Superimposing a developed Velocity Profile at a different plane

hasanifte · March 30, 2015, 16:00

Hi,

I want to superimpose a developed velocity profile at the inlet of a small model. The velocity profile is at a distance 227 mm from the inlet. I want to extract that velocity profile and give it at the inlet of a small model

How this is possible?

Please share easy method.

Regards,

Hassan

`e` · March 30, 2015, 16:04

What is the geometry of your inlet? How are you currently imposing the velocity inlet condition? If it's pipe flow, then you could use the analytic solution.

hasanifte · March 30, 2015, 16:18

Thanks for your reply.

Geometry = rectangular duct

I am using average velocity of 0.5 m/s at the inlet.

`e` · March 30, 2015, 16:49

Are you modelling 2D or 3D?

A long winded approach:

extract the developed profile using CFD-Post (either a line for 2D or a surface for 3D)
manipulate the x (and y) coordinates by scaling them to your smaller geometry
use this data file as your velocity inlet condition (may require changing format for Fluent to read)

Computational approach: increase the geometry to allow the flow to become fully developed.

Quick approach: read the section on "Reading and Writing Profile Files" in Fluent's user guide.

hasanifte · March 30, 2015, 17:12

Quote:

Originally Posted by `e`

Are you modelling 2D or 3D?

A long winded approach:

extract the developed profile using CFD-Post (either a line for 2D or a surface for 3D)
manipulate the x (and y) coordinates by scaling them to your smaller geometry
use this data file as your velocity inlet condition (may require changing format for Fluent to read)

Computational approach: increase the geometry to allow the flow to become fully developed.

Quick approach: read the section on "Reading and Writing Profile Files" in Fluent's user guide.

My model is 3d. Model remain same just the length is reduced.ie distance from the inlet is 227 mm. Height and width remain same.

How to extact points from the surface.

Can you explain point 3. Which format? and how to apply the velocities in fluent.

Thanks once again.

`e` · March 30, 2015, 18:22

If your model doesn't change in width or height (dimensions which would alter the inlet boundary dimensions) then this task is trivial. Does your 3D model of the duct include any other features blocking/affecting the flow, or is the outlet simply a developed profile? If your geometry is a simple duct, then use my "quick approach" above.

hasanifte · March 30, 2015, 18:35

There is a step (obstruction) in between the channel... it is a developed velocity profile.

But I dont know how to extract points from a surface.

`e` · March 30, 2015, 19:09

It appears you're trying to model flow over a step. Why are you trying to reduce the entrance length in the first place? The computational requirements are negligible for including an entrance length as your mesh is coarse in this region.

I assume (from your mesh) that you're new to CFD and suggest you have a read of this tutorial on modelling a sudden expansion in laminar pipe flow.

hasanifte · March 30, 2015, 19:47

My flow is turbulent. The idea behind generating a coarse mesh is to save computational time. I have generated a fine mesh at step to capture the reattachment length...

I still want to go more fine at other regions (away from step-near outlet) as I want to extract data at various locations downstream. First I am trying to capture reattachment length.

I have reduced entrance length to save computational power. My entrance length was 1200 mm. It takes around 25-30 D to develop mean velocity profiles. where D is hydraulic diameter of duct. I have reduced it to 240 mm

March 30, 2015, 16:00	Superimposing a developed Velocity Profile at a different plane	#1
hasanifte Member Hassan Iftekhar Join Date: Jan 2015 Posts: 40 Rep Power: 11	Hi, I want to superimpose a developed velocity profile at the inlet of a small model. The velocity profile is at a distance 227 mm from the inlet. I want to extract that velocity profile and give it at the inlet of a small model How this is possible? Please share easy method. Regards, Hassan

March 30, 2015, 16:49		#4
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	Are you modelling 2D or 3D? A long winded approach: extract the developed profile using CFD-Post (either a line for 2D or a surface for 3D) manipulate the x (and y) coordinates by scaling them to your smaller geometry use this data file as your velocity inlet condition (may require changing format for Fluent to read) Computational approach: increase the geometry to allow the flow to become fully developed. Quick approach: read the section on "Reading and Writing Profile Files" in Fluent's user guide. hasanifte likes this.

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March 30, 2015, 16:04		#2
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	What is the geometry of your inlet? How are you currently imposing the velocity inlet condition? If it's pipe flow, then you could use the analytic solution.

March 30, 2015, 16:18		#3
hasanifte Member Hassan Iftekhar Join Date: Jan 2015 Posts: 40 Rep Power: 11	Thanks for your reply. Geometry = rectangular duct I am using average velocity of 0.5 m/s at the inlet.

March 30, 2015, 18:22		#6
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	If your model doesn't change in width or height (dimensions which would alter the inlet boundary dimensions) then this task is trivial. Does your 3D model of the duct include any other features blocking/affecting the flow, or is the outlet simply a developed profile? If your geometry is a simple duct, then use my "quick approach" above.

March 30, 2015, 19:09		#8
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	It appears you're trying to model flow over a step. Why are you trying to reduce the entrance length in the first place? The computational requirements are negligible for including an entrance length as your mesh is coarse in this region. I assume (from your mesh) that you're new to CFD and suggest you have a read of this tutorial on modelling a sudden expansion in laminar pipe flow.

March 30, 2015, 19:47		#9
hasanifte Member Hassan Iftekhar Join Date: Jan 2015 Posts: 40 Rep Power: 11	My flow is turbulent. The idea behind generating a coarse mesh is to save computational time. I have generated a fine mesh at step to capture the reattachment length... I still want to go more fine at other regions (away from step-near outlet) as I want to extract data at various locations downstream. First I am trying to capture reattachment length. I have reduced entrance length to save computational power. My entrance length was 1200 mm. It takes around 25-30 D to develop mean velocity profiles. where D is hydraulic diameter of duct. I have reduced it to 240 mm