Billboard Analysis - Part 3

(Continuation of Part 2)

Now the following figure is the graph for the relative static pressure.

 

We want to see the relative static pressure distribution around the billboard. Here it is.

 

We can see and predict that the pressure in the left side is lower than in the right side of the billboard. It can be accepted because the velocity magnitude of the left side is higher than the right side. We can see the value of the relative static pressure in the “lihat alfa” menu. The following table is the relative static pressure in the left and right side of the billboard.

J	left side	right side
21	2.47E-01	-4.20E+01
22	1.09E+01	-4.18E+01
23	1.56E+01	-4.14E+01
24	1.86E+01	-4.10E+01
25	2.06E+01	-4.06E+01
26	2.19E+01	-4.02E+01
27	2.28E+01	-3.99E+01
28	2.33E+01	-3.97E+01
29	2.35E+01	-3.95E+01
30	2.35E+01	-3.93E+01
31	2.33E+01	-3.93E+01
32	2.28E+01	-3.92E+01
33	2.21E+01	-3.93E+01
34	2.10E+01	-3.94E+01
35	1.96E+01	-3.96E+01
36	1.77E+01	-4.00E+01
37	1.51E+01	-4.04E+01
38	1.16E+01	-4.09E+01
39	6.34E+00	-4.16E+01
40	-4.56E+00	-4.21E+01
Average	1.68E+01	-4.04E+01

Our prediction is correct. The pressure in left side is lower. The total of the pressure in the left side is in the direction of x positive, while the pressure of the right side is the opposite.

We want to know the force acting on the left and right side of the billboard, this is the table shown the calculation.

J	relative pressure left side (Pa)	relative pressure right side (Pa)	area (m^2)	Force left (N)	Force right (N)
21	2.47E-01	-4.20E+01	1.03E-01	2.56E-02	-4.34E+00
22	1.09E+01	-4.18E+01	1.03E-01	1.13E+00	-4.32E+00
23	1.56E+01	-4.14E+01	1.03E-01	1.61E+00	-4.28E+00
24	1.86E+01	-4.10E+01	1.03E-01	1.92E+00	-4.24E+00
25	2.06E+01	-4.06E+01	1.03E-01	2.13E+00	-4.20E+00
26	2.19E+01	-4.02E+01	1.03E-01	2.27E+00	-4.16E+00
27	2.28E+01	-3.99E+01	1.03E-01	2.36E+00	-4.13E+00
28	2.33E+01	-3.97E+01	1.03E-01	2.41E+00	-4.11E+00
29	2.35E+01	-3.95E+01	1.03E-01	2.43E+00	-4.09E+00
30	2.35E+01	-3.93E+01	1.03E-01	2.43E+00	-4.07E+00
31	2.33E+01	-3.93E+01	1.03E-01	2.41E+00	-4.07E+00
32	2.28E+01	-3.92E+01	1.03E-01	2.36E+00	-4.06E+00
33	2.21E+01	-3.93E+01	1.03E-01	2.29E+00	-4.07E+00
34	2.10E+01	-3.94E+01	1.03E-01	2.17E+00	-4.08E+00
35	1.96E+01	-3.96E+01	1.03E-01	2.03E+00	-4.10E+00
36	1.77E+01	-4.00E+01	1.03E-01	1.83E+00	-4.14E+00
37	1.51E+01	-4.04E+01	1.03E-01	1.56E+00	-4.18E+00
38	1.16E+01	-4.09E+01	1.03E-01	1.20E+00	-4.23E+00
39	6.34E+00	-4.16E+01	1.03E-01	6.56E-01	-4.30E+00
40	-4.56E+00	-4.21E+01	1.03E-01	-4.72E-01	-4.36E+00
Total			2.07E+00	3.48E+01	-8.35E+01
Average	1.68E+01	-4.04E+01		1.74E+00	-4.18E+00

1.       Case 4

This case is simulate like shown in the class course. The domain is the same with the case 1. The difference is the cells setting. For the case 1, the upper and lower cells are outlet and wall, while for the case 4 are symmetry. It’s shown in the following figure.

 

This is the result for the stream function.

 

We can see that there are two similar vortex. It’s can be predicted in many research result and simulation for bluff body. The following picture is the graph of velocity vector.