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

Water wheel simulation

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   November 11, 2014, 04:17
Default Water wheel simulation
  #1
Senior Member
 
Join Date: Oct 2014
Posts: 124
Rep Power: 7
Ema40 is on a distinguished road
Hi everybody.

I am simulating a model of water wheel (a breastshot water wheel). The water enters the buckets and pushing on the blades make the wheel rotate. The simulation converges and I have been able to simulate the multiphase fluid (air+water, since the wheel is in a open channel) and the rotating domain. The water level inside the buckets is more or less the same as that estimated theoretically (so it is ok), the exiting flow rate is the same as the entering one (so the mass conservation is ok), etc. Despite this, the torque and the moment coefficient are very lower than that estimated theoretically and measured by experiment. I have used different turbulence models (k-eps standard, k-eps RNG, k-eps Realizable, k-omega, k-omega SST laminar, Reynold stress ), different options (low reynolds correction, curvature correction, etc.), different numerical schemes and different mesh sizing, but I have obtained always the same results.

Can anyone of the members help me with some advices?
Thank you
Ema40 is offline   Reply With Quote

Old   November 11, 2014, 11:49
Default
  #2
Senior Member
 
Andrew Kokemoor
Join Date: Aug 2013
Posts: 122
Rep Power: 9
Kokemoor is on a distinguished road
If you compare the total (kinetic + potential) energy of the water at the inlet to the outlet, does that correspond at all to either your CFD results or theoretical ones?

(mass flow rate)*(gravity)*(height change) + 1/2*(mass flow rate)*((average velocity in)^2-(average velocity out)^2) = (torque)*(wheel rotation rate) + (energy losses)

This is a good sort of way to check that torque is being measured correctly.
Kokemoor is offline   Reply With Quote

Old   November 12, 2014, 05:22
Default
  #3
Senior Member
 
Join Date: Oct 2014
Posts: 124
Rep Power: 7
Ema40 is on a distinguished road
Thank you. The problem is that I calculate the difference of energy, but this difference is due both to the losses both to the torque and I don't know in what proportion. I compare the numerical torque to that measured experimentally and it is wrong. I can't understand why.

Thank you
Ema40 is offline   Reply With Quote

Old   November 12, 2014, 14:25
Default
  #4
Senior Member
 
Andrew Kokemoor
Join Date: Aug 2013
Posts: 122
Rep Power: 9
Kokemoor is on a distinguished road
Quote:
Originally Posted by Ema40 View Post
The problem is that I calculate the difference of energy, but this difference is due both to the losses both to the torque and I don't know in what proportion.
In the theoretical case, you should know the proportion. Can you compare your inlet and exit flow velocities to the theory?
Kokemoor is offline   Reply With Quote

Old   November 13, 2014, 03:35
Default
  #5
Senior Member
 
Join Date: Oct 2014
Posts: 124
Rep Power: 7
Ema40 is on a distinguished road
Thank you.
Yes.
The problem is that the numerical torque is very different to the experimental and theoretical torque, despite the other quantities are right (water levels, velocity, etc.)

I have discovered few hours ago that the static pressure inside the wheel, in zones where only air is present, is -5000 Pa and I think it is totally wrong!! The wheel is in an open environment and the air is lightweigh...
Ema40 is offline   Reply With Quote

Reply

Tags
multiphase, rotating domain, turbine, water wheel

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Vertical axis water turbine simulation SHIKHA BHUYAN CFX 1 September 15, 2014 08:40
Simulation of Water Turbine with CFX hydroturbines CFX 0 July 23, 2014 16:58
Solid object falling in water tank simulation cassini83 CFX 0 June 11, 2014 20:00
Simulation of tiltable bucket with water jurij CFX 2 August 21, 2012 21:49
Mass conservation problem in mixing tank multiphase simulation rockewan FLUENT 0 April 6, 2010 13:34


All times are GMT -4. The time now is 23:00.