Residuals?

Rav_G · October 15, 2014, 08:38

Hello all, first of all I'm a newbie to CFD and I'm currently doing a placement at a n engineering company so the question I'm going to ask might seem stupid as it is a very basic question but I thought this is the best place to ask it rather than asking the experts in my office and looking like an idiot (I probably do here anyway but you lot seem like a nice bunch

).

So the CFD software (can't really mention what it is) outputs a residual file with values for different variables. My problem is, I don't exactly know which variable represents what. So if anyone can shed some light on this very basic (rather stupid) question I would be very greatful! The variables are:

Rho
Rho U
Rho V
Rho W
Rho E
Rho K
Rho Omega

and some forces but I know what they are.

Again, thank you very much!

Alex C. · October 15, 2014, 09:31

A quick look at the software manual should help you on this.

rho most likely stands for fluid density

then everything other variables is multiplied by rho.

U, V and W are typically the velocities in the X,Y and Z axis, respectively.
E is probably the internal energy.
K and Omega are turbulence model variables.

All these variables are subject to different normalization that are software specific. As previously stated : the user manual is your best friend for this kind of things. If you don't have access to this manual, go and see experts from the office, they probably think it is weird you didn't ask already.

cfdnewbie · October 15, 2014, 11:42

These are the conserved variables in compressible Navier-Stokes with a k/epsilon RANS model.

Rav_G · October 16, 2014, 04:58

Thanks all!

Seth.Prashant · October 17, 2014, 07:55

With so many occurrences of rho, I have a hunch it does not mean the density.

Are you sure it is not the partial derivative operator? In which case each of the variables you have listed (Rho U, Rho V, Rho W,...Rho Omega) will be the residuals of the quantities U, V,..etc generated after the solver has solved each iteration step. The solver iterates until these residuals reach the target value, also known as convergence. This is what I would expect seeing in the residual file.

Please feel free to correct me as I am no expert myself.

Thanks!

October 15, 2014, 08:38	Residuals?	#1
Rav_G New Member Join Date: Oct 2014 Posts: 2 Rep Power: 0	Hello all, first of all I'm a newbie to CFD and I'm currently doing a placement at a n engineering company so the question I'm going to ask might seem stupid as it is a very basic question but I thought this is the best place to ask it rather than asking the experts in my office and looking like an idiot (I probably do here anyway but you lot seem like a nice bunch ). So the CFD software (can't really mention what it is) outputs a residual file with values for different variables. My problem is, I don't exactly know which variable represents what. So if anyone can shed some light on this very basic (rather stupid) question I would be very greatful! The variables are: Rho Rho U Rho V Rho W Rho E Rho K Rho Omega and some forces but I know what they are. Again, thank you very much!

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
motorBike Residuals for SST k-omega... and mine	JR22	OpenFOAM Running, Solving & CFD	6	August 1, 2013 09:08
what to monitor besides residuals?	franzdrs	FLUENT	5	March 21, 2013 03:59
judging convergence through residuals	MachZero	Main CFD Forum	7	December 25, 2012 12:18
Strange residuals of the Density Based Solver	Pat84	FLUENT	0	October 22, 2012 15:59
Convergence - scaled vs unscaled residuals	HS	FLUENT	1	November 7, 2005 05:45

October 15, 2014, 09:31		#2
Alex C. Member Join Date: Jul 2013 Posts: 55 Rep Power: 12	A quick look at the software manual should help you on this. rho most likely stands for fluid density then everything other variables is multiplied by rho. U, V and W are typically the velocities in the X,Y and Z axis, respectively. E is probably the internal energy. K and Omega are turbulence model variables. All these variables are subject to different normalization that are software specific. As previously stated : the user manual is your best friend for this kind of things. If you don't have access to this manual, go and see experts from the office, they probably think it is weird you didn't ask already.

October 15, 2014, 11:42		#3
cfdnewbie Senior Member cfdnewbie Join Date: Mar 2010 Posts: 557 Rep Power: 20	These are the conserved variables in compressible Navier-Stokes with a k/epsilon RANS model.

October 16, 2014, 04:58		#4
Rav_G New Member Join Date: Oct 2014 Posts: 2 Rep Power: 0	Thanks all!

October 17, 2014, 07:55		#5
Seth.Prashant New Member Join Date: Oct 2014 Posts: 7 Rep Power: 11	With so many occurrences of rho, I have a hunch it does not mean the density. Are you sure it is not the partial derivative operator? In which case each of the variables you have listed (Rho U, Rho V, Rho W,...Rho Omega) will be the residuals of the quantities U, V,..etc generated after the solver has solved each iteration step. The solver iterates until these residuals reach the target value, also known as convergence. This is what I would expect seeing in the residual file. Please feel free to correct me as I am no expert myself. Thanks!