[basilwatson]

Hi all
Sorry for the highly "scientific " terminology" I couldnt think of a better way to describe it

I have modeled oil flow in an engine no problems so far, using Freecad addon CFD

However, I would like to "model" a jet stream of oil so that i can estimate its distance and angle just roughly

so I can get a handle of sizes before I start cutting.

how would I go about this?

model the bearing that produces the oil jet then put that inside a mesh?

and what sort of solver should I use

Hope this makes sense

Kind regards

Stephen

[Tobermory]

This is not a trivial problem to solve.

If you think about the physics, the oil will exit the nozzle as a liquid stream ... fine so far. But what happens next? Does it remain a coherent stream (think of a garden hose set to a really low flow rate), or does it atomise (break up into a droplet spray?

This depends on the Capillarity number and Ohnsorge numbers ... which depend on the fluid mechanical properties. My guess is that it will probably break up, so you'll then need to model a spray of droplets, with an appropriate size distribution. You can probably ignore evaporation, since you're calling it oil, i.e. I assume that it's way below its flash point. Regardless, simulating the above is not a simple look-see calculation.

[basilwatson]

Originally Posted by Tobermory

This is not a trivial problem to solve.

If you think about the physics, the oil will exit the nozzle as a liquid stream ... fine so far. But what happens next? Does it remain a coherent stream (think of a garden hose set to a really low flow rate), or does it atomise (break up into a droplet spray?

This depends on the Capillarity number and Ohnsorge numbers ... which depend on the fluid mechanical properties. My guess is that it will probably break up, so you'll then need to model a spray of droplets, with an appropriate size distribution. You can probably ignore evaporation, since you're calling it oil, i.e. I assume that it's way below its flash point. Regardless, simulating the above is not a simple look-see calculation.

We could make a few assumptions based on observation Sae20 laminar 100 degc 50mm/sec exit speed ye garden hose at low flow rate

I can be difficult ,, But i dont think it needs to be

Stephen

[Tobermory]

Aaah - well, if it's a laminar, coherent stream (i.e. low velocity release), then you can calculate the trajectory from simple ballistics to reasonable accuracy, since the oil stream will not decelerate much from air resistance.

Time to break out your school maths: say it issues horizontally at velocity U1, from a breach a height h above ground, then the time taken to drop to ground level is:



solve for t. In this time, the oil travels a distance



That should be enough for you?

[basilwatson]

Originally Posted by Tobermory

Aaah - well, if it's a laminar, coherent stream (i.e. low velocity release), then you can calculate the trajectory from simple ballistics to reasonable accuracy, since the oil stream will not decelerate much from air resistance.

Time to break out your school maths: say it issues horizontally at velocity U1, from a breach a height h above ground, then the time taken to drop to ground level is:



solve for t. In this time, the oil travels a distance



That should be enough for you?

Hahaha Thank you !

You know, I always worry about posting questions on the internet, I know what Im thinking but often the head doesnt communicate with fingers But , you often get that " ahhh that will work" from a comment or picture

I hadnt thought of ,,, a simple ballistics solve for t That will do fine

But just out of curiosity , Is there a " open FOAM " solver or CFD approach that looks at a "free steam " exiting a tube ?

Thanks for you for your help

Im curious now to see if the calcs line up with actual!

Stephen

[Tobermory]

No problem - happy to help!

Originally Posted by basilwatson

But just out of curiosity , Is there a " open FOAM " solver or CFD approach that looks at a "free steam " exiting a tube ?

Yes - you could use interFoam, ie a VOF solver (check out the "damBreak" tutorial) with laminar flow. The only tricky bit is making sure that you have the a fine enough mesh resolution in the path of the liquid, so if you were being ultra fancy you would either run the simulation with adaptive nesh refinement, or you wouyld run the simulation several times, each time refinining the mesh based on where the liquid went.

[basilwatson]

Originally Posted by Tobermory

No problem - happy to help!
Yes - you could use interFoam, ie a VOF solver (check out the "damBreak" tutorial) with laminar flow. The only tricky bit is making sure that you have the a fine enough mesh resolution in the path of the liquid, so if you were being ultra fancy you would either run the simulation with adaptive nesh refinement, or you wouyld run the simulation several times, each time refinining the mesh based on where the liquid went.

Thank you for your ts just help

really valuable

Ive finished the job and the bike is up and running so now i its just me "playing" ( learning ) when I get the time

I must admit I am "warming to " openFoam as iI understand it more

Thank you

Stephen