initial condition in transient turbine simulation

CFDturbomachinery · October 31, 2014, 16:39

Hi everyone,
I am simulating a water turbine, transient case, in CFX. My simulation is two phase flow: air and water. I got some issues on specifying the initial condition for the turbine. The turbine RPM is already specified (rotating domain) as 500 RPM. At the inlet the volume fraction of water is 1 so for air 0. For the initial condition, i set as follows:
u=0,v=0, w=10 m/s. pressure =1 atm, and for fluid values: water fraction =0, air fraction =1 because initially the domain is filled with air and water is zero. does this make sense? I am concerned with 500 RPM of the turbine initially: that time the turbine is not rotating at all...could anyone help me on this issue?

Thanks much,
Sharon

ghorrocks · November 1, 2014, 05:29

What are you modelling? A Pelton turbine? Please post an image and your output file. Also an image which shows the problem you are having.

CFDturbomachinery · November 3, 2014, 12:55

Thanks Ghorrocks
I am simulating a turbine, shown in figure: Initially the domain is filledup with air and no water,and inlet condition is: water fraction =1, air=0. Outlet is pressure 0 atm relative pressure. To initialize the transient simulation for turbine RPM =200, how do you setup the solver? Because initially the turbine RPM =o and it cant achieve full RPM unless water jets hit the turbine. I want to simulate for t=5 seconds. Thanks.

ghorrocks · November 4, 2014, 07:03

This simulation is MUCH more difficult if you want to do a time-accurate simulation of the first few second of operation.

This simulation is MUCH easier if you model a number of flow rate versus load points and establish the turbine operating curve. You can then work out the turbine speed history as a simple integration of the turbine performance curve.

CFDturbomachinery · November 4, 2014, 16:06

Thanks much. Do you mean specifying the water flow vs turbine speed graph (or a simple equation): to gradually increase the flow rate and turbine speed before it reaches the full flow rate and turbine RPM? how do you do that? how do you write these conditions in CCL and specify the initial condition.

Thanks again

ghorrocks · November 5, 2014, 07:28

I was saying that the simplest approach is to model a series of operating points as steady state simulations. This will then give you an operating curve for the device and you can predict system performance from that.

October 31, 2014, 16:39	initial condition in transient turbine simulation	#1
CFDturbomachinery New Member Sharon Wilcox Join Date: Aug 2014 Location: California, USA Posts: 21 Rep Power: 12	Hi everyone, I am simulating a water turbine, transient case, in CFX. My simulation is two phase flow: air and water. I got some issues on specifying the initial condition for the turbine. The turbine RPM is already specified (rotating domain) as 500 RPM. At the inlet the volume fraction of water is 1 so for air 0. For the initial condition, i set as follows: u=0,v=0, w=10 m/s. pressure =1 atm, and for fluid values: water fraction =0, air fraction =1 because initially the domain is filled with air and water is zero. does this make sense? I am concerned with 500 RPM of the turbine initially: that time the turbine is not rotating at all...could anyone help me on this issue? Thanks much, Sharon

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November 1, 2014, 05:29		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	What are you modelling? A Pelton turbine? Please post an image and your output file. Also an image which shows the problem you are having.

November 4, 2014, 07:03		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	This simulation is MUCH more difficult if you want to do a time-accurate simulation of the first few second of operation. This simulation is MUCH easier if you model a number of flow rate versus load points and establish the turbine operating curve. You can then work out the turbine speed history as a simple integration of the turbine performance curve.

November 4, 2014, 16:06		#5
CFDturbomachinery New Member Sharon Wilcox Join Date: Aug 2014 Location: California, USA Posts: 21 Rep Power: 12	Thanks much. Do you mean specifying the water flow vs turbine speed graph (or a simple equation): to gradually increase the flow rate and turbine speed before it reaches the full flow rate and turbine RPM? how do you do that? how do you write these conditions in CCL and specify the initial condition. Thanks again

November 5, 2014, 07:28		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	I was saying that the simplest approach is to model a series of operating points as steady state simulations. This will then give you an operating curve for the device and you can predict system performance from that.