Time step unsteady nozzle flow, impingement on plate

taillanm · February 24, 2017, 05:56

Hello everyone,

I am modeling a nozzle flow impinging on a plate (about 1m away from the nozzle exit), and I would like to monitor the pressure on my plate. (Pressure in the chamber: 90bar, Mach at exit around 3)

Since I'm new to unsteady simulations I'ld like to know if anyone has a good rule of thumb to select the time step + number of inner iterations for such a case.

lcarasik · February 24, 2017, 10:41

Quote:

Originally Posted by taillanm

Hello everyone,

I am modeling a nozzle flow impinging on a plate (about 1m away from the nozzle exit), and I would like to monitor the pressure on my plate. (Pressure in the chamber: 90bar, Mach at exit around 3)

Since I'm new to unsteady simulations I'ld like to know if anyone has a good rule of thumb to select the time step + number of inner iterations for such a case.

You should look into reports and monitors in the user manual. These can be used to gather information per time step or iteration that can be reported as a plot and/or reported at Run time with your residuals.

I highly recommend you look into what the CFL (Courant number) number is. This is a basic quantity used for stability of numerical methods and is not meant to be a randomly selected number.

Also, I do not believe Star-CCM+ can handle mach flows.

Edit: Apparently Star-CCM+ Can handle higher (supersonic and transitional flows). My apologies.

taillanm · February 24, 2017, 10:51

Hi, thanks for the reply
what i meant with mach at exit is just an indication, and not some value I would use for some boundary condition (i use a stagnation inlet)

taillanm · March 6, 2017, 07:28

Hi,

I know that it takes about 10ms to reach my total pressure in the chamber, I will linearly go from 0 to 90bar in 10ms. Is a time step smaller than 1ms necessary?

Cheers

me3840 · March 7, 2017, 09:07

STAR-CCM+ is perfectly capable of simulating high-mach flows.

Why are you ramping up the inlet pressure? Are you interested in the formation of the jet or only what the jet does after it's formed?

As Icarasik said you need to look into the CFL number, it will inform you how big you should make your timestep. However you don't have to make it exactly 1, since this is implicit.

February 24, 2017, 05:56	Time step unsteady nozzle flow, impingement on plate	#1
taillanm Member Join Date: Nov 2015 Posts: 57 Rep Power: 10	Hello everyone, I am modeling a nozzle flow impinging on a plate (about 1m away from the nozzle exit), and I would like to monitor the pressure on my plate. (Pressure in the chamber: 90bar, Mach at exit around 3) Since I'm new to unsteady simulations I'ld like to know if anyone has a good rule of thumb to select the time step + number of inner iterations for such a case.

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February 24, 2017, 10:51		#3
taillanm Member Join Date: Nov 2015 Posts: 57 Rep Power: 10	Hi, thanks for the reply what i meant with mach at exit is just an indication, and not some value I would use for some boundary condition (i use a stagnation inlet)

March 6, 2017, 07:28		#4
taillanm Member Join Date: Nov 2015 Posts: 57 Rep Power: 10	Hi, I know that it takes about 10ms to reach my total pressure in the chamber, I will linearly go from 0 to 90bar in 10ms. Is a time step smaller than 1ms necessary? Cheers

March 7, 2017, 09:07		#5
me3840 Senior Member Join Date: Nov 2010 Location: USA Posts: 1,232 Rep Power: 24	STAR-CCM+ is perfectly capable of simulating high-mach flows. Why are you ramping up the inlet pressure? Are you interested in the formation of the jet or only what the jet does after it's formed? As Icarasik said you need to look into the CFL number, it will inform you how big you should make your timestep. However you don't have to make it exactly 1, since this is implicit.