Bernoulli equation - how to get static pressure???
Ondrej
does anybody cognizant of fluid mechanics know, how to compute STATIC
pressure in a tube? (I am making venturi tube java applet). From
bernoulli is: 1/2*v^2*Rho + P(static) = const.(for horizontal location)
I know velocity v, flow space, density of fluid. First I thought, that
the static pressure could be optional, but after visiting
http://www.ce.utexas.edu/prof/KINNAS/319LAB/Applets/Venturi/venturi.html
I am confused (why is static pressure here increase with velocity
increase?).
Thank you for help. Ondrej
Ondrej
I dont know why and how is increasing the static pressure with
increasing velocity(it is logicall, that dynamic pressure grows up, but
why the static one also). Imagine, that you have 1 tube with constant
flow space, and velocity. How can you compute static pressure here? Is
that somehow depending on velocity?
Bruce Scott TOK
The equations of fluid dynamics say that for steady state flow in a tube,
grad (p + V^2/2) = 0
where p is the pressure, V is the flow in the direction of the tube's
axis, and the tube's geometry is supposed to satisfy a/L << 1 with minor
radius a and scale length (for gradients) L.
I'm not sure what you mean by dynamic and static pressure...
The Bernoulli equation you can find by assuming V varies only along the
tube's length, integrating the above equation over the volume of the
tube (convert it to a surface integral), to find
p + V^2/2 = const
The equation of continuity tells you that if the density is constant the
velocity is proportional to the cross section.
Maybe the definition of dynamic pressure is actually p + V^2/2 ?
--
cu,
Bruce
drift wave turbulence: http://www.rzg.mpg.de/~bds/
Rogier
then according to Bernoulli (with the proper assumptions):
P_reservoir = P_inf = P_static + P_dynamic = P + 0.5 * rho * V^2
Because P_inf is constant P_static varies with V.