I'm currently using NX 7.5 with NX flow. I am currently doing a flow simulation for vacuum pump system and would like to know if I can input pressure as an inlet boundary condition. For example, negative pressure to signify vacuum as the inlet and ambient atmospheric pressure for outlet hole.
I would like to find out the velocity or flow rate through the inlet and outlet though this simulation.
You can input pressure as inlet/outlet boundary conditions. You define inlet/outlet conditions using the Flow Boundary Condition simulation object command. The boundary condition types include:
inlet, outlet, opening, internal fan, recirculation loop, convective outflow, static pressure
Inlet and outlet conditions can be defined in terms of:
velocity, mass flow, volume flow, pressure rise, fan curve
You can define a Report simulation object to obtain 3D flow data (velocity, mass flow, etc.) across a region, along with having the standard velocity and mass flux results for the entire model for your review.
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Thanks Mark for your response. However i can see only the following flow boundary condition types on the NX flow software.
Inlet flow, Outlet flow, Opening, Internal Fan, Recirculation Loop
There are no options for convective outflow and static pressure.
Is there any workaround available using the existing flow boundary conditions available to me to input an negative static pressure as boundary condition?
Looks like it is time for an upgrade. Digging through some of the What's New guides for past versions, I see that the Static Pressure type flow boundary condition was added in NX 8.5.
Here's a link to take you to the NX documentation, though now I wonder if you will have access to the versions above 7.5 since the site is webkey controlled.
Here is a snip of the NX 8.5 article.
Static Pressure Flow Boundary Condition
What is it?
Use the new Static Pressure type of Flow Boundary Condition simulation
object to model the fluid with a known static pressure at a location.
The Static Pressure flow boundary condition acts either as an inlet or an
outlet depending on the physics of the model. For example, to model pulsatile flows, such as the blood flow in an artery, you can specify the known static
pressure as a function of time at one end of the artery.
As far as modeling your condition in NX 7.5, that's a question beyond me. Hopefully some flow experts can chime in. I will send this along to some of my colleagues as well.
Good Morniing: There is always some confusion concerning the differences between inlet flow, outlet flow, and opening. Think of inlet and outlet flows as forcing a particular flow rate based on the condition you specify, where as the opening allows the flow rate to "float" based on conditions. Most of the time we have one inlet (or outlet) flow and one or more openings. For your situation you would define one or more openings where you expect the flow to enter, referencing the default ambient condition. You would then define an outlet flow where you are pulling the vacuum. The outlet flow would use mode-pressure rise. The value for the pressure rise would be gage static pressure (relative to the default ambient). Note that you would use a positive value for this since the software already knows it is imposing an outflow condition. I have attached static pressure results where I imposed a .001psi pressure rise outlet flow on the RH end and left the LH end open to ambient. These results are in gage pressure.
Thanks Mark. Hope that I will hear some good news on the workaround from your colleagues.
Thanks Carl_P. I have tried your suggestion but the software was unable to generate a solution in my model. Kindly refer to the pictures attached
Here’s a picture of the model that I’m simulating.
Carl_P, can you explain more on the usage of pressure rise in inlet/outlet flow? I don’t remember this function being taught in the NX flow course.
Thank you all for your assistance
Good afternoon: Your flow solution is diverging. The most common approach to correcting this is to reduce the flow time step. Also take a look at your vacuum pressure boundary condition and make sure it is not unrealsitically low.
Thank you Carl_P. I'm looking into the issue of flow time step and vacuum pressure boundary condition. Will keep the forum posted on the outcome.