Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1997-03-04
1998-11-17
Dougherty, Thomas M.
Electrical generator or motor structure
Dynamoelectric
Rotary
277 1, 277 53, 277 55, 251127, 251298, 122 32, 122235F, F22B 116, F16K 4702
Patent
active
058380833
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device for breaking eddies at a surface submerged by a turbulent flow.
At surfaces bathed or submerged by gas or liquid, above certain flow velocities, turbulence occurs that is characterized by increasing eddy size as the flow velocity rises. In unfavorable cases, the forces involved in the eddy development can cause the submerged surfaces to flutter. Particularly in machines that rotate at high speed, such forces can cause undesired interference, especially natural precession, nutation and bending frequencies of the system.
Such interference makes itself especially seriously felt in centrifuges, if they are equipped with touchless magnetic bearings in order to attain high long-term speeds. It is then necessary to compensate for the incident interfering forces by means of electronically stabilizing the magnet bearing, which produces energy losses.
It is the object of the invention to disclose a device with whose aid the forces resulting from turbulence eddies on a submerged surface can be rendered inoperative within the natural frequency range of the submerged surface or its suspension, without having to accept increased energy losses. In particular, radial forces resulting from turbulence eddies in a magnetically supported cylindrical rotor that are in the range of the natural bearing frequency of the magnet bearing system should be intercepted.
The concept of the invention is based on the thought that turbulence eddies have a disruptive effect on the stable position of a submerged surface if the frequency spectrum of the turbulence eddies, or the spectrum of the forces involved in the eddies and acting on the submerged surface, and in particular the frequency spectrum of the radial forces engaging a magnetically supported rotor and the natural frequency spectrum of the surface of magnet bearing system mutually overlap. The idea of the invention is that by breaking the eddies or in other words making them smaller, their frequency spectrum can be shifted into a range that is sufficiently far above the critical natural frequencies of the system. At a slight distance from the submerged surface, a periodically structured wall is used; as a structure, periodically distributed bumps or lands on the wall and/or openings in the wall can be considered in particular; the dimensions and mutual spacings of the structural elements and the distance of the wall from the submerged surface are essentially equal. The distance of the wall from the submerged surface determines the maximum eddy size that still occurs or is still allowable for the intended application.
The mounting of a perforated, sievelike or gridlike structured wall, in the vicinity of the submerged surface, especially a surface rotating at high speed, considerably impedes the development of relatively long and correspondingly low-frequency eddies in the critical natural frequency range and leads to calming of the dynamic system performance, especially under the conditions of magnetic bearing.
The advantages of the device of the invention can be applied successfully to a turbulent flow through tubes as well, and to airborne or floating bodies.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in further detail below in terms of exemplary embodiments that are schematically shown in the drawing. In detail, the drawing shows the following:
FIG. 1, a perforated wall in front of a surface submerged by a tangential flow;
FIG. 2, a rotating, magnetically supported cylinder with a perforated wall;
FIG. 3, a flow tube with a perforated wall on the inside;
FIG. 4, the submerged surface of an airborne or floating body with a perforated wall disposed in the flow space.
BRIEF DESCRIPTION OF THE INVENTION
FIG. 1 shows a wall 1, structured in the form of a perforated metal sheet, which is disposed at a distance 2 from a submerged surface 3. The flow direction of the flowing medium between the surface and the wall is marked with arrows 4. The distance 2 between the wall 1 and surface 3 determine
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Fremerey Johan K.
Polachowski Stephan
Reiff Heinrich
Dougherty Thomas M.
Forschungszentrum Julich GmbH
Nguyen Tran N.
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