Diameter number

Physical key figure
Surname	Diameter number
Formula symbol	${\displaystyle {\mathit {\delta }}}$
dimension	dimensionless
definition	${\displaystyle \delta ={\frac {D}{\sqrt {\frac {\textstyle {4\cdot {\dot {V}}}}{\textstyle {\pi {\sqrt {2\cdot Y}}}}}}}}$
${\displaystyle D}$ Impeller outer diameter ${\displaystyle {\dot {V}}}$ Volume flow ${\displaystyle Y}$ specific nozzle work
scope of application	Turbo machines

The number of diameters ("delta") is a dimensionless number for characterizing turbomachines . ${\displaystyle \delta }$

It relates the outside diameter of the machine's impeller to the calculated diameter of an equivalent nozzle . With an equivalent nozzle , the volume flow exiting the impeller would cause a pressure difference to occur which corresponds to the specific nozzle work of the turbomachine : ${\displaystyle D}$ ${\displaystyle {\dot {V}}}$ ${\displaystyle Y}$

${\displaystyle \delta ={\frac {D}{\sqrt {\frac {\textstyle {4\cdot {\dot {V}}}}{\textstyle {\pi {\sqrt {2\cdot Y}}}}}}}}$

Using the flow machine parameters, flow rate and pressure , one can also write: ${\displaystyle \varphi }$ ${\displaystyle \psi }$

${\displaystyle \Leftrightarrow \delta ={\sqrt {\frac {\sqrt {\psi }}{\varphi }}}}$

The number of diameters is important for the Cordier diagram , in which the running number is plotted against the number of diameters and provides information on the types of fluid-flow machines with which the best efficiencies can be achieved for given requirements .

literature

• Willi Bohl: Turbo machines 1, structure and mode of operation . Vogel, Würzburg 1998, ISBN 3802317378 .
• Herbert Sigloch: Fluid flow machines , basics and applications . Hanser, Munich 2009, ISBN 9783446418769 .

Individual evidence

1. ^ Herbert Sigloch: Fluid flow machines , fundamentals and applications . Hanser, Munich 2009, p. 111.