Learning Forum

[Subho]

In discrete phase modeling mass in domain is possible in DPM report definition . Can we check flow rate (mass or volume) at particular location in domain may be at particular point or plane? I have found for fluid we can calculate mass or volume flow rate at particular point or plane in results section but not finding anything for particle.n

[subhamdas]

Fluent allows you to calculate DPM concentration(kg/m3). You can write an expression to derive the flow rate of the particle from its concentrationn

[DrAmine]

You can sample the particles along that boundary or plane or if its domain boundary you can write a DPM boundary UDF and do summing the flow rates. n

[Subho]

Dear thanks for your suggestion. It might be helpful for my case but unfortunately, I am not getting DPM Concentration variable in Discrete Phase Variables category. The variables which I am getting in this category are DPM Wall X Force, DPM Wall Y Force, DPM Wall Z Force and DPM Wall Normal Pressure. For Discrete Phase modelling I have created injectors which is injecting from surface with a particular velocity (normal to surface) and mass flow rate for transient case. I have run this case with single injector and steady case but still not getting DPM Concentration variable. Can you please guide me what I am missing in this case?nThanks in advancenn

[Subho]

Dear thanks for your suggestion. You have suggested a very good option which was beyond of my knowledge. I have tried this and got one *.dpm file which contain value of x, y, z, u, v, w, diameter, t, mass-flow, mass, frequency, time and name. I suppose the unit of values used here is the unit which I have defined in fluent case setup, x, y, z are the co ordinate of the point where values are calculated, u, v, w are velocity in x, y, z direction in x, y, z points, diameter, mass-flow, mass are diameter, flow rate and mass at that point. But I am not understanding what is t, time and frequency. Can you please explain these three terms?Actually, in my current simulation I am trying to measure concentration of particle in various location inside domain in various time. But I am not getting any direct parameter in my case so I was trying in another way through flow rate. For Discrete Phase modelling I have created injectors which is injecting from surface with a particular velocity (normal to surface) and mass flow rate for transient case. In post processing I am not getting DPM Concentration variable in Discrete Phase Variables category. The variables which I am getting in this category are DPM Wall X Force, DPM Wall Y Force, DPM Wall Z Force and DPM Wall Normal Pressure. Can you suggest on it?.If I want to calculate concentration, I guess mass which I am getting from *.dpm file may be used as mass at particular point, but from where I will get volume. Is there any way to get it?nThanks in advance

[Rob]

Turn on coupled DPM (interaction with continuous phase) and run the model on. You'll then see DPM Concentration. nRegarding the units, look in the Injection file section of the manual: all input/output files from Fluent are SI. n

[Subho]

turning on coupled DPM is showing DPM concentration. But I am not finding for which injector the concentration is showing if I am using more than one injector. nMay we get concentration from sample file (*.dpm file). we are getting property for every injector and at any location in that file. Can we measure volume to calculate concentration from the mass values generating in *.dpm fie. n

[Rob]

It won't, the report is DPM Concentration and not sorted by injection. nThe .dpm file contains the particle location, but not the cell data as the particles are tracked in the Lagrangian reference frame, not the Euler like the flow field. Switching to coupled DPM costs cpu but links the two more closely. nWhat do you actually need to know? n

[Subho]

I actually need to know concentration of every injector with respect of time at a particular location inside the domain. Every injector has different mass flow rate.I was checking in .dpm file it contains mass with respect to time for different injectors in different location. So i thought it may be helpful to find concentration for every injectors at a particular location with respect to time .n

[DrAmine]

The units are kg/s for flow rate and kg for mass.n

[Rob]

You may be able to do it with a DPM output UDF, but it'll be a fair bit of work for (possibly) little gain. n

[DrAmine]

What kind of concentration are you requiring? Relative to what? The Sampling provide particle sensitive information, DPM Concentration is not what you want? so what do you need? What is the boundary condition used for DPM at these boundaries?n

[Subho]

I have tried to do it with DPM output UDF and for that I tried to form a function for concentration = mass at certain point divided by cell volume at particular location. But while doing so I am not availing to find cell volume at that location. I want to confirm is the same thing you also suggesting. If so then how to find cell volume or volume to find concentration at particular location, if no please suggest . n

[Subho]

I am trying to simulate concentration of particle inside fluid domain. In simple was it is an air pollution scenario where various size of particle with various mass flow rate are injecting from surface and spreading inside fluid domain. There will be filters which will absorb particles and other walls also trap particles. So amount of particles will get reduced in various point inside domain. I am trying to see mass of particle over volume of fluid or other term concentration of particle inside fluid. For DPM I have introduced added inert particles with different mass flow rates and different diameters injecting from surface to fluid domain. In fluid (air) domain filters are present and other wall surfaces trap particles. So particle concentration (mass of particle over volume of fluid) will vary in different location. For seeing this concentration I am getting mass of particle at various location from sampling but not getting fluid volume associated with it so that I can divide mass to volume to get concentration. n

[Rob]

It was but now you'e explained what you're doing it's not necessarily correct. If you have one particle in a big cell, and an identical one in a small cell what will the two concentrations be? What implication will that have on your results? n

[Subho]

now I am not going any interaction or complexity regarding particles. In simple way I am getting mass of particle at particle location through sampling. In the same way if we get volume then I think we can get concentration at that particular location.What I have understood from sampling is that it is calculating property i.e. mass or flow rate e.t.c in a particular grid or at an element on that location. So can we get the volume of element at that location in fluent or mesh module?n

[DrAmine]

At boundary you cannot get any volume information as it is 2D boundary. Concentration is only available in volumes and as Rob highlighted strong mesh dependency here. You enable Mean Values under DPM Panbel and you might access some other mean variable like mean number of particles /parcels in a cell or mean volume fraction. You can use that to quantify your concentration. Bear in mind the mean values are cell values container of residence time weighted contribution of all particles which passed through a cell and I do not like the values when I am on a boundary. Here I always use use the information from Sampling or the for the DPM Extended Summary.n

[Rob]

The particle is tracked in the Lagrangian reference frame, and the mesh is stored (for the flow) on the Eulerian reference frame. So, for a particle location it doesn't need to know about the cell volume. The cell data for a position can be found, but it's non-trivial. nDo the particles alter the flow?n

[Subho]

I am not using exactly at boundary, I am using near boundary or inside the domain where volume elements are present. I want to see concentration for every injector so I think sampling will be good enough process. I just want to know what will be the volume of element for a particular position.n

[Subho]

For my case particle is not reacting with fluid it is only flowing with fluid. Inside fluid one porous medium is present which is defined by internal and viscous resistance and particle will be trapped at boundary wall. This simple case I am going to set. nCan you guide me how to find cell data for a position, let it be non trivial. I want to know volume of cell for a particular position. n

[DrAmine]

Volume of cell is a variable you can access it n

[Subho]

Can you please guide me how to get volume of cell variable in a particular position. I am finding but not getting it. Is it in fluent or in mesh module ?n

[mraz]

nDid you figure out the solution. I also want to plot number concentration (or mass concentration) at particular location in domain over time. Would you please share with me if you find how to do it. nThanks, n

[Rob]

You want a monitor point: look at the Report Definitions in the tutorials for examples (click on Help to access). n

[DrAmine]

Create a point create vertex average of the variable you want to monitor and enable report plotn