Plaque à Trous

The principle of worst action applied to a perforated plate.

The principle of operation is the following: the fluid put in speed in the section restriction that is imposed to it, degrades its kinetic energy downstream by the sudden enlargement effect.
This energy degradation is often accompanied by chaotic areas and instabilities, as it can be seen on the video below.

 

Description of a vistemboir adapted to perforated plates.

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Significant speed differences are created in the cavity, between supersonic central flow and peripheral subsonic flows. This speed difference is greater that the average speed of molecules. These molecular movements should be deeply affected.
Flows are blocked by sonic throats, so they are independent. A brutal mixture with very intense momentum exchanges is imposed. This flow is stable and the degradation of the kinetic energy is fast and more important than in a single sudden enlargement.
Fluid mechanics specialist will recognize that the performance of such a device is appalling. It’s a very bad fluid mechanics; however it will prove to be very useful.

About the Author Michel Pluviose

Michel Pluviose is Honorary Professor of Le Conservatoire National des Arts et Métiers (CNAM), and formerly Chair of Turbomachines who received his Doctor of Sciences from Université Pierre et Marie Curie - Paris VI. A hands-on engineer, Michel has worked with leading institutions, including as an engineer at Hispano-Suiza, SNECMA, Head of the laboratory at ATTAG (Association technique pour les turbomachines et turbines à gaz), Manager for compressible fluid activities at CETIM (Centre technique des industries mécaniques), and manager of the treaty « Machines hydrauliques et thermiques » at the « Techniques de l’Ingénieur » publications.

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