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-   -   Relaltionship between pressure drop and drag force (http://www.cfd-online.com/Forums/main/8987-relaltionship-between-pressure-drop-drag-force.html)

 Li April 7, 2005 22:14

Relaltionship between pressure drop and drag force

Hi,

I am simulation flow across a tube bank. Based on force balance in a closed system, the pressure drop per row of tubes and the total drag force (sum of friction and form drag) per ros should have the relationship of:

DeltaP*A_T=Drag force Where A_T is the minimum transverse flow area between tubes.

Am I right? I found my simulation results do not agree with this. Can anyone help me? Thank you very much.

Li

 Alexander Starostin April 12, 2005 09:57

Re: Relaltionship between pressure drop and drag f

dP*S=drag force*L

 Li April 12, 2005 20:27

Re: Relaltionship between pressure drop and drag f

Alex, Can you explain the S and L in your equation? It seems that the left hand side is a force (if s is a distance) and the right hand side is energy. What is the equation based on? Thank you for your help. Zhihua

 Rami April 13, 2005 03:12

Re: Relaltionship between pressure drop and drag f

Li,

We are also doing simulations based on tube banks resistance (using correlations by Zukauskas), so I would like to help, but am not clear about your tratment. Are you simulating the detailed flow, i.e., resolving each tube neighborhood by many cells or using a porous medium approach (the latter is our approach)? In the first approach the drag force arises naturally as the net normal-to-the-tubes force. In the latter, you usually model the pressure gradient, and from that - calculate the drag force per REV (Representative Elementary Volume). This volume is usually given by Sx*Sy*L, where Sx and Sy are the pitches of the tube array in both directions and L is the tube length.

If you wish, I would send you an extract of a detailed description of the model we use.

I hope this helps.

 Li April 13, 2005 11:01

Re: Relaltionship between pressure drop and drag f

Hi Rami,

I am using a periodic boundary condition to simulate the flow field at the inner rows of a tube bank, i.e., the fully developed region. The pressure drop per row of tubes is equal to the linear pressure gradient times the longitudinal distance. The drag force can be calculated based on the integration of pressur force/wall shear stress around a tube. My calculated Eu based on the pressure drop per row fits Zukauskas correlation very well (10% difference). Because the pressure drop is caused by drag, I tried to relate my pressure drop with the drag force. My questions is: What is the relationship?

Thank you very much!

Zhihua

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