Hello,

I'm a mechanical engineering student and currently I'm working on my final project.

For it I need to simulate the impact of different fluids on the pump, needed power

for a given flow rate and RPM. I'm all new to this simulation thing, all the experiance

I have is from the YouTube tutorials. So far I know how to set the boundary conditions,

rotating regions. The problem starts here: When I put the BC's as enviromental pressure

at inlet and outlet followed by a rotating region at 3000RPM I get a ''vortex crosses the..''

warning message that I can't get rid of. I tried to extend the inlet and outlet pipe but to

no avail and even refined the mesh. When inspecting the surface parameters of inlet and outlet

lid for mass flow rate I get a different reading but in the report mass flow rate is listed as their subtraction

(i.e. m.flow and inlet lid: 3.9205kg/s, outlet lid: -4.2329 kg/s(is the ''-'' a sight it's going out of the system?)

and mass flow rate in report: 0.3123 kg/s) I'd wish to know how to avoid that message

and how to correctly set up my boundary conditions.

For my project the more important thing...

When I set up an inlet mass/volume flow rate followed by an atmospheric pressure at the outlet

I again get a different reading of the inlet/outlet surface mass flow rate reading, but this

time without the warning during the calculation. I would like to know the best way to set the

parameters for my pump, I want to know how to set the volume flow rate that the pump provides

and not the flow rate of the fluid at the inlet pipe(or it's the same thing) and how does the

option relative to rotating frame and absolute impact the results.

The parameters I want to use for my analysis are:

Pump flow rate: 100 m^3/h

Angular velocity: 2500RPM

Goals:

1.Inspect the distribution of velocities/pressure/torque

2. Calculate the needed pump power using the torque from each fluid simulated and angular velocity

The main question: How to set up the pump to surely get the correct results? (constant mass flow rate, suction pressure...)

I'd be very thankful if any of you could provide me with the help needed to solve these problems so I can finish my project.

The characteristic dimensions of the pump will be provided in the pdf below:

http://i.imgur.com/X5qpHNh.png

Thanks to everyone who finds time to read this and even more thanks to those willing to help out.

Best regards

Right, so:

First, your model setup. Because you're interested in power requirement at a given flow rate, you need to have mass/volume flow rate as one of your boundary conditions:

Inlet boundary condition should be your mass or volume flow rate.

Outlet boundary condition should be TOTAL pressure, set to 101325Pa (1Bar). This is a combination of static and dynamic pressure, remembering that when you have fluid exiting a fan/pump exhaust, some of the pressure must, by definition, be dynamic.

The vortex crossing the pressure opening warning is just that, a warning. In your case, you would expect air to flow through the exhaust (Pressure opening) so I wouldn't worry about it. I get this warning on Centrifugal fan simulations all the time.

The other problem you have is a little more fundamental; in an incompressible flow the volume flow rate at ALL points in the system will be constant. I suggest you do a little more background reading on fans, and in particular fan curves. This booklet is a personal favourite:

http://www.trox-tlt.de/downloads/075547b0eb5193ae/346_elementary_fan_technology.pdf

Below is a post I wrote to another student who was doing a Pelton Wheel simulation and looking to get the RPM required to provide certain flow conditions. The principle is the same, just liquid rather than gas:

Set up your Pelton wheel model, and use a rotating region to encompass it. You'll need to use a transient study (Time-dependant).Set up a surface goal for torque and then select all of the faces that you want to evaluate the torque on (Then torque times rpm is power consumed).Set your discharge flow and head up as outlet and inlet boundary conditions, and set up surface goals for each of these. Set up your rotating region at a sensible speed (Just your best guess will do fine for now).Then you can do a 'goal optimisation' which falls under the parametric studies menu. Set up rpm as your goal to optimise (Target should be set as 'lowest' or something similar) and Solidworks will work out the lowest rpm at which the Pelton wheel can achieve the flow conditions.Personally I use lots of equation goals (Things like pump developed power (Pressure x flow rate), pump consumed power (Torque x RPM) and then efficiency and so on.) so that I can output the results to excel.Have a play with this and let me know how you get on, I do this with Centrifugal Fans all day long so can help.So there you have how to set up your fan consumed torque readout, you can do fan consumed power (Torque x RPM), fan developed power (Fan eye volume flow * Static pressure) and then calculate efficiency.

What I haven't done is used the Parametric Study feature to vary fluid density, and in my version of Solidworks (2015) it does not seem to be selectable as a parameter to vary. Nevertheless, you can just copy the studies and change the fluid parameters every time, which shouldn't be too ardous.

What might be a much better thing to do is to find the most efficient RPM at which to convey fluids of different densities. In which case, you would need to set up an equation goal for efficiency (Which we mentioned above) and use that for a goal optimisation with RPM as the variable. Then Solidworks varies the RPM until the most efficient point is reached. You can repeat these goal optimisations with each different fluid. (I'm actually doing something pretty similar myself at the moment!).

Have a try and let me know how you get on.

Hope this helps,

Alex