Transient Flow Over a Turbine Wheel

RichardB86 · October 27, 2010, 07:04

Hi,

I am trying to simulate a flow over a turbine wheel. The wheel accelerates from 0 up to 14500 rpm and the temperature increase from 0 to 1070 degrees. I have been trying to simulate this in ansys CFX, but being fairly new to the program I am not to sure where to start. I have been considering using expressions and step functions, but as I have no prior experience with these. I have had a look through the enclosed tutorials but they don't seem to explain what I am trying to do.

Can anyone help or point me towards a tutorial that might be of use?

Thanks

Rich

michael_owen · October 27, 2010, 09:04

Are you trying to model the transient acceleration of the turbine due to the hydrodynamic torque of the fluid? This is an advanced technique, no matter how you approach it. You can do it using the 6DOF rigid body motion solver that is in beta in CFX R12, but it is beta, so it is pretty much undocumented. You can also do it using fully supported features, but it is very complex, involving mesh motion and some advanced CEL (CFX Expression Language) expressions. There was a very recent thread where a guy provided a CCL (CFX Command Language) snippet illustrating how to do it. Search for a recent thread with the words "angular velocity" and "CCL".

RichardB86 · October 27, 2010, 10:35

Hi Michael

Thanks for your reply. The problem is a conjugate heat transfer problem. I am trying to work out the temperatures of components in a turbine rotor, however I only have inlet and outlet temperatures. I have written an expression that distributes the difference in inlet and outlet temperature between the rest of the components, however this is for a constant temperature. However in reality the component temperature starts from ambient and then heats up to 573 degrees. I am trying to simulate this ramp in temperature so I can look at the heat build up in the components over time.

Thanks

Rich

michael_owen · October 27, 2010, 12:17

Ah; that's much simpler.

Attesz · October 28, 2010, 06:07

Hi,

you have to define a fluid domain for the flow, and solid domains for the components, and interfaces between them. the mesh in solid domains can be coarser, but you have a well resolved boundary layer on the walls to capture the heat transfer properly. You have to define a transient simulation, and if transient rotor-stator interactions are not significant, use adaptive time step to find the best time step value. But, i'm just guessing, if you want to get the heat-up in function of time, propably you have to use constant time step. define a 1d interpolating function for the temperatures, argument unit is time. set an expression, which uses this function, and at inlet boudary condition you can set is. if you use outlet boundary condition, you can set only pressure or massflow etc, so if you have the outlet temperature, you can validate your simulations with that. Of course, you have to put your rotor domain in a rotating frame, and set the rotational velocity as in case of the temperature previously. Do the tutorials in compressor simulation and heat transfer topics, because the main settings of the compressor simulation is the same if you would simulate a turbine.

October 27, 2010, 07:04	Transient Flow Over a Turbine Wheel	#1
RichardB86 New Member Richard Join Date: Oct 2010 Posts: 5 Rep Power: 15	Hi, I am trying to simulate a flow over a turbine wheel. The wheel accelerates from 0 up to 14500 rpm and the temperature increase from 0 to 1070 degrees. I have been trying to simulate this in ansys CFX, but being fairly new to the program I am not to sure where to start. I have been considering using expressions and step functions, but as I have no prior experience with these. I have had a look through the enclosed tutorials but they don't seem to explain what I am trying to do. Can anyone help or point me towards a tutorial that might be of use? Thanks Rich

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October 27, 2010, 09:04		#2
michael_owen Senior Member Michael P. Owen Join Date: Mar 2009 Posts: 196 Rep Power: 17	Are you trying to model the transient acceleration of the turbine due to the hydrodynamic torque of the fluid? This is an advanced technique, no matter how you approach it. You can do it using the 6DOF rigid body motion solver that is in beta in CFX R12, but it is beta, so it is pretty much undocumented. You can also do it using fully supported features, but it is very complex, involving mesh motion and some advanced CEL (CFX Expression Language) expressions. There was a very recent thread where a guy provided a CCL (CFX Command Language) snippet illustrating how to do it. Search for a recent thread with the words "angular velocity" and "CCL".

October 27, 2010, 10:35		#3
RichardB86 New Member Richard Join Date: Oct 2010 Posts: 5 Rep Power: 15	Hi Michael Thanks for your reply. The problem is a conjugate heat transfer problem. I am trying to work out the temperatures of components in a turbine rotor, however I only have inlet and outlet temperatures. I have written an expression that distributes the difference in inlet and outlet temperature between the rest of the components, however this is for a constant temperature. However in reality the component temperature starts from ambient and then heats up to 573 degrees. I am trying to simulate this ramp in temperature so I can look at the heat build up in the components over time. Thanks Rich

October 27, 2010, 12:17		#4
michael_owen Senior Member Michael P. Owen Join Date: Mar 2009 Posts: 196 Rep Power: 17	Ah; that's much simpler.

October 28, 2010, 06:07		#5
Attesz Senior Member Attesz Join Date: Mar 2009 Location: Munich Posts: 368 Rep Power: 17	Hi, you have to define a fluid domain for the flow, and solid domains for the components, and interfaces between them. the mesh in solid domains can be coarser, but you have a well resolved boundary layer on the walls to capture the heat transfer properly. You have to define a transient simulation, and if transient rotor-stator interactions are not significant, use adaptive time step to find the best time step value. But, i'm just guessing, if you want to get the heat-up in function of time, propably you have to use constant time step. define a 1d interpolating function for the temperatures, argument unit is time. set an expression, which uses this function, and at inlet boudary condition you can set is. if you use outlet boundary condition, you can set only pressure or massflow etc, so if you have the outlet temperature, you can validate your simulations with that. Of course, you have to put your rotor domain in a rotating frame, and set the rotational velocity as in case of the temperature previously. Do the tutorials in compressor simulation and heat transfer topics, because the main settings of the compressor simulation is the same if you would simulate a turbine.