Point A : L/D2=
0.2 (got backflow at pressure outlet)
Point B : L/D2=
0.35 (no backflow at pressure outlet)
Point C : L/D2= 0.
5 (no backflow at pressure outlet)
Point D : L/D2 = 0.65(no
backflow at pressure outlet)
Point E : L/D2= 0.
8 (no backflow at pressure outlet)
F= L/D2= 0. 95 (no backflow at pressure outlet)
G = L/D2= 1 (no backflow at pressure outlet)
Point H: =
L/D2= 1.15 (no backflow at pressure outlet)
Point I: =
L/D2= 1.3 (no backflow at pressure outlet)
Point J: =
L/D2= 1.45(no backflow at pressure outlet)
Point k: =
L/D2= 1.6(no backflow at pressure outlet)
Point L: =
L/D2= 2(no backflow at pressure outlet)
The best grid
resolution that was chosen in part 1 which is 0.009 min size ,0.04 max face
size and max size. However, with further
investigation at the direction of fluid flow to the pressure outlet.
It is to be found that there is a present of
reverse flow at the pressure outlet when is used the value ratio of L(extend) and
D2 which is 0.2.
With research , it is to be found that in order to avoid
reverse backflow of the fluid at the pressure outlet, one must increase the
ratio of L(extend)/D2. Hence, geometry of L(extend) are then be changed with
the aids of given data of L(extend)/D2. By using contour, the direction of flow
can be observed. The blue color arrow is found to be having the lowest pressure
flow, whereas, the red arrow is the opposite. Reverse backflow usually occurred
at lowest pressure flow.
investigating the backflow of fluid, 12 points have already tested by just keep
changing the L value. It shows that as the L value increase, the point values
also increase when the D2 value is constant. In this case, the only part need
to be focused more is wall surface instead of the diameter region since its
flow field is constant throughout. After all the
trials, in our simulation data, the shortest L(extend) to achieve no backflow
in pressure outlet is 0.35. this is because at this point, value reach
to 0.35 which is point B and its L value is 0.7mm, the backflow region still
can be seen but it start to decrease and become forward flow which is normal
flow in the end, this means that no backflow at pressure outlet.
For this part, 12 point with different L/D2 has been recorded. For this case, the diameter of the P(outlet) is
constant, so the ratio of L/D2 is can be indicated as the change for
Length(extend). The best grid resolution is then be used in part 3 with
different L(extend)/D2. The Pressure(inlet)
and pressure(line8) value was recorded by using the method above from part 2.
The pressure difference was also recorded in the table by using the formula ?P = Pin ? P1(line8). The result was
shown as table above. The percentage error is calculated by using the method
With the aids of the formula, it is to be found that all the
percentage error are relatively low (<5%). From the table above, it can be saw that the L/D2 increase, the P(inlet) increase. But for Pressure(line8), the value was not consistence. It sometimes get a positive value and sometimes get a negative value. For the pressure difference, at the beginning, it starts increase as the L/D2 increase. From the graph, the pressure start to be stable when at the point of 1.3 at x-axis. This means, in order for ?P to become independent of L(extend)/D2, it has to be 1.3. PART 4 L/D2 P(inlet) 0.2 2.61E+06 0.35 2.28E+06 0.5 2.10E+06 0.65 2.03E+06 0.8 2.00E+06 0.95 1.97E+06 1.0 1.93E+06 1.15 1.94E+06 1.3 1.90E+06 1.45 1.88E+06 1.6 1.90E+06 2.0 1.91E+06 For this case, inlet gauge pressure Pin is plotted as a function of Lextend/D2 ratio. It is through collective data that values for each point were accepted and tabulated. The inlet pressure, Pin is independent to the ratio of length / diameter. From the beginning point of 0.2, there are greater drop to the next point in pressure as each Lextend/D2 ratio increases. This unstable trendline happened due to the nature of flow which happens to experience maximum velocity with lower pressure at outlet. As to obey conservation of energy law, compensation was needed for pressure at inlet and pressure at outlet to be balanced. But with each length increase, the flow of fluid becomes more developed, thus reducing the outlet flow velocity and increase the outlet pressure little by little. The flow begins to fully develop upon reaching 1.3, where steady values of pressure input, Pin were observed. In accordance to the above tabulated data, it is recommended to use the diamond highlighted point which valued at 1.3 as the value for ratio Lextend/D2. Beyond this point, too slight difference in percentage error between 1~2% which is considered as stable outcome during recording of data. Convergence hovers at around 1.90 MPa which result to lesser variation in pressure from this point onwards. This fluctuation is insignificant to affect the difference of input pressure, Pin against Lextend/D2 graphical line. Therefore, the Shane chosen was valued at 1.3 ratio for Lextend/D2.