Comparing pressure loss to Blasius

In summary, the speaker has conducted a CFD simulation in Fluent for turbulent pipe flow and plotted static pressure against distance. They were advised to compare the pressure loss to Blasius and Darcy equations, but the speaker is unsure how to do so. They mention using the Blasius friction factor and calculating it from the pressure drop, but someone corrects them and suggests using the Darcy-Weisbach equation instead. The speaker is still confused and asks for further clarification on how to compare their results to the theoretical pressure loss using these equations.
  • #1
Isabella F
3
0
Hi everyone. i have done a CFD smulation in fluent for a turbulent pipe flow and have plotted static pressure against distance x. from the graph i get a straight negtive gradient. i have been told that you should compare the pressure loss to Blasius equation and Darcy equation. How do i compare the pressure loss to this. thank you. the fluid is water, diameter is 50mm, inlet velocity is 1m/s and reynolds number 49760.
heres is the xy plot i get.

s63xox.jpg
 
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  • #2
Well that seems awfully silly to compare to Blasius because (A) it is pipe flow, so Blasius is not representative, and (B) it is turbulent, so Blasius doesn't apply.

Comparing to Darcy-Weisbach should be straightforward though.
 
  • #3
The Blasius friction factor f=0.079/(Re^0.25).
Is there a way to calculate friction factor from the presure drop? that is what i think i need to do and then compare to blasius friction.
 
  • #4
Ah, I thought you were referring to the Blasius boundary layer. My mistake.
 
  • #5
How do i do this then. I am a bit confused.
 
  • #6
Just look up the Darcy-Weisbach equation. It is very straightforward. Use it and the Blasius correlations to approximate the theoretical pressure loss (head loss) and compare to your results.
 

1. How is pressure loss calculated in the Blasius equation?

The Blasius equation is a widely used empirical formula that relates pressure loss to the Reynolds number and the geometry of the flow. It is calculated by taking into account the friction factor, fluid density, flow velocity, and pipe diameter.

2. What is the significance of comparing pressure loss to Blasius?

Comparing pressure loss to Blasius allows for a quick estimation of the expected pressure drop in a fluid flow based on known parameters such as the fluid and pipe properties. This can be useful in designing efficient and cost-effective piping systems.

3. How accurate is the Blasius equation in predicting pressure loss?

The accuracy of the Blasius equation depends on the specific flow conditions and the assumptions made in its derivation. In general, it is most accurate for laminar flow and becomes less accurate as the flow transitions to turbulent.

4. Are there any limitations to using the Blasius equation?

Yes, the Blasius equation is limited to fluid flows that are fully developed, steady, and incompressible. It also assumes a smooth pipe surface and does not take into account any external factors that may affect pressure loss, such as fittings or changes in pipe diameter.

5. How does the Blasius equation compare to other pressure loss equations?

The Blasius equation is one of the most widely used pressure loss equations due to its simplicity and accuracy for laminar flows. However, for turbulent flows, other equations, such as the Colebrook-White equation, may be more accurate. It is always important to carefully consider the flow conditions and choose the most appropriate equation for accurate results.

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