It’s not all about turbulence

“Our baby is no fluid motion” said the women sitting on my sofa and watching Wallander. She was right, but I realised it quite late. I thought about why a baby turns around about its vertical axis during its delivery. Well, its simple I thought. In order to decrease the “wall friction” at the pipe close to the “nozzle exit” a turbulent flow can be imparted with a tangential motion. This will lead to a decreased pressure drop (less energy is needed to come out), a reduced friction along the pipe (less pain I suppose), and the head might deform towards an egg shape (the exit is reached earlier). Shortly after this thought experiment I realised how stupid I was. Who said that the Reynolds number is high enough to have a turbulent pipe flow? OK, I can live with idealised conditions, but how dare I to assume a high Reynolds number condition? It is more likely that the motion might be considered by means of creeping flow equations, because the baby comes out with such a slow axial velocity component, that the non-linear terms, which are one cause for turbulence, are much smaller than the viscous terms. Additionally the tangential component is comparable with the axial component, does that mean that babies experience vortex breakdown? Mmh, I was thinking quite a while, until my Wife asked me how I would dare to speak about our prospective child in terms of a highly deformable fluid. She was right, not only did I assume way too much (pipe flow, circular nozzle, turbulent flow) I also forgot that not everything around us is fluid motion. Sometimes one gets really attached to things one reads or deals with and forgets what live is all about. I hope I will at least manage to be more careful with my assumptions when solving idealised problems and don’t get lost again in thoughts towards nowhere.

PS: I just remembered that babies come out with a white substance, which also can reduce friction and damp the disturbances in the flow if the baby could be considered as a turbulent flow. It’s really hard to concentrate at parents courses if I always drift off with my thoughts.

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4 Responses to “It’s not all about turbulence”


  1. 1 Florian January 29, 2007 at 5:46 pm

    Hi,
    I found your blog via google by accident and have to admit that youve a really interesting blog 🙂
    Just saved your feed in my reader, have a nice day 🙂


  1. 1 Fontanelles and reflexion « wAnNaBe NeRd Trackback on March 26, 2007 at 9:00 pm
  2. 2 Between tears and laughs « wAnNaBe NeRd Trackback on April 3, 2007 at 5:56 am
  3. 3 We are different after all « wAnNaBe NeRd Trackback on October 31, 2007 at 8:16 pm

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