Moody chart

The Moody diagram is an important diagram for fluid mechanics applications, which was empirically created in 1944 by the American engineer Lewis F. Moody . It enables the calculation of the pressure loss in a straight pipeline with fully developed laminar or turbulent flow .

On a logarithmic scale, it shows the relationship between the unitless quantities

Coefficient of friction (vertical axis)

{\ displaystyle \ lambda}

Reynolds number (horizontal axis) and

Reciprocal value or, in the figure, the relative roughness (parameters of the resulting family of curves ; with the diameter of the pipe and the mean roughness depth or ). ${\ displaystyle {\ frac {d} {R_ {z}}}}$ ${\ displaystyle {\ frac {d} {k}}}$ ${\ displaystyle d}$ ${\ displaystyle R_ {z}}$ ${\ displaystyle k}$

Limits for constancy and for hydraulically smooth behavior

The Moody diagram shows a clear difference between the flow behavior of laminar and turbulent flow.

For turbulent flow, a constant limit can be seen ("limit curve" in the figure), from which the coefficient of friction for a fixed relative roughness remains constant with increasing Reynolds number (the coefficient of friction is independent of speed and viscosity for the corresponding range of Reynolds number ).

A limit for hydraulically smooth behavior is also recognizable: the coefficient of friction here has a minimum value for a certain Reynolds number, which is not fallen below even for a very small mean roughness depth . In this area , i. H. the grooves in the pipe wall remain entirely within the thick, tough sub- layer with high friction . ${\ displaystyle R_ {z, max} \ leq \ delta}$ ${\ displaystyle \ delta}$

literature

Lewis F. Moody: Friction Factors for Pipe Flow . In: Transactions of the ASME November 1944, pp. 671–684 (English, digitized version in the web archive 2012-01-06 ( memento from January 6, 2012 in the Internet archive ) [PDF; 1.8 MB ]).

Siekmann, Thamsen: Fluid Mechanics: Basics . 2nd Edition. Springer, Berlin 2000, ISBN 978-3-540-66851-0 .