CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Cp > 1 for hemishperical head

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   July 9, 2005, 22:53
Default Cp > 1 for hemishperical head
  #1
Chinmay
Guest
 
Posts: n/a
We are modeling flow over a cylinder with a hemispherical head at various angles to the flow direction. We have a Reynold's number of around 9000 if consider the cylinder diameter as the characteristic length or 90,000 if we consider the cylinder length. We are using unstructured tetrahedral 3D grid. We have created concentric shells around the cylinder to increase the grid density.

We need to measure pressure at 3 points on the cylinder head, which we can validate by comparing the Cp values at these points with the experimental values.

The problem is we have been getting Cp > 1 with Laminar or any k-e model with first order upwind method which is not practically possible.

The problem seems to be in the laminar regime, but we are getting good results by using Reynolds stress model for turbulence which needs a lot of computational time.

Another thing that we are stumped with is if we use velocity inlet instead of pressure inlet then the residuals dropped quickly for velocity inlet as compared to pressure inlet. But Cp was > 1.

The thing is we identified that Cp is > 1 only at very few cells adjacent to the stagnation point. We even tried adapting the grid in regions of high velocity gradient to see if the grid was not sufficiently fine.

1. What is normally the characteristic length in such problems?

2. Is Cp > 1 a gridding problem or turbulence model problem and how do we solve it ?

Thanks in advance.
  Reply With Quote

Old   July 9, 2005, 23:56
Default Re: Cp > 1 for hemishperical head
  #2
zxaar
Guest
 
Posts: n/a
well friend the solution is easier that you assumed, just use prism cells near the cell, with yplus near one, and after that you will see that fluent has cp = at the cylinder had, otherwise you will get cp>1, there is nothing wrong with fluent.
  Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
1.7.x -> buoyantPimpleFoam -> hRhoThermo -> incompressible and icoPoly3ThermoPhysics? will.logie OpenFOAM Programming & Development 1 February 16, 2011 21:52
1.7.x -> buoyantPimpleFoam -> hRhoThermo -> incompressible and icoPoly3ThermoPhysics? will.logie OpenFOAM 0 December 16, 2010 08:08
CAD -> gMsh -> enGrid -> OpenFOAM Problem AlGates OpenFOAM 7 August 6, 2010 12:46
FLUENT shows higher head on the turbine Sanjay Jain FLUENT 0 June 3, 2008 08:41
how to replace piston head in the es-ice software Julian CD-adapco 1 December 20, 2007 01:18


All times are GMT -4. The time now is 12:17.