Hypersonic flow over double wedge

marilyn · April 19, 2013, 15:41

Hi! I want to analyze the shock interactions in a hypersonic flow over a double wedge. My Mach number is 9. I generated an unstructured mesh with about 2lakh elements. I chose such a large number because my instructor says that the mesh has to be very refined for such flows.I am new to CFD and Fluent and I am not sure in how many iterations my solution should converge. I set the residuals to 1e-5. Even after about 80000 iterations, the residual was still at 1e-2. Is this natural or am I doing something wrong? Also, how long do these computations usually take? Please help. Thanks a lot.

diamondx · April 19, 2013, 15:55

A not converged solution can be caused by various setting ? probably your mesh, probably you boundary conditions. have you followed any tutorial before ?

marilyn · April 19, 2013, 16:34

Quote:

Originally Posted by diamondx

A not converged solution can be caused by various setting ? probably your mesh, probably you boundary conditions. have you followed any tutorial before ?

I could not get any tutorial specific to double wedge flow problems. But, I followed a tutorial on supersonic flow over a wedge. I think my boundary conditions are also right. I have set the wedges to wall boundary condition, otlet to pressure outlet and the farfield boundary to pressure farfield. As far as the mesh is concerned, I perform the grid check operation whenever I start the simulation. It has never shown any error.

diamondx · April 19, 2013, 16:50

good, how about your mesh ? are working in 3d or 2D ?? structured or unstructured ? i have work with supersonic flow, they are very very difficult to converge, did you run the simulation with 1st order then switched to second ?

marilyn · April 19, 2013, 16:56

Quote:

Originally Posted by diamondx

good, how about your mesh ? are working in 3d or 2D ?? structured or unstructured ? i have work with supersonic flow, they are very very difficult to converge, did you run the simulation with 1st order then switched to second ?

It is a 2D mesh. and a very simple geometry. It is an unstructured mesh with local refining around a vertex. I directly ran it in the second order.

diamondx · April 19, 2013, 17:04

deciding what order should depend on the nature of the flow, and not the simplicity of the geometry. hypersonic should be difficult to predict. i suggest you start with a density based, first order see what you get...

marilyn · April 19, 2013, 17:07

Quote:

Originally Posted by diamondx

deciding what order should depend on the nature of the flow, and not the simplicity of the geometry. hypersonic should be difficult to predict. i suggest you start with a density based, first order see what you get...

shall try doing that and see what happens. thanks a lot for your help

Far · April 20, 2013, 14:26

https://confluence.cornell.edu/displ...+Specification

https://confluence.cornell.edu/displ...w+Over+a+Wedge

April 19, 2013, 15:41	Hypersonic flow over double wedge	#1
marilyn New Member Join Date: Apr 2013 Posts: 5 Rep Power: 13	Hi! I want to analyze the shock interactions in a hypersonic flow over a double wedge. My Mach number is 9. I generated an unstructured mesh with about 2lakh elements. I chose such a large number because my instructor says that the mesh has to be very refined for such flows.I am new to CFD and Fluent and I am not sure in how many iterations my solution should converge. I set the residuals to 1e-5. Even after about 80000 iterations, the residual was still at 1e-2. Is this natural or am I doing something wrong? Also, how long do these computations usually take? Please help. Thanks a lot.

April 19, 2013, 15:55		#2
diamondx Super Moderator Ghazlani M. Ali Join Date: May 2011 Location: Tokyo, Japan Posts: 1,385 Blog Entries: 23 Rep Power: 28	A not converged solution can be caused by various setting ? probably your mesh, probably you boundary conditions. have you followed any tutorial before ? __________________ Regards, New to ICEM CFD, try this document --> https://goo.gl/KAOIwm Ali

April 19, 2013, 16:50		#4
diamondx Super Moderator Ghazlani M. Ali Join Date: May 2011 Location: Tokyo, Japan Posts: 1,385 Blog Entries: 23 Rep Power: 28	good, how about your mesh ? are working in 3d or 2D ?? structured or unstructured ? i have work with supersonic flow, they are very very difficult to converge, did you run the simulation with 1st order then switched to second ? __________________ Regards, New to ICEM CFD, try this document --> https://goo.gl/KAOIwm Ali

April 19, 2013, 17:04		#6
diamondx Super Moderator Ghazlani M. Ali Join Date: May 2011 Location: Tokyo, Japan Posts: 1,385 Blog Entries: 23 Rep Power: 28	deciding what order should depend on the nature of the flow, and not the simplicity of the geometry. hypersonic should be difficult to predict. i suggest you start with a density based, first order see what you get... __________________ Regards, New to ICEM CFD, try this document --> https://goo.gl/KAOIwm Ali

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