In fluent there are several options for pressure, static dynamic, total. May any one suggest which one to consider if I am looking for pressure drop for flow in a pipe.
I initially went with static pressure at inlet-static pressure at outlet. (assuming the the dynamic pressure will almost be same as my flow is through constant cross section pipe)
However I found there is difference in values of dynamic pressure at inlet and exit (though minor). SO which pressure should I consider for appropriate pressure drop.
You should be considering total pressure. And dynamic pressure will not remain constant as the flow will move through the pipe. The velocity profile is changing the dynamic pressure will change. At outlet we specify static pressure.
You should be considering total pressure. And dynamic pressure will not remain constant as the flow will move through the pipe. The velocity profile is changing the dynamic pressure will change. At outlet we specify static pressure.
Hi,
I agree the velocity profile is changing , but then isn't the average velocity always same at every cross section. Just considering the Bernoulli s equations, for a case in which pipe the horizontal and uniform cross section. Then in that case we will have vin =v out so which means that dynamic pressure shouldn't be same???
You can use anyone you like and you will find same results.Your small change is due to numerical errors that always exist and will diminish as you refine the grid.
Please note for pipe flow you DO NOT need outlet BC because problem is Parabolic and the process of solving is marching forward.
You consider total pressure plot first as well as u can plot static pressure and merge both data through tech plot or in fluent too then u easily figure out the difference and in this way you also analyze how the dynamic pressure changes across the flow.
Pressure drop for the horizontal pipe is equal to the pressure loss due to the viscous effects, and it is given (see any Fluid Mechanics textbook),
Dp=f(L/D) rho Va^2/2
Where rho Va^2/2 is the dynamic pressure, and Va is the average velocity of fluid equal to half of the maximum velocity profile, r=0, for laminar flow and horizontal pipe. L is the length of pipe and D diameter, f is the friction factor, and rho the fluid density.
if your pipe is vertical, you have some hydrostatic pressure to consider, however you can use to your BC the velocity inlet and poressure outlet , it gives good results
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