[jasir.jawad]

I am simulating injection of water droplets into a body of superheated steam. I have noticed in the DPM injections point properties, that the user may specify mass flowrate, velocity and radius as well. If this outer radius is the radius of the injector, then isn't it redundant to specify both the velocity and the radius? Or is the outer radius something completely different?

[alainislas]

According to Ansys Fluent User Manuel, you'll find the following









A nonzero inner radius can be specified to model injectors that do not emanate from a single point. Set the radius (defined as shown in Figure 23.3.4) in the Radius field. The particles will be distributed about the axis with the specified radius.

[jasir.jawad]

Originally Posted by alainislas

According to Ansys Fluent User Manuel, you'll find the following









A nonzero inner radius can be specified to model injectors that do not emanate from a single point. Set the radius (defined as shown in Figure 23.3.4) in the Radius field. The particles will be distributed about the axis with the specified radius.

Thank you for response. I have already looked up fluent guide and help and found the exact same thing. In this case, what if my injection is emanating from a single point? Do I set the radius zero (by default=0.005)? Also is the velocity of the injection then independent of the radius/dia of the injector?

[alainislas]

Yes, I'd set the radius to zero (or a very very small number). Regarding the other question, I don't see a reason to think that there is a dependency between the radius and the velocity of the injection. Why do you think so?


Just be cautious with velocity and mass flow rate, these are independent parameters. Keep in mind that in DPM, the mass flow rate is NOT a continuous mass flow rate (i.e., m_dot = rho*A*velocity is not valid). In DPM, the mass flow rate is discrete, and has nothing to do with the velocity that you input in the setup panel

[jasir.jawad]

Originally Posted by alainislas

Yes, I'd set the radius to zero (or a very very small number). Regarding the other question, I don't see a reason to think that there is a dependency between the radius and the velocity of the injection. Why do you think so?


Just be cautious with velocity and mass flow rate, these are independent parameters. Keep in mind that in DPM, the mass flow rate is NOT a continuous mass flow rate (i.e., m_dot = rho*A*velocity is not valid). In DPM, the mass flow rate is discrete, and has nothing to do with the velocity that you input in the setup panel

Hi Alain. Thank you for the clarification. I assumed (m_dot = rho*A*velocity) should be valid for DPM as well. If your point is valid, then there is no reason to think that the radius and velocity are related. Is there a reference article or guide that can provide for information on this?

I understand that the mass flow is discrete for DPM. The mass is injected at each time step based on the total mass flow rate specified. But in terms of design, it is difficult to understand how to achieve the specified velocity without changing the mass flow rate or the diameter/radius of the injector. Anyway, thank you for your help.

[alainislas]

For the DPM mass flow rate calculation, you can refer to any of my old posts in the Ansys Fluids Forum


https://forum.ansys.com/forums/topic...ion-speed-m-s/


https://forum.ansys.com/forums/topic...tal-flow-rate/


https://forum.ansys.com/forums/topic...les-injection/


https://forum.ansys.com/forums/topic/regarding-dpm-2/

[jasir.jawad]

Originally Posted by alainislas

For the DPM mass flow rate calculation, you can refer to any of my old posts in the Ansys Fluids Forum


https://forum.ansys.com/forums/topic...ion-speed-m-s/


https://forum.ansys.com/forums/topic...tal-flow-rate/


https://forum.ansys.com/forums/topic...les-injection/


https://forum.ansys.com/forums/topic/regarding-dpm-2/

Thank you for the links to old post. It helped a lot to understand the process. Could you confirm, how we can calculate strength (#particles per sec [#/s]) for solid cone injection? Is it the same as the reciprocal of the time step?

I have specified 9 injection points (solid cone injection) each with 60 streams. My timestep is 0.005 s. What will be the #particles/second or number of particles per stream?

[alainislas]

For better assistance, please provide a snapshot of your DPM injection panel