1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Nondimensionlization of Pressure

  1. Aug 21, 2007 #1
    Hi all.
    When I read through text in fluid mechanics, I see various ways of non-dimensionlising the pressure. (Please see the figure)

    To me, non-dimensionlize a quantity is to make it of order unity to facilitate the mathematical processes needed afterwards.
    So, I can understand why density*gravity*H is used as a characteristic scale to non-dimensionlize the pressure since it is the maximum hydrostatic pressure.

    But I don't understand why density*U^2 is used to non-dimensionalize the pressure as well? In what situation is this nondimensionlization valid?

    What about the P(infinity), what is it?

    Attached Files:

  2. jcsd
  3. Aug 21, 2007 #2


    User Avatar
    Science Advisor

    The second two numbers are actually referred to as the Euler number (ref http://en.wikipedia.org/wiki/Euler_number_(physics)). It is another dimensionless number. I don't really use it myself (I don't need to stray too much from the Reynolds number), but my handy, dandy fluids reference lists it as a useful number when dealing with pressure differences, such as in cavitation analyses. Actually, the third version you show is what is listed for a cavitation analysis (without a .5 factor) where the P is actually a reference pressure and the [tex]P_{\infinity}[/tex] is the vapor pressure of the working fluid.

    Omega Engineering has a neat poster you can request that has a ton of dimensionless numbers and their uses. You can also look at a lot of them here on Wiki: http://en.wikipedia.org/wiki/Category:Dimensionless_numbers
  4. Aug 21, 2007 #3
    Thanks. But why density * U^2 is used to non-dimensionlize the pressure? I don't understand the rationale behind...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Nondimensionlization of Pressure
  1. Pressure Drop (Replies: 7)

  2. Static Pressure (Replies: 31)

  3. Stagnation pressure (Replies: 9)