Can this be considered as Incompressible

Vignesh2508 · May 1, 2017, 08:48

Hello Guys,

I am doing a simulation on a car. My conditions are that the length of the car is 1m. It is a scaled model. The velocity is at 150 m/s. I want to do a steady state simulation. My doubt is that whether this can be considered as incompressible and solved in simpleFoam.

Thanks

Vicky

Joshua14 · May 1, 2017, 09:47

Vicky,

I would advise treating the simulation as compressible. You can always try simpleFoam, but the rule of thumb that I learned was you can only assume incompressible when the velocity is less then Mach 0.3. In your case I calculate Mach 0.425 (Speed of sound is 353 m/s). This would lead me to use a compressible solver.

Joshua

Vignesh2508 · May 1, 2017, 10:22

Yeah i know that it should be less than 0.3 but I am simulating a scaled car. So I want to know if anybody had met with a similar issue

Thanks

Joshua14 · May 1, 2017, 12:03

Vicky,

Then if you are trying to match Reynolds numbers between the full size car and your model, change viscosity and not velocity. This way you will still have incompressible flow but the correct Reynolds number. I have done this before with airfoils and wings.

Joshua

Vignesh2508 · May 1, 2017, 17:53

Joshua,

That's a pretty interesting method. I will try it.

Thanks for your help.

May 1, 2017, 08:48	Can this be considered as Incompressible	#1
Vignesh2508 Member Vignesh Rajendiran Join Date: Aug 2016 Location: Chennai, India Posts: 62 Rep Power: 9	Hello Guys, I am doing a simulation on a car. My conditions are that the length of the car is 1m. It is a scaled model. The velocity is at 150 m/s. I want to do a steady state simulation. My doubt is that whether this can be considered as incompressible and solved in simpleFoam. Thanks Vicky

May 1, 2017, 12:03		#4
Joshua14 Member Joshua Join Date: Dec 2016 Location: St. Louis, Missouri Posts: 91 Rep Power: 9	Vicky, Then if you are trying to match Reynolds numbers between the full size car and your model, change viscosity and not velocity. This way you will still have incompressible flow but the correct Reynolds number. I have done this before with airfoils and wings. Joshua piu58 and Alasir like this.

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May 1, 2017, 09:47		#2
Joshua14 Member Joshua Join Date: Dec 2016 Location: St. Louis, Missouri Posts: 91 Rep Power: 9	Vicky, I would advise treating the simulation as compressible. You can always try simpleFoam, but the rule of thumb that I learned was you can only assume incompressible when the velocity is less then Mach 0.3. In your case I calculate Mach 0.425 (Speed of sound is 353 m/s). This would lead me to use a compressible solver. Joshua

May 1, 2017, 10:22		#3
Vignesh2508 Member Vignesh Rajendiran Join Date: Aug 2016 Location: Chennai, India Posts: 62 Rep Power: 9	Yeah i know that it should be less than 0.3 but I am simulating a scaled car. So I want to know if anybody had met with a similar issue Thanks

May 1, 2017, 17:53		#5
Vignesh2508 Member Vignesh Rajendiran Join Date: Aug 2016 Location: Chennai, India Posts: 62 Rep Power: 9	Joshua, That's a pretty interesting method. I will try it. Thanks for your help.