer the velocity profile next to the wall is dependent, aside from the material constants of the flowing medium, only on the shearing stress transmitted to the wall, even with pressure rise or with pressure drop. Consequently, the heat transfer of a small element that is built into the wall and has a higher temperature than that of the flowing medium is a measure of the wall shearing stress. Theoretical considerations indicate that the wall shearing stress of the boundary layer can be defined by means of a heat-transfer measurement with an instrument mounted in the wall" (p. 1)

NACA Technical Memorandums

In the vicinity of a body in a wind tunnel the displacement effect of the wake, due to the finite dimensions of the stream, produces a pressure gradient which evokes a change of drag. In incompressible flow this change of drag is so small, in general, that one does not have to take it into account in wind-tunnel measurements; however, in compressible flow it beoomes considerably larger, so that a correction factor is necessary for measured values. Correction factors for a closed tunnel and an open jet with circular cross sections are calculated and compared with the drag - corrections already bown for high-speed tunnnels