CFD Online Discussion Forums

CFD Online Discussion Forums - CFX http://www.cfd-online.com/Forums/ en Thu, 09 Sep 2010 08:40:09 GMT vBulletin 60 http://www.cfd-online.com/Forums/images/misc/rss.jpg CFD Online Discussion Forums - CFX http://www.cfd-online.com/Forums/ Energy Domain Imbalances for Multiphase flow http://www.cfd-online.com/Forums/cfx/79925-energy-domain-imbalances-multiphase-flow.html Wed, 08 Sep 2010 15:58:09 GMT Hi, I am performing a multiphase simulation with 2 phases, an oil and a gas. It is set up with the Homogenous Eulerian-Eulerian model. There is... Hi,

I am performing a multiphase simulation with 2 phases, an oil and a gas.
It is set up with the Homogenous Eulerian-Eulerian model. There is no interphase mass transfer.
I am solving for Total Energy as the viscous work needs to be included. The homogenous heat transfer model is used.

My simulation runs with no problem and the residuals converge below 1e-6.
The Domain Imbalances are below 1% for all variables except the Energy-equation for the two phases. Both show considerable imbalances in the range 20 to 100 %.

I have noticed that the actual value of the imbalances are very close and I suspect the imbalances are simply the transfer of energy from one phase to another.
The CFX manual states that for the Homongenous Heat transfer model the solver "solves a separate enthalpy equation for each fluid with a large interphase heat transfer term which forces the temperature fields to be the same". This fits with my assumption regarding the imbalance.

However I have been unable to find anything in the manual (or elsewhere) to confirm my assumption, i.e. that this Imbalance can be ignored if and conservation is upheld as long as the actual values of the energy imbalances are the same.

Any help is appreciated.

/KMJ ]]> CFX KMJ http://www.cfd-online.com/Forums/cfx/79925-energy-domain-imbalances-multiphase-flow.html Particle User Source in ANSYS CFX http://www.cfd-online.com/Forums/cfx/79916-particle-user-source-ansys-cfx.html Wed, 08 Sep 2010 13:28:57 GMT Hi All:

Lagrange Particle Transport Tracking is used in my simulation.

I am trying to use "Particle User Source" to add momentum source to particle tracking. At the Domain -> Fluid Pair Models-> Particle User Source, in the Arguments list, the "Electric Field" is not available. Does it mean "Electric Field" can not be used as an argument for the "Particle User Source"? Or is there another way to use "Electric Field" as one argument?

Thank you very much for your help. ]]> CFX Jun http://www.cfd-online.com/Forums/cfx/79916-particle-user-source-ansys-cfx.html <![CDATA[[CFD-Post] Using data from inserting a plane]]> http://www.cfd-online.com/Forums/cfx/79914-cfd-post-using-data-inserting-plane.html Wed, 08 Sep 2010 12:48:09 GMT Hi, Is it possible to obtain data on a plane which is inserted using the Location Submenu? In particular, when a plane slices a mesh tetra... Hi,

Is it possible to obtain data on a plane which is inserted using the Location Submenu? In particular, when a plane slices a mesh tetra element a triangle is formed on the plane. It is data at the nodes and centroid of this triangle that I'd like to use. The data is velocity components and Cartesian co-ordinates.

Also, is it possible to make a plane which has a specified area less than the extent of the domain boundaries? For example, if I have a cube shaped domain of 1m by 1m by 1m could I have a plane of size 0.1m by 0.1m? I've not had any luck in my attempts.

The reason for wanting these two features is to use the drag decomposition wake integration method detailed in the journal paper [1] to calculate the induced, profile and wave drag components of an aircraft. The induced drag is of most interest to me. Where as the forces in CFD-Post will only give pressure and shear stress suface integrated components.

Thanks,

[1], Giles & Cummings, Wake Integration for 3-D Flowfield Computations: Theoretical Development, Journal of Aircraft, Vol. 36, No. 2, March-April, 1999. ]]> CFX siw http://www.cfd-online.com/Forums/cfx/79914-cfd-post-using-data-inserting-plane.html gas diffusion through membrane http://www.cfd-online.com/Forums/cfx/79911-gas-diffusion-through-membrane.html Wed, 08 Sep 2010 12:14:33 GMT Lets say we have a box where there is a source of gas CO2 (at the bottom) and it is shut by a membrane (top). The box with the membrane is in... Lets say we have a box where there is a source of gas CO2 (at the bottom) and it is shut by a membrane (top). The box with the membrane is in atmospheric environment (simplest case). I want to simulate in CFX the diffusion through the membrane and finally find out the mass fractions of the air and CO2 inside the box.

I create two domains: the bottle without the membrane and the membrane itself. The first one is a fluid domain defined to contain a mixture of air (constraint) and CO2 with the kinematic diffusivity of CO2 in air.

What i did was to define the membrane domain as fluid domain containing again the CO2 and Air(constraint) mixture but with different kinematic viscocity.

There is a common area (between box domain and membrane domain) though that i do not know whether to define as a boundary or as an interphase (i did it as an interphase and the solution has errors - i get no results)

Any help on this?

What type of domain should i define the membrane?

If solid then i can not find a way to insert the diffusion coefficient of the membrane interacting with the mixture ]]> CFX sosat1012 http://www.cfd-online.com/Forums/cfx/79911-gas-diffusion-through-membrane.html parallel and multiphase http://www.cfd-online.com/Forums/cfx/79908-parallel-multiphase.html Wed, 08 Sep 2010 11:24:15 GMT hello,
i have a problem,
my calculation on 4 cpu's differs two much from this on 8 cpu's with the same setup? what did go wrong? (multiphase flow) ]]> CFX Zaktatir http://www.cfd-online.com/Forums/cfx/79908-parallel-multiphase.html Double Precision Override http://www.cfd-online.com/Forums/cfx/79897-double-precision-override.html Wed, 08 Sep 2010 08:00:16 GMT Can someone explain the meaning of this override option??.. The difference between it and the normal double precision at the run tab Can someone explain the meaning of this override option??.. The difference between it and the normal double precision at the run tab ]]> CFX Zaktatir http://www.cfd-online.com/Forums/cfx/79897-double-precision-override.html Sources in Multiphase Flow http://www.cfd-online.com/Forums/cfx/79896-sources-multiphase-flow.html Wed, 08 Sep 2010 07:41:40 GMT Hello everyone, I am trying to model a mixing tank with the following materials and components: Material 1: Air (gas, dispersed fluid)... Hello everyone,

I am trying to model a mixing tank with the following materials and components:

Material 1: Air (gas, dispersed fluid)
Material 2: AirWaterMixture (liquid, continuous fluid) with two components
Component 1: Air (transport equation)
Component 2: Water (constraint)

I am trying to model the transfer of gas Air (Material 1) to dissolved Air (Material 2.Component 1) with the following source term:

DOSource = K1*(dens)*(C1+0.001*C0-(AirWaterMixture.Air.mf))

where K1, dens, C1 and C0 are constants. I don't get any error when I define the problem, but when I start the solver, in the first iteration I get the following error message:

| ERROR #001100279 has occurred in subroutine ErrAction.
| Message:
| NAME_MOD: Error finding variable "MASFRN_FL1_FL2"

I have been trying different things, but none of them work. Surprisingly, if I define the source term as:

DOSource = K1*(dens)*(C1+0.001*C0-(Air.vf))

I don't get any error, but this is not the correct definition of the source term.

Does anyone have any clue about what it causing this error? Or about any other way of modelling the transfer of Air in gas phase to dissolved Air in liquid phase?

Many thanks for your help, ]]> CFX lcea http://www.cfd-online.com/Forums/cfx/79896-sources-multiphase-flow.html Near Wall Turbulence in CFX http://www.cfd-online.com/Forums/cfx/79885-near-wall-turbulence-cfx.html Tue, 07 Sep 2010 16:24:47 GMT Hey guys, just a few quick questions about CFX and turbulence models in general. I am trying to compare the efficiency of wall functions vs.... Hey guys, just a few quick questions about CFX and turbulence models in general.

I am trying to compare the efficiency of wall functions vs. integration to the wall. I have studied up a fair amount on this but sadly my understanding of the material is low.

I am running a simulation of a sharp-edged object around mach 6, and so far i have tried running the k-w turbulence model, the BSL (which is also based on the k-omega model - correct? just multiplied by some factors) and the SAS SST model (again, based on the k-omega model, am I right, except it takes into account the turbulent shear stress).

Now these "omega-based" models have an automatic near-wall treatment as opposed to a scalable wall function treatment. This is where I am confused.
How do I go about simply integrating to the wall instead of using a wall function? There doesn't seem to be an option for that. The closest thing seems to be an automatic near-wall treatment - which still doesn't allow me to choose whether I want to use a full integration to the wall approach or a wall function approach.

Can someone clarify this to me? How do I integrate to the wall using these turbulence models?

Thanks very much in advance. ]]> CFX pawan1989 http://www.cfd-online.com/Forums/cfx/79885-near-wall-turbulence-cfx.html Wave amplitude problem http://www.cfd-online.com/Forums/cfx/79870-wave-amplitude-problem.html Tue, 07 Sep 2010 10:33:40 GMT Hi everyone, I need the aid of the experts. I´m simulating a water tank as a wave generator. I have calculated the wave amplitude at... Hi everyone,

I need the aid of the experts.

I´m simulating a water tank as a wave generator.
I have calculated the wave amplitude at different planes (0.5m, 1.5m, 2.75m from the entrance) and:

1. It´s lower than it should (it should be 1,65m high)

2. It´s lower as the plane is far away from the entrance

COuld anyone advise me, please??? Could it be the mesh, the advection scheme, the turbulence????

Thanks in advance

Attached Images

	planes.jpg (23.0 KB)
	Amplitud_escalasinpile.jpg (69.1 KB)

Attached Files

This run of the CFX.doc (78.5 KB)

]]> CFX cfxmar http://www.cfd-online.com/Forums/cfx/79870-wave-amplitude-problem.html Symmetry in CHT problem http://www.cfd-online.com/Forums/cfx/79867-symmetry-cht-problem.html Tue, 07 Sep 2010 10:02:49 GMT Good morning, I am trying to model a half - symmetric CHT problem with one fluid domain and multiple solid domains. Do I have to make multiple... Good morning,

I am trying to model a half - symmetric CHT problem with one fluid domain and multiple solid domains.

Do I have to make multiple symmetric boundary conditions (1 for the fluid domain and one for every other solid domains) ?

When i set total source power for the solid subdomains do i have to input the real power or just half of it because the half symmetry of the model ?

Thank you in advance,

Costin Ruja ]]> CFX costinruja http://www.cfd-online.com/Forums/cfx/79867-symmetry-cht-problem.html convergence problem in the turbomachinery problem. http://www.cfd-online.com/Forums/cfx/79854-convergence-problem-turbomachinery-problem.html Tue, 07 Sep 2010 06:07:17 GMT what are the issue for the convergence of a simulation. In my case I am solving a centrifugal fan problem. In which I am simulating the impeller as... what are the issue for the convergence of a simulation. In my case I am solving a centrifugal fan problem. In which I am simulating the impeller as well as the volute. I imposed the boundary conditions at
1) inlet : total pressure (0 pa relative pressure)
2) Outlet : mass flow rate:
3) impeller : Rotating wall;
4) casing :stationary wall;
I am using the k- omega turbulence model for solving the turbulent quantities.
I set the convergence criteria as 10e-4 for the velocities and the turbulence quantities.
I am solving the momentum equations with High resolution scheme.
I got struck when the simulation is not conversing up to the 10e-4. but I want it must touch the criteria of the 10e-5.
Can anyone help me where may be the problem? Please suggest me. Thank you. ]]> CFX u k jha http://www.cfd-online.com/Forums/cfx/79854-convergence-problem-turbomachinery-problem.html Does any1 have tutorial related to Re-meshing in CFX ??? http://www.cfd-online.com/Forums/cfx/79852-does-any1-have-tutorial-related-re-meshing-cfx.html Mon, 06 Sep 2010 17:21:40 GMT I have contacted the customer service but haven't heard from them. Does anyone have the ANSYS Re-meshing tutorial or any document related to Re-meshing ???

Thank you,

Eric. ]]> CFX vmlxb6 http://www.cfd-online.com/Forums/cfx/79852-does-any1-have-tutorial-related-re-meshing-cfx.html multiphase cavitation http://www.cfd-online.com/Forums/cfx/79844-multiphase-cavitation.html Mon, 06 Sep 2010 14:01:25 GMT Hi all, I want to know if CFX is capable to model free surface cavitation in multiphase condition (air ,water and vapor). I am looking for your... Hi all,
I want to know if CFX is capable to model free surface cavitation in multiphase condition (air ,water and vapor). I am looking for your advise. thanks. ]]> CFX fth http://www.cfd-online.com/Forums/cfx/79844-multiphase-cavitation.html local time step http://www.cfd-online.com/Forums/cfx/79838-local-time-step.html Mon, 06 Sep 2010 10:47:53 GMT Hello.

I'm doing a calculation which simulates a steam turbine diffuser.
I generally use a local time step which I gradually increase from 1 to 50.
This is generally okay for most of my cases.

However, for some outlet boundary conditions, the calculation does not converge and the flow separates significantly.
When I have these cases, I can often (not always!) make the solution converged by increasing the local time step to a very large number (say 200)

I wonder what this means.
Does it mean that my actual time step (delta t) is increased significantly and misses small time scale fluctuations?

Kind Regards, ]]> CFX syoon http://www.cfd-online.com/Forums/cfx/79838-local-time-step.html Re-meshing in CFX http://www.cfd-online.com/Forums/cfx/79835-re-meshing-cfx.html Mon, 06 Sep 2010 09:19:43 GMT Can somebody guide me through the procedure of re-meshing in CFX for Dynamic mesh simulations. Is there any tutorial available for the same ??? ... Can somebody guide me through the procedure of re-meshing in CFX for Dynamic mesh simulations.

Is there any tutorial available for the same ???

Thank you very much. ]]> CFX vmlxb6 http://www.cfd-online.com/Forums/cfx/79835-re-meshing-cfx.html