Difference between results of 2D and 3D Analysis

Syed Wajeeh · April 13, 2022, 06:33

Hello all. I am simulating a CD-Bell nozzle and according to the given conditions i.e., pressure ratios, my analytically calculated exit Mach number should be 3.2.
When I run the 2D planar simulation, I get the maximum Mach almost near to the desired value but when I switch to the 3D analysis, the maximum Mach exceeds quite a lot in the center region of the nozzle as can be seen in the attached pictures. However the average Ma at the outlet is nearly identical in both cases i.e.
Also there is a drastic difference between the mass flow rate in both cases and I am unable to understand these differences. Can some one please help me in this regard. Thanks in advance

2D Mach Contour.jpg

2D Mass Flow-rate.JPG

3D Mach Contour.JPG

3D Mass Flow-rate.JPG

Светлана · April 13, 2022, 07:46

Hello, what boundary conditions do you set in 3D simulation? If it is not confidential, would you like to upload your simulation files?

Syed Wajeeh · April 13, 2022, 08:50

Hi Светлана. The file size is almost 1.1GB hence it is not getting uploaded. Inlet pressure = 5.099MPa, Outlet Pressure = 101325Pa, Inlet temp 2780K, Outlet 906K and Adiabatic Walls. Do tell me if you need something else as well. Cheers

April 13, 2022, 06:33	Difference between results of 2D and 3D Analysis	#1
Syed Wajeeh Member Syed Wajeeh Join Date: Mar 2022 Posts: 56 Rep Power: 4	Hello all. I am simulating a CD-Bell nozzle and according to the given conditions i.e., pressure ratios, my analytically calculated exit Mach number should be 3.2. When I run the 2D planar simulation, I get the maximum Mach almost near to the desired value but when I switch to the 3D analysis, the maximum Mach exceeds quite a lot in the center region of the nozzle as can be seen in the attached pictures. However the average Ma at the outlet is nearly identical in both cases i.e. Also there is a drastic difference between the mass flow rate in both cases and I am unable to understand these differences. Can some one please help me in this regard. Thanks in advance 2D Mach Contour.jpg 2D Mass Flow-rate.JPG 3D Mach Contour.JPG 3D Mass Flow-rate.JPG

April 13, 2022, 07:46		#2
Светлана Senior Member Svetlana Tkachenko Join Date: Oct 2013 Location: Australia, Sydney Posts: 407 Rep Power: 14	Hello, what boundary conditions do you set in 3D simulation? If it is not confidential, would you like to upload your simulation files?

April 13, 2022, 08:50		#3
Syed Wajeeh Member Syed Wajeeh Join Date: Mar 2022 Posts: 56 Rep Power: 4	Hi Светлана. The file size is almost 1.1GB hence it is not getting uploaded. Inlet pressure = 5.099MPa, Outlet Pressure = 101325Pa, Inlet temp 2780K, Outlet 906K and Adiabatic Walls. Do tell me if you need something else as well. Cheers