Determining shockwave location in Ansys

Transonic · March 25, 2023, 05:39

Hi, is it possible to determine the shockwave location in Ansys fluent please?

What I wanted to know was where along the chord length of an aerofoil, the shockwave is like this graph has done

Thanks in advance

NickFL · March 27, 2023, 06:05

Across a shock wave we will have a sharp change in pressure, velocity, density, etc. We can use that to guide us where the shock location "is".

Transonic · March 27, 2023, 11:22

Hi, so it be correct to just make a pressure plot over the surface, then where the pressure starts to jump, is where the shockwave begins?

NickFL · March 27, 2023, 15:14

Yes that would be one way. Perhaps a more elegant way would be to plot the derivative of the pressure. Where this is a maximum, that would give you the location of the shock. Are you looking at 2D or 3D flow?

Transonic · March 27, 2023, 15:39

Hi Nick, I’ll give that a shot, I’ve never thought about it like that. Would I be plotting that over the aerofoil please?

2-D transonic flow

NickFL · March 28, 2023, 03:27

I am not sure exactly on what type of solution you are attempting. But keep in mind that depending on the airfoil, Mach Number, and angle of attack there can be multiple "correct" solutions. See: https://www.researchgate.net/publica..._Flow_Equation

Transonic · March 28, 2023, 09:49

Quote:

Originally Posted by NickFL

Yes that would be one way. Perhaps a more elegant way would be to plot the derivative of the pressure. Where this is a maximum, that would give you the location of the shock. Are you looking at 2D or 3D flow?

Hi Nick, I couldn’t find the pressure derivative?

NickFL · March 29, 2023, 04:02

Really? Sorry! I would have expected Fluent to include the gradient of pressure in as a post-processing quanitity by now. I would have expected that since the gradient is computed for the mesh adaption it could be accessed. Silly me for assuming anything.

You can create a post-processing scalar variable using a UDF. The UDF does not need to be run during the solution, only when looking at the results. There is a great example in the UDF guide where they create a UDS (user-defined scalar) for the gradient of T^4 (radiation problem). You could easily adapt that.

Edit: See example 8.5.2.1 here: https://ansyshelp.ansys.com/account/...ampleUDFs.html

Transonic · March 29, 2023, 10:22

Hi Nick, no problem! Yeah, I thought I had seen it too somewhere and thanks for the link, I’ll take a look!

March 27, 2023, 06:05		#2
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	Across a shock wave we will have a sharp change in pressure, velocity, density, etc. We can use that to guide us where the shock location "is". Transonic likes this.

March 27, 2023, 15:14		#4
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	Yes that would be one way. Perhaps a more elegant way would be to plot the derivative of the pressure. Where this is a maximum, that would give you the location of the shock. Are you looking at 2D or 3D flow? Transonic likes this.

March 28, 2023, 03:27		#6
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	I am not sure exactly on what type of solution you are attempting. But keep in mind that depending on the airfoil, Mach Number, and angle of attack there can be multiple "correct" solutions. See: https://www.researchgate.net/publica..._Flow_Equation Transonic likes this.

March 29, 2023, 04:02		#8
NickFL Senior Member Join Date: Jun 2009 Location: Technische Universität Chemnitz Posts: 107 Rep Power: 17	Really? Sorry! I would have expected Fluent to include the gradient of pressure in as a post-processing quanitity by now. I would have expected that since the gradient is computed for the mesh adaption it could be accessed. Silly me for assuming anything. You can create a post-processing scalar variable using a UDF. The UDF does not need to be run during the solution, only when looking at the results. There is a great example in the UDF guide where they create a UDS (user-defined scalar) for the gradient of T^4 (radiation problem). You could easily adapt that. Edit: See example 8.5.2.1 here: https://ansyshelp.ansys.com/account/...ampleUDFs.html Transonic likes this.

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March 27, 2023, 11:22		#3
Transonic Member Join Date: Jan 2023 Posts: 32 Rep Power: 3	Hi, so it be correct to just make a pressure plot over the surface, then where the pressure starts to jump, is where the shockwave begins?

March 27, 2023, 15:39		#5
Transonic Member Join Date: Jan 2023 Posts: 32 Rep Power: 3	Hi Nick, I’ll give that a shot, I’ve never thought about it like that. Would I be plotting that over the aerofoil please? 2-D transonic flow

March 29, 2023, 10:22		#9
Transonic Member Join Date: Jan 2023 Posts: 32 Rep Power: 3	Hi Nick, no problem! Yeah, I thought I had seen it too somewhere and thanks for the link, I’ll take a look!