Labrotary Work 1
Labrotary Work 1
Labrotary Work 1
Department of Aerohydrodynamics
LABORATORY WORK №1
Specific energy of a flowing liquid
Bernoulli’s equation.
Consider a pipe with varying diameter and height through which an
incompressible fluid is flowing. The relationship between the areas of cross-
sections A, the flow speed v, height from the ground y, and pressure p at two
different points 1 and 2 is given in the figure below.
Assumptions:
The density of the incompressible fluid remains constant at both points.
The energy of the fluid is conserved as there are no viscous forces in the
fluid.
Therefore, the work done on the fluid is given as:
dW = F1dx1 – F2dx2
dW = P1A1dx1 – P2A2dx2
dW = P1dV – P2dV = (P1 – P2)dV
The work done on the fluid was due to conservation of gravitational force
and change in kinetic energy. The change in kinetic energy of the fluid is given as:
dK = 0.5m2v22−0.5m1v21=0.5ρdV(v22−v21)
The change in potential energy is given as:
dU = mgy2 – mgy1 = ρdVg(y2 – y1)
Therefore, the energy equation is given as:
dW = dK + dU
(P1 – P2)dV = 0.5ρdV(v22−v21) + ρdVg(y2 – y1)
(P1 – P2) = 0.5ρ(v22−v21) + ρg(y2 – y1)
Rearranging the above equation, we get Bernoulli’s equation:
P1+0.5ρv21+ρgy1=P2+0.5ρv22+ρgy2
Conclusion:
With Bernoulli´s equation we can describe the behavior of a fluid moving
along a streamline, we can observe how the area of the pipe influenced the force
and pressure of the liquid, the velocity and pressure will change their values
according area of pipe and the density of the incompressible fluid remains
constant at both points of the pipe.
Final mark